The Genetical Society of Great Britain

Heredity (1981), 46 (2), 285-294

1981.The Genetical Society of Great Britain

THEGENETICAL SOCIETY ABSTRACTS of papers presented at the HUNDRED AND NINETY- THIRD MEETING of the Society held on 14th and 15th November, 1980, at UNIVERSITY COLLEGE LONDON.

SOME OBSERVATIONS ON LATERAL ASYMMETRY OF CENTROMERIC HETEROCHROMATIN IN HUMAN CHROMOSOMES 1, 3 and 4 VASANTHA BRITO—BABAPULLE Department of Cancer Research, Mount Vernon Hospital, Northwood, Middlesex, HA6 2RN. Lateral asymmetry can be demonstrated in certain C—band regions when chromosomes which have undergone one replication cycle in BrdU are stained with 2 per cent Giemsa made up in a 03 M Na2HPO4 solution at a pH of 104. This technique has an advantage over other methods for showing the presence of lateral asymmetry in that chromosomes in first division are G—banded, and polymorphism for lateral asymmetry in the C-band regions of chromosomes 3 and 4, which has not been described previously, can be demonstrated. Lateral asymmetry is thought to result from an unequal interstrand thymine distribution in regions of highly repetitive DNA, such as satellite DNA, which would lead to a differential incorporation of BrdU into the 2 chromatids. So far there is no evidence for the presence of satellite DNA on chromosome 4, which suggests the presence of nonsatellite repetitive sequences, sufficiently repetitive to give rise to an interstrand thymine difference. Using Giemsa-li banding and the above technique, evidence is also provided for the theory that compound asymmetry in the C-band region of chromosome 1 is due to the presence of 2 segments containing 2 distinct species of DNA differing in base composition with different thymine rich strands.

METHIONINESULPHOXIMINE RESISTANT MUTANTS OF CHO CELLS A. H. WILSON Genetics Department, University of Glasgow, Glasgow, Gil 5JS. Methioninesulphoximine (Msx) is a highly potent irreversible inhibitor of glutamine synthetase (GS), an enzyme whose levels are regulated both within and between cell types. Starting with the CHO-Ki proline aprt cell fine, a complementing line, G102 prolineaprt, was selected. In each line variants resistant to methionine sulphoximine were selected by multistep selection. These were about 40 x more resistant than their parents. The resistant cell lines had elevated GS levels, about 10 Xtheparental levels, irrespective of whether the enzyme was glutamine repressed or not. The GS of the resistant cells was as sensitive to Msx as the wild-type enzyme both in vivo and in vitro. The variant cells show no obvious chromosome abnormalities that could relate to the GS overproduction. Hybrids between the resistant cells and complementary wild-type cells show a semi-dominant mode of expression of the Msx resistance. It is not yet known whether the GS overproduction is caused by GS gene amplification or by mutation affecting a control element. 285 286 ABSTRACTS

THEINDUCTION OF RIBOSOMAL DNA CHANGES IN FLAX C. A. CULLIS John Innes Institute, Colney Lane, Norwich, NR4 7UH. Heritablechanges can be induced in some flax varieties when they are grown for one generation in certain envilonments (Durrant, A., Heredity, 17,27,1962). Two characters susceptible to change are the rDNA amount and the isozyme band pattern of peroxidase. The rDNA amount and peroxidase isozyme band pattern were determined during growth of susceptible plants under inducing conditions. Under one Set of conditions this amount decreased. The change occurred during a short period of growth under inducing conditions. The plants in which decreased rDNA amount had been induced transmitted this reduced level to their progeny. No change in the peroxidase isozyme band pattern was observed during growth under inducing conditions although the progeny of plants grown under one set of conditions did show alteration in this pattern.

SPONTANEOUSMALE RECOMBINATION ASSOCIATED WITH HYBRID DYSGENESIS IN DROSOPHILA MELANOGASTER M. J. KEARSEY and P. EGGLESTON University of Birmingham, P.O. Box 363, Birmingham, B15 2TT. Crossesbetween laboratory stocks and extractions from wild populations have recently been shown to produce non-reciprocal genetic aberrations commonly termed hybrid dysgenesis, which appear to arise from a nuclear cytoplasmic interaction. Dysgenic traits incl.ide male recombination, increased mutation rates, high frequencies of meiotic abnormalities and varying degrees of male and female sterility and, as far as they have been studied, the genetic and cytoplasmic control of these traits are essentially similar. Two long inbred lines extracted from the TEXAS population have been shown to possess factors on the third chromosome capable of inducing similar male recombination frequencies. The two lines, however, display marked differences in the distribution of recombination events particularly in the left arm of chromosome III. The results suggest that a proportion (perhaps the majority) of these events are premeiotic in origin.

MODIFICATIONOF MR MUTATOR ACTIVITY IN REPAIR-DEFICIENT STRAINS OF DROSOPHILA MELANOGASTER J. C. J. EEKEN and F. H. SOBELS Department of Pediation Genetics and Chemical Muta genesis, University of Leiden, The Netherlands. MRis expressed as mitotic recombination in males, sterility, and mutator activity in the progeny of MR males crossed to females from any strain of Drosophila melanogaster. There is a marked locus-specificity for the induction of visible mutations and chromosome breaks by MR. Visible mutations, induced by MR are unstable. One explanation of the mutator activity of MR is that MR causes breaks at specific sites, where subsequently insertion sequences become integrated. To examine whether excision and incorporation of insertion sequences by MR is possibly associated with enzymatic pathways involved in DNA repair, the following experiments were carried out. MR was introduced into males deficient for excision (mei9a) or post-replication repair (mei45) or into males carrying both repair-deficient mutations. MR activity was recorded by the induction of visible mutations at the sn (singed) and ras (raspberry) loci. The spontaneous mutation frequency for sn is 02 iO5 (1/490,000) and for raspberry, 04 10 (2/490,000) (Schalet, Proc. Xth mt. Cong. Genet. (Montreal) Vol. 2, 252, 1958). When MR is introduced into repair-proficient males the frequency of sn mutations is 185 .10(43/23,299) and of ms 34 .10(8/23,299) (Green, PNAS 74, 3490, 1977). In males deficient for both excision and post-replication repair (meisa,mei4bos) MR mutator activity is significantl enhanced; in two independent experiments the frequency of sn amounts to 304 10 ABSTRACTS 287

(93/30,542) and 239 i0 (73/30,554) and of ras to 17010 (52/30,542)and 134 10 (41/30,554). By contrast neither mei9 or mei41°5 alone result in a change of the mutation frequencies; with nleisa,12310 (50/40,583) sn and 54 i0 (21/40,583) ras mutations were recorded, and in combination with mei4WS 111 i0 (30/27,127) and 52 10 (14/27,127) ras mutations were observed. It would thus appear that only in the presence of both repair-deficient mutants, is the mutation activity of MR modified. In order to see whether, perhaps, the combination of mei9 and mei4105 could be held responsible for observed enhancement, sn and ras mutation frequencies were determined in double mutant males without MR; no an and 2 ras mutations were found among 119,671 tested chromosomes.

ROLEOF THE CYTOPLASMIC RIBOSOME IN CYCLOHEXIMIDE RESISTANCE IN COPRINUS CINEREUS J. D. TRAYNOR and JANE NORTH Department of Biological Sciences, City of London Polytechnic. UVmutagenesis of cycloheximide sensitive strains of the basidiomycete fungus, Coprinus cinereus,has resulted in the production of over one hundred resistant mutants. In vivo growth in a cycloheximide sensitive strain is inhibited by 10 ig/ml cycloheximide but some of the resistant strains are able to grow at forty-fold higher concentrations. The location and number of genes determining cycloheximide resistance has been partly determined (North, J., Heredity, 40,331,1978), these can be recessive or dominant in the presence of a modifier gene. Of particular interest are those mutants for which expression of cycloheximide is brought about by a modification of the cytoplasmic ribosome. A cell-free protein synthesising system has been developed and resistant ribosomes have been found in two of the highly resistant mutants. Resistant ribosomes can be used as a means of studying genetic interaction: when one compares cycloheximide resistance in the three stable nuclear states that exist for Coprinus cinereus, namely, haploid, diploid and dikaryon, it is possible to gain an insight into ribosome assembly and function.

IDENTIFICATIONOF STRUCTURAL GENES IN THE pm GENE CLUSTER OF ASPERGILLUS NIDULANS S. A. JONES, H. N. ARST, Jr., and D. W. MACDONALD Department of Genetics, University of Cambridge. Theconversion of exogenous L-proline to endogenous L-glutamate in the fungus Asper- gillus nidulans involves a highly specific L-proline permease and the enzymes proline oxidase and &-pyrroline-5-carboxylate (P5C) dehydrogenase (Arst and MacDonald, Nature, 254, 26, 1975), The genes affecting proline catabolism are clustered in the order: prnA—prnD— control region—prnB—prnC (Arst and MacDonald, Molec. gen. Genet., .163, 17, 1978). Cis-acting regulatory mutation affecting the expression of at least prnB map in the control region (Arst, MacDonald and Jones, J. gen. Microbiol., 116, 285, 1980), and deletion of the control region considerably reduces expression of at least prnC (Arst and MacDonald, Molec. gen. Genet., 763, 17, 1978). Using a combination of immunological analysis and studies with conditional mutants, we have established that prnD and prnC are the structural genes for proline oxidase and P5C dehydrogenase, respectively. prnB is very likely to be the structural gene for the praline permease. In contrast, our data virtually rule out any structural role for the prnA product in these activities. prnA is probably a positive acting regulatory gene mediating proline induction of the syntheses of the products of the other pm genes. 288 ABSTRACTS

THEROLES OF NADPH, NADP-GLUTAMIC DEHYDROGENASE AND AMMONIA IN THE REGULATION OF NITROGEN METABOLISM IN A SIMPLE EUCARYOTE J. A. PATEMAN Genetics Department, Research School of Biological Sciences, Australian National University, Canberra, 2601. Awide range of enzyme activities and metabolite uptake systems in the simple eucaryotes Aspergillus, Neurospora and Saccharomyces, are affected by growth with ammonia as the nitrogen source. These systems, which are best documented in A. nidulans, include: nitrate and nitrite reductase, purine uptake systems, purine oxidation enzymes, urease, urea uptake and glutamate uptake. In general these systems determine the utilization of metabolites which are nitrogen but not carbon sources. It exogenous ammonia is available the activity of all these systems is low, i.e., ammonia repression. In the absence of ammonia, the activity of the systems is high, i.e., ammonia derepression. It is usually assumed that ammonia is the co-effector for the control of these systems. The concentrations of NADPH and NADH and the activities of the NADP and NAD glutamate dehydrogenase have been measured in the wild type and the gdhA ,tatnAand areAD mutants in a variety of growth conditions affecting nitrogen regulation. The results indicate that NADPH and not ammonia is the probable co-effector in nitrogen regulation. A hypothesis concerning the interactions of NADPH, NADP glutamic dehydrogenase and ammonia to regulate nitrogen metabolism in simple eucaryotes will be presented.

IPTGEFFECTS ON SPONTANEOUS, CAFFEINE-AND ULTRAVIOLET-INDUCED LAC REVERSIONS IN ESCHERICHIA COLI Ki 2 COLIN H. CLARKE and ZEENA H. AL-HASANI School of Biological Sciences, University of East Anglia, Norwich, NR4 7TJ. Thefrequency of spontaneous Lac reversions of the polar lac Ztrameshiftmutant ND16O (Clarke and Wade, Mutation Res., 28, 123, 1975) is strongly reduced in the presence of a 05 mM concentration of the gratuitous inducer of the lactose option, isopropy/-/3-D-thio- galactoside (IPTG). This antimutagenic effect of IPTG is found for lac cells growing in liquid complete medium, liquid minimal glycerol medium, or undergoing limited growth on plates of minimal-high lactose-low glycerol agar. A similar influence of IPTG virtually abolishes the mutagenic induction of Lac reversions of ND16O by replication in the presence of caffeine, 1 mgm/mI (Clarke and Shankel, Mutation Res., 46, 243, 1977). In ultraviolet-induced Lac reversion experiments cells were grown before irradiation in nutrient broth and plated, after irradiation, on minimal lactose agar with limited (25 per cent by volume) nutrient broth enrichment. Under these conditions, and with comparisons made at equal UV doses, pre-irradiation growth of ND 160 with IPTG leads to little alteration in UV-induced reversion frequencies. In marked contrast, post-irradiation plating in the presence of IPTG abolishes the UV reversion response of NDI6O. However, with the lac Zmissensemutant U141 growth in the presence of IPTG before UV irradiation increasestheinduced reversion response, but there is no effect of post-irradiation addition of IPTG to the plating medium. Finally, with lac Zambermutant U281 under nutrient broth growth conditions IPTG causes an approximate halving of the spontaneous reversion frequency. UV-induced reversions of U281 are reduced in frequency by IPTG present either before or after UV irradiation. Thus IPTG may exert antimutagenic or mutagen-enhancement effects depending upon the particular conditions and lac Z allele used. ABSTRACTS 289

THEMUTAGENIC ACTIVITY OF SACCHARIN IN SCHIZOSA CCHAROMYCES POMBE MOHAMMED A. K. IBRAHIM, HAMED AL-ZAIDY, arid MOHAMMED S. JABRA Department of Biology, College of Science, University of Sulaimaniyah, Sulaimarriyah, Iraq. Themutagenic activity of various concentrations (16, 32 and 64 mg/mi) of Saccharin have been tested for its ability to induce cycioheximide resistant mutants of the yeast Schizosac- cha rain yces pombe. The mutation frequency was calculated at 0, 30, 60 and 120 minutes of treatment with Saccharin, after allowing phenotypic expression for four and twenty hours. The results indicate that Saccharin at 32 and 64 mg/mi has a weak Inutagenic effect upon cells of S. pombe collected at mid exponential phase, whereas 16mg/mi showed no mutagenic effect. The concentration of Saccharin used showed no mutagenic effect upon cells of S. pombe during the stationary phase of growth.

THEIDENTIFICATION AND PROPERTIES OF CONVERSION CONTROL FACTORS 2, 3 AND 4 AFFECTING A SINGLE LOCUS IN THE PASADENA STRAINS OF ASCOBOLUS IMMERSUS S. HELMI and B. C. LAMB Botany Department, Imperial College, London SW7 2BB. Geneconversion parameters at white ascospore locus I are controlled by three separate conversion control factors (ccfs), the different genotypes of which give different locus I conversion frequencies averaging from 066 per cent to about 23 per cent. Where appropriate, ccl "alleles" are designated according to their effect on conversion frequencies: E, dominant enhancer; e, recessive reducer; R, dominant reducer; r, recessive enhancer. The three forms of ccf-2, ccf-2(P), ccf-2(K) and ccf-2(91), previously called the P, K and 91 factors (Lamb and Helmi, Genet. Res. 32: 67-78, 1978), are very closely linked to locus I but do not co-convert with it; the three forms show incomplete dominance to each other, with cis/trans position effects on conversion of locus I. The "Super" factor (Helmi and Lamb, Heredity, 42,273, 1979) has now been shown to have two unlinked, interacting components, ccf-3 and ccf-4, and approximately doubles whatever gene conversion frequency at locus I is determined by ccf-2 factors. ccf-3 is unlinked to locus 1, while ccf-4 is loosely linked to locus I. Of the two conversion-enhancing alleles of the "Super" combination, ccf-3E is dominant but ccf-4r is recessive, with ccf-4r dominantly epistatic to ccf-3 and ccf-3e recessively epistatic to ccf-4. From these data from pedigree studies and large numbers of different crosses, we deduce that ccf-3E codes for a diffusible product which reaches the unlinked locus I where it increases hybrid DNA initiation frequency, probably through interaction with the ccf-2 controls adjacent to or within locus I. ccf-4R could be an alternative binding point for ccf- 3E product or could code for a diffusible product combining with that from ccf-3E, so deterring it from enhancing conversion at locus I.

CHROMOSOMALREQUIREMENTS FOR MALE FERTILITY D. LINDSLEY Department of Biology, University of California, Sen Diego, U.S.A. Weestimate that the normal functions of as many as 2000 genes are necessary but not sufficient for normal spermatogenesis; there are additional constraints on sex-chromosome configuration. For example, approximately 80 per cent of all translocations between the X- chromosome and either chromosome 2 or 3 are male sterile. Translocations that interchange, in the aggregate, less than half a chromosome arm are generally fertile as are a fraction of those with breakpoints in the proximal X-heterochromatin; the remainder are male sterile. We postulate that X-autosome translocations remove X-chrornosome genes from, and place 290 ABSTRACTS autosomal genes under, control of a cis-acting proximally located X-chromosome element normally responsible for inactivating X-linked genes in advance of autosomal genes in the primary spermatocytes. In agreement with this supposition is the observation that male-fertile T(X;A)'swithbreakpoints in the centric heterochromatin are broken more proximally than the male-sterile T(X;A)'s, which are presumably broken within or distal to the hypothetical control element. Attempts to induce male sterility by deletion of this element suggest that sequences dispersed within the X-heterochromatin compete with unlinked homologous sequences for a substance or substances necessary for cis-inactivation of the X- chromosome in the primary spermatocyte.

THECONTROL OF VITELLOGENESIS IN DROSOPHILA MELANOGASTER MARY BOWNES Department of Molecular Biology, University of Edinburgh. Thereare three yolk polypeptides synthesised in the fat bodies and ovaries of mature females of D. melanogaster. All three map on the X-chromosome. Less of each polypeptide is produced in hemizygous females; thus if dosage compensation exists it is incomplete. Ecdys- terone controls fat body synthesis, but we do not yet know what controls ovarian synthesis. Juvenile hormone regulates the uptake of yolk into the oocyte. Mutations such as transformer and doublesex which alter the morphological sexual phenotype of adults also determine whether the yolk protein genes are active or inactive. Thus the yolk proteins of Drosophila provide us with a model system for studying the mechanism of control of developmentally regulated genes.

ANEW CELL MARKER FOR CLONAL ANALYSIS IN DROSOPHILA P. A. LAWRENCE MAC Laboratory of Molecular Biology, University Postgraduate Medical School, Cambridge. Wehave isolated several alleles of a gene affecting the mitochondrial enzyme succinic dehydrogenase. Most alleles are homozygous lethal but one is temperature sensitive for viability. All alleles are homozygous viable in cells of large clones, and, after staining for succinic dehydrogenase, have a clear phenotype in all of the tissues so far tested. Some preliminary results with this cell marker will be described. We intend to use it to search for compartments in the internal organs.

NEUROGENETICSOF COURTSHIP IN DROSOPHILA JEFFREY C. HALL Brandeis University, Waltham, Mass. USA. Courtshipin Drosophilahasbeen analyzed using genetic variants that disrupt this behaviour. Some of the mutations define genes that appear to be directly involved in the programming of the fixed action patterns of reproduction. These are courtship-specific mutants such as fruitless,celibate, coitus-in terruptus, andstuck.Othervariants we have used are not courtship-specific, but these mutants with visual or olfactory defects also have their courtship impaired in specific ways, and are valuable in assessing the roles of these sensory modalities in both male and female sex behaviour. The key mutants in these experiments have been in the no-receptor-potential(blind),optomotor-blind,andsmell-blind (olfactory-defective) genes. The fruitless mutant also has important Connections to the olfactory control of Courtship. An additional class of mutations has been used to disrupt the nervous system, and show connections between courtship and higher functions that are controlled by these central tissues. These mutants have defects in complex behaviour such as learning, memory, and circadian rhythmicity, and the discovery of their specific abnormalities of courtship has revealed unexpected interrelationships among these centrally controlled functions. One of the courtship activities we have probed in particular detail has been the courtship song, which has short-term ABSTRACTS 291 fluctuations that are disrupted by periodmutations(originally discovered on the basis of abnormal diurnal rhythms). The control of courtship song, and the oscillations in it, by the CNS has also been probed through the use of acetylcholinesterase mutants, in conjunction with genetic mosaics that have aberrant neurotransmitter metabolism in defined portions of the nervous system.

THEGENETICS OF ALCOHOL DEHYDROGENASE OF DROSOPHILA MELANOGASTER M. ASHBURNER Department of Genetics, University of Cambridge, Cambridge. Remarkablyfew genes of Drosophila are sufficiently well characterised for detailed studies of their control. One is that coding for alcohol dehydrogenase (Adh). This gene codes for a polypeptide of 254 amino acids (Thatcher, 1980, Biochem. J., 187, 785). Mutations lowering ADH activity can be selected using, for example, pentenol and, conversely, mutations increasing activity can, at least in principle, be selected on the basis of tolerance to ethanol. I will review recent studies of the genetic organisation of Adh and discuss the results of attempts to identify 'control" mutations affecting this gene. The genetic environs of Adh have been "saturated" for mutations and the loci contiguous to this gene provisionally identified. The ways in which these contiguous loci can be used to aid the analysis of the control of Adh will be illustrated. The gene has been cloned (Goldberg 1980, Proc. nat. Acad. Sci., in press) and the clones are now being used to analyse the nature of spontaneous and induced mutations affecting Adh.

THEPOPULATION GENETICS OF ALCOHOL DEHYDROGENASE B. C. CLARKE Genetics Research Unit, University Hospital, Nottingham. Thealcohol dehydrogenase locus in D. melanogaster has attracted interest because it is an excellent system for working out the circuits of genetic control. The result is that we know more about the fine genetics and molecular biology of Adh than about any other locus in Drosophila, perhaps excepting rosy. Adh is polymorphic for electrophoretic variants in most natural populations of melanogaster, and the volume of information about the locus makes forming and testing evolutionary hypotheses easier and more rigorous than is usually possible.

AMOLECULAR ANALYSIS OF THE GENES FOR LARVAL SERUM PROTEINS D. B. ROBERTS Genetic Laboratory, Department of Biochemistry, University of Oxford. Wehave cloned the genes for the three subunits of larval serum Protein-i. The recom- binant DNAs hybridise in situ to polytene chromosome positions ilA8, 21D4 and 6iAl consistent with the known cytogenetic positions of the a, i3 and y genes, respectively. Heteroduplex analysis has allowed us to predict the evolutionary relationship between the three genes. Each gene contains an intervening sequence near its 5' terminus. We plan to use a combined molecular and genetic analysis to study the coordinate expression of these genes. 292 ABSTRACTS

ARAPID PROCESS OF ADDITION AND ELIMINATION OF REPETITIVE AND RIBOSOMAL GENE SEQUENCES IN THE MELANOGASTER SPECIES SUBGROUP TOM STRACHAN, ENRICO COEN and GABRIEL DOVER Department of Genetics, Downing Street, Cambridge, CB2 3EH. Tounderstand mechanisms of genome evolution, the sequence arrangement and chromosome distribution of repetitive and ribosomal gene families have been investigated within and between seven sibling species. These studies reveal rapid and paradoxical features of sequence alteration not explicable in tetms of random base substitution alone. The species' genomes contain over 15 abundant repetitive DNAs with a wide range of sequence complexity. Purified restriction fragments of individual families were used as probes in Southern" transfer and insitu heterologoushybridisations. Most probes hybridised exclusively to the genome of origin, in some cases being confined to the sex chromosomeS. In one instance of interspecific homology between D.yakuba andD.teisseiri, thecommon sequences are arranged in very different and complex patterns. These results indicate the recurrent addition of new families of DNA with the simultaneous elimination (or occasional rearrangement) presumably of once common families in the progenitor genomes. A similar process of concomitant addition/elimination of sequences has occurred for the spacer, coding and insertion elements of the rDNA repeats, generating different rDNA patterns in the species subgroup. The same new arrangement appears to completely replace the old in both the X and Y rDNA clusters of a species, suggesting X/Y sequence interchange. This process is relatively rapid in that discrete differences in the abundance of particular spacer length variants have been found in the ribosome genes of individual X chromosomes of iso-female lines of D.nelanogaster.

PATTERN MOSAICISM FOR BEHAVIOUR IN yellow MUTANTS OF DROSOPHILA MELANOGASTER B. BURNET and R. WILSON Department of Genetics, University of Sheffield and School of Biological and Environmental Studies, New University of Ulster, Coleraine. Mutantalleles at the yellow locus (y—i: 00) differ in their effects on the cuticular pigmentary phenotype. Type-i yellowalleleswhich give full expression on the mutant phenotype throughout the whole cuticle also show behavioural defects including reduced locomotor activity and a low level of male competitive mating success. Type-2 yellowalleles produce pattern mosaics in which some cuticular structures are yellowandothers wild type. The pattern mosaic expression of these alleles extends to behaviour. Type-i mutants show significant differences in catecholamine levels to wild type. The mosaic expression of the type-2 alleles on behaviour may be the consequence of abnormal catecholamine balance in different regions of the nervous system.

GENETICALAND BEHAVIOURAL ANALYSIS OF THE TRACKING BEHAVIOUR OF D. MELANOGASTER R. M. COOK Max-Planck Institute für biologische /(ybernetik, 7400 TUbingen, F.R.G. Thetracking system employed by male D.melanogasterin courtship has been studied using mutants with defective vision and under conditions of illumination beyond the spectral sensitivity of the fly's eye. Degradation of visual processing restricts the velocity at which the female may be tracked and leads to disruption of the control of angular orientation. Females also track other flies, especially other females, and their tracking has been compared with that of males. Episodes of female/female tracking are shorter and slower than those of courtship. Tracking by females can also be distinguished from that by males in the ABSTRACTS 293 positioning of the female around the target, and by the mean maximum distance between them. Females do not allow this distance to increase to that permissible in males. Experiments on the tracking behaviour of genetical mosaics, where male and female visual systems can coexist in the same individual, enable certain of these differences to be attributed to the genotype of the system involved, and point to sex-specific differences in the wiring and/or operation of the fly's visual system.

PYRIMIDINETRANSPORT IN NEUROSPORA CRASSA F. P. BUXTON end A. RADFORD Department of Genetics, Leeds University, Leeds, LS2 9JT Amongmutants of Neurospora crassa selected for resistance to pyrimidine analogues, two classes of uptake mutants have been identified. The first is resistant to 5-fluorouracil, and is defective in pyrimidine base transport across the hyphal membrane. The second is resistant to both 5-fluorouridine and 5-fluorodeoxyuridine, and is blocked in the transport of both pyrimidine and purine nucleosides. Mutants in the former class map at a single locus, uc-5, on linkage group IVR distal to cot-I. Mutants in the latter class represent a second locus, ud-1, on linkage group VIIR between met—7 and arg-10. The pyrimidine base uptake system is known to be controlled by the regulatory gene uc-1 (Williams & Mitchell, J. Bacteriol., 100, 383 (1969)). In addition, it has now been shown that both uptake systems are under nitrogen metabolite repression.

NON-RANDOMDISTRIBUTION OF CLASTOGEN-INDUCED BREAKAGE IN CULTURED MAMMALIAN CELLS B.BRATT Genetics Department, University of Leeds, Leeds, LS2 9J1 Chromosomalaberrations exhibit a non-random distribution. The phenomenon has been studied in many organisms. With chromosome banding techniques it is possible to localise breakpoints with reasonable accuracy. Results have been obtained from studies of the effects of ethyl methane sulfonate, daunomycin, and cytosine arabinoside on human and chinese hamster cell lines. These three compounds stimulate the induction of non-random breakage. These results will be discussed with reference to the different modes of action of the three clastogens and the organisation of chromosome structure, especially the underlying heterogeneity of the DNA as evidenced by the nature of the differential staining.

ANANALYSIS OF THE CLONED GENES FOR THE MAJOR LARVAL SERUM PROTEIN AND THE RIBOSOMAL RNA OF DR OSO PHI LA

ID.M. GLOVER Department of Biochemistry, Imperial College of Science and Technology, University of London. Thelarval serum protein genes are an example of a set of dispersed coordinately regulated genes. We have cloned the genes for the three polypeptide chains of LSP-1 and confirmed the previous cytogenetic location of these genes by in situ hybridisation. Each gene has an intervening sequence near its Send. Nucleic acid hybridisation experiments have enabled us to construct an evolutionary scheme for the divergency of the three genes. Several classes of moderately repetitive DNA which are dispersed throughout the genome are known to be mobile genetic elements. These elements generate sequential duplications at the Sites into which they insert. We have formed a similar sequence duplication at the junctions of the rDNA and its major insertion. This raises the possibility that this insertion is a specialised type of mobile genetic element. The minor type II rDNA insertion occurs at a different site within rDNA and has different structural features at the junctions. 294 ABSTRACTS

PERTURBATIONOF THE SOS RESPONSE OF ESCHERICHIA COLI BY PLASMIDS CARRYING TRUNCATED RECA GENES GEOFFREYYARRINTON AND STEVEN SEDGWICK Genetics Division, National Institute of Medical Research, Mill Hill, London NW7 1AA. Plasmidscarrying recA gene-controlling sequences and adjacent truncated structural genes have been used to study the control of recA gene expression. Such plasmids cause UV sensitization of wild-type Escherichia coli and reduce inducibility of prophage and E. coli mutagenesis. However, induction of chromosomal recA gene expression and genetic recombination are normal. Extensive DNA degradation immediately following irradiation is not observed. Experiments are in progress to distinguish whether these effects are due to the presence of truncated recA proteins or to an excess of recA control sequences.