The Genetical Society of Great Britain

THE GENETICAL SOCIETY OF GREAT BRITAIN

ABSTRACTS of Papers presented at the HUNDRED AND SEVENTY-NINTH MEETING of the Society held on 14th and 15th NOVEMBER 1975 in UNIVERSITY COLLEGE, LONDON.

INTERSPECIES TRANSFER OF MITOCHONDRIA OF PARAMECIUM AURELIA G. H. BEALE and J. K. C. KNOWLES Institute of AnimalGenetics,Edinburgh Thetechnique of microinjection has been used to transfer mitochondria between individuals belonging to different species of Paramecium aurelia, isolated by natural genetic barriers. Mitochondria from three species (denoted nos. 1, 5 and 7) were injected into paramecia belonging to each. Erythromycin-resistant paramecia were used as donors and sensitive cells as recipients, thus making possible a selection of donor mitochondria in the recipients, by adding erythromycin to the medium. Mitochondria from species 1 and 5 could be readily transferred and maintained in all three species, but species 7 mitochondria could be maintained in species 7 cells only. Further- more, species I mitochondria could be established in species 1 cells more readily than in species 5. Hence there are minor differences between species I and 5 mitochondria, and a more pronounced difference between these two and species 7 mitochondria. Study of the transferability of mitochondria from "hybrid" cells, i.e. those containing nuclei of one species and mitochondria from another, gave evidence indicating that the "compatibility" of mitochondria is mainly under the control of the nuclear genome.

CELLSURVIVAL AND CHROMOSOME DAMAGE IN ATAXIA TELANGIECTASIA FOLLOWING X-IRRADIATION A. M. R. TAYLOR, J. A. METCALFE, J. M. OXFORD and C. F. ARLETT Department ofCancer Studies,Medical School, University ofBirmingham and M.R.C.Cell Mutation Unit, University of Sussex, Brighton Ataxiatelangiectasia (AT) is an autosomal recessive syndrome in which a main charac- teristic is an enhanced level of malignant disease. (Kersey, Spector and Good. mt. J. Cancer, 12, 333-347, 1973). Patients given radiotherapy have shown an increased sensitivity to ionising radiation (Cunliffe, Mann, Cameron, Roberts and Ward. Brit. J. Radiology, 48, 374-376, 1975). Cell survival experiments on skin fibroblasts from these patients show that this radiosensitivity is reflected at the cellular level, in all six cases we have studied. Cells from a heterozygote for AT showed normal levels of sensitivity. Investigations into the radiosensitivity of chromosomes of blood lymphocytes from normal controls and AT individuals have revealed: (1) Important differences between these two genotypes following irradiation at the beginning of both Gl and G2; and, (2) Possible anomalies in the accepted classification of chromosome and chromatid type damage induced by irradiation in early Gl and G2 respectively.

AHAPLOIDISATION TECHNIQUE FOR COPRINUS LAGOPUS JANE NORTH Department of Biological Sciences, Cityof London Polytechnic Although stable vegetative diploid strains of Coprinus lagopus are easily selected from common-A heterokaryons, they rarely haploidise even under selective pressure (Casselton, 36/2—s 283 284 GENETICALSOCIETY OF GREAT BRITAIN

Genetical Research 6, 190-208, 1965). The antibiotic griseofulvin is commonly used against dermatophytes and is known to inhibit mitosis in Basidiobolus ranarum by interfering with the spindle apparatus (Gull and Trinci, Arch, Microbial. 95,57-65, 1974). When diploid strains of C. lagopus are grown on medium containing 20 jig/mi griseofulvin, growth is inhibited by 70-80 per cent. More rapidly growing sectors arise after a few days; most when tested appear to be haploids with recombinant genomes. Some sectors remain disomic for the B mating-type locus and may be mitotic recombinants.

THEDOMINANCE INDEX AND IMMUNOGENETIC (IR-GENE) SYSTEMS A. EBRINGER, N. DEACON and C. YOUNG Immunology Unit, Department of Biochemistry, Queen Elizabeth College, London Antigensinjected into different inbred strains of the same species, frequently produce high antibody responses in some strains and low antibody responses in other strains of animals. It has been suggested that this indicates the presence of dominant immune response (IR) genes in high responder animals and their absence in low responder animals (Benacerraf and McDevitt, Science 175, 273, 1972). Genetic degrees of dominance can readily be calculated when examining quantitative phenotypic traits confined to one locus and excluding the effects of pleiotropic and epistatic genes. The degree of dominance (d) was calculated using Fisher's formula (Fisher, Trans. Roy. Soc. Edin. 52, 399, 1918), where, d= Aa—aa —l (AA—aa) and which takes the value of + 1 for complete dominance, —1for complete recessivity and the value of zero for no dominance. In reviewing 875 Fl hybrid animals, obtained from 47 different immunogenetic systems, the degree of dominance (d) was found to be: d =—00284±0Ol48(mean±S.E.) which is close to a value of zero, thus indicating no genetic influence of one allelic JR-gene upon the other, and this lack of dominance is statistically significant (= 2343,p <0.01). Furthermore, Fl back crosses to parental strains give 50 per cent parental response and 50 per cent Fl hybrid response in the backcross progeny. It is suggested that in immunogenetic systems, both alleles are expressed as co-dominant genes.

THEtamA LOCUS IN ASPERGILLUS N!DULANS J. A. PATEMAN and J. R. KINGHORN Deportment of Genetics, University of Glasgow, Glasgow Mutantsdesignated tamArl 19 etc., formerly amrB (Kinghorn and Patema, Heredity, 31, 427, 1973) have been described which are resistant to the toxic analogues thiourea, aspartic hydroxamate, methylammonium and chlorate with L-alanine as the sole nitrogen source. The resistance of tamAr mutants is correlated with partially repressed levels of some enzyme and transport systems regulated by ammonium. Furthermore, lamAr mutants have low NADP-glutamate dehydrogenase activity and also efflux ammonium under certain conditions. This mutant isolation method also generated partially repressed mutants at the areA locus (Arst and Cove, Molec. gen. Genet., 126, 111-141, 1973). A fully repressed allele of tamA has been made (tamAt50). It is unable to utilise a number of inorganic and organic nitrogen sources and grows normally only on ammonium. A revertant of tamA' was selected on the basis of sensitivity to the toxic analogues in the presence of ammonium. This derepressed allele, designated tamA4l, is insensitive to ammonium control of a number of ammonium repressible systems. GENETICAL SOCIETY OF GREAT BRITAIN 285

The properties of the various tamA alleles establish that tamA is a regulatory gene involved in the control of nitrogen and/or carbon metabolism in A. nidulans.

THENEWBORN SCREENING BLOOD SAMPLE: A VALUABLE SOURCE OF GENETIC DATA IN MAN P. S. HARPER and L. K. BORYSEWICZ Section of Medical Genetics, Department of Medicine, Welsh National School of Medicine, Cardiff Inall regions of Britain and in most of continental Europe a capillary blood sample dried on filter paper is taken from all newborn infants for the detection of phenylketonuria. This sample represents a potentially valuable source of population data on polymorphic genetic markers, and a study has been made in Wales to assess the feasibility of using it to obtain population frequencies for blood group and red cell enzyme systems. The results for the ABO blood group system and for the enzymes PGM 1 and AK show close correspondence with phenotype frequencies obtained from conventional samples and methods; the sample is less suitable for some other loci which may not be fully expressed in the newborn period. The application of this approach to studies of genetic variation between and within populations, and to the prospective study of the selective advantage of genetic polymorphic systems, will be discussed.

GENETICHETEROGENEITY AND VARIATION OF ENZYME ACTIVITIES IN PRIMARY AND TRANSFORMED CHINESE HAMSTER CELL LINES J. M. CLARK and J. A. PATEMAN Institute of Genetics, University of Glasgow, Glasgow Gil Sf5, Scotland Theactivities of nine enzymes have been studied in cultured Chinese hamster Kupifer cells. The Kupifer cell population in liver provides a source of homogeneous cells which express "differentiated" functions in culture. Isolated Kupifer cells from three adult, female sibs were used to initiate 130 cell lines, each originating from a single Kupifer cell. The following enzyme activities were studied: peroxidase, catalase, fl-glucuronidase, arginase, haem oxygenase, alcohol dehydrogenase, lactate dehydrogenase, isocitrate dehydrogenase and glucose-6-phosphate dehydrogenase. Each enzyme demonstrated considerable variation in activity between cell lines. In all cell lines, enzyme activities dropped below the initial level and maintained a minimum activity for approximately 80 cell doublings. Hetero- geneity of enzyme activities was not paralleled by karyotypic variation. Transformation of cultured adult Kupifer cell with Simian Virus 40 resulted in the loss of "differentiated" functions, and all enzyme activities, with the exception of fl-glucuronidase, fell to a fraction of those observed in primary adult cell lines. Unlike cultured Kupifer cells from adults, cultured foetal Kupifer cells exhibited many of the properties of transformed adult Kupifer cells. The observation of a high correlation between certain enzyme activities in cultured adult cells suggests the possibility of a mechanism which controls the activities of two or more unrelated enzymes. These correlations are maintained in cultured foetal cells but are disrupted in cultured transformed cells. The large variation in enzyme activities between cell lines initiated from identical material and grown under standardised conditions suggests caution in the interpretation of data obtained from small numbers of cell lines. 36/2_s* 286 GENETICAL SOCIETY OF GREAT BRITAIN

REQUIREMENTFOR A FUNCTION OF DNA POLYMERASE III IN ULTRAVIOLET-LIGHT MUTAGENESIS IN ESCHERICH!A COLI B. A. BRIDGES and R. P. MOTTERSHEAD MRC Cell Mutation Unit, University of Sussex S. G. SEDG WICK Brookhaven National Laboratory ThepoiC temperature-sensitive DNA polymerase III mutation from Escherichia coil BT1026 has been transduced into E.coli WP2 (to give CM731) and WP2 uvrA (Hill) (to give CM741). In CM73 1, UV lesions capable of leading to Strr mutations disappeared during post-irradiation incubation at restrictive temperature and did not lose photoreversibility in contrast to the result at permissive temperature where mutations progressively became non-photoreversible. In CM741 photoreversibility ceased to be lost immediately upon transfer to restrictive temperature whereas post-replication repair strand joining still occurred and uptake of 5H-thymidine into DNA continued for 20 to 30 mm. It is concluded that a function of the poiC gene is necessary for error-prone repair to operate and that this function is defective in the enzyme specified by the poiC allele from BT1026. This particular function is not required for most post-replication repair of strand gaps or for normal DNA replication, at least over periods of time up to 20 mm. It is suggested that the defect may lie in a site of the DNA polymerase III molecule that is involved in interaction with a co-factor (possibly inducible) able to overcome the normally high specificity of the polymerase and allow it to insert incorrect bases opposite pyrimidine dimers.

FUNCTIONALCOMPLEXITY IN THE PYR-3 LOCUS OF NEUROSPORA CRASSA A. J. MAKOFF and A. RADFQRD Department of Genetics, University of Leeds, Leeds LS2 9JT Thepyrimidine-3 locus specifies two enzyme activities, pyrimidine-specific carbamyl phosphate synthetase (CPSpyr) and aspartate transcarbamylase (ATC). ATC is trans- lationally distal. CPSpyr, but not ATC, is subject to feedback inhibition by UTP. To investigate the location of the feedback-specific regionwithin the locus, inhibitionofa number of pyr-3 alleles by UTP was investigated. All CPSATC- polar alleles, revertants of CPSATC- polar alleles, and 5- fluorouracil-resistant mutants had normal UTP response. One Out of five CPSATC+ alleles had reduced UTP-sensitivity, suggesting that the location of the feedback-specific region is in or close to the CPS-specific region. As glutamine-dependent CPS activity in other organisms is composed of a glutaminase and an ammonium-dependent CPS, CPSATC+ mutants in Neurospora were examined for glutamine- and ammonium-dependent CPS activities. No evidence was found that these two functions were separable.

INDUCEDRECIPROCAL TRANSLOCATION OF AN A AND B CHROMOSOME IN LOLIUM PERENNE G. M. EVANS and A. i. MACEFIELD Department of Agricultural Botany, University College of Wales, Aberystwyth Bchromosomes are known to have a marked effect on chromosome pairing in interspecific crosses of Lolium. The effect is such that association of homoeologous chromosomes is largely suppressed but that of homologous chromosomes is unaffected (Evans and Macefield, JTature X.B. 236, 100-111; Chromosoma 41, 63-73). The use of B's in stabilising artificial polyploids is ruled out however by their tendency to accumulate in populations through a system of directional non-disjunction at pollen grain mitosis. Translocation of B chromosome material into the normal A complement was considered a possible solution. X-ray treatment of heads of 2B Lolium perenneplantsproduced transloc- ations involving both the A and B chromosome. One translocation (Y7) was subsequently identified as reciprocal and involved a small terminal segment of an A chromosome and most probably the complete short arm of the B. Preliminary assessment of the affect of this trans- GENETICAL SOCIETY OF GREAT BRITAIN 287 location on homoeologous pairing in Loliam temulentum x Loliurn perenne hybrids seems to indi- cate that pairing Control is quantitative in nature.

RESTRICTIONENDONUCLEASE TECHNOLOGY N. M. WILKIE Institute of Virology, University of Glasgow, Church St., Glasgow Gil 5JR Scotland Theterm "restriction endonucleases" refers to two different types of DNA specific endonucleases which were first observed during studies on host mediated restriction and modification of bacteriophage. The impact of these enzymes on molecular biology and genetics has been dramatic. Both kinds of enzyme system recognise specific sequences in double helical DNA. Class 1 enzymes may cause double strand cleavages at positions remote from the recognition sites or may modify the recognition site and protect the DNA from further endonucleolytic attack. Since the cleavage products tend to comprise a variable collection of fragments from the original DNA, this class has not been widely used by geneticists or molecular biologists. However, Class 2 enzymes cleave double stranded DNA at the specific recognition site (almost invariably the sequences recognised are "palindromic") to generate reproducible, defined fragments, and have brought about profound changes in the way in which we think about problems in molecular biology and genetics, and in our ability to solve them.

MAPPINGOF THE GENOMES OF POLYOMA AND SV4O VIRUSES BEVERLEY E. GRIFFIN Imperial Cancer Research Fund, P.O.B. 123 Lincoln's Inn Fields, London WC2A 3PX Inthe decade or so since their discovery, the two papova-viruses, polyoma and Simian Virus 40 (SV4O), have received considerable attention mainly due to their oncogenic properties. The belief generally held is that an understanding of the interaction between these viruses and susceptible cells which brings about the phenomenon called cellular transformation will lead to an understanding of how viruses cause cancer (if in fact viruses do cause cancer). Polyoma and SV4O are both small viruses which carry their genornic information in their DNA. The DNA is 3-4 x l0 daltons in size (with enough information to code for about 200,000 daltons of protein) and can be isolated in a closed-circular, superhelical form. Before the discovery of restriction endonucleases, a definition of the genetics of these viruses seemed remote largely because of the low frequency of recombination, the small number of available mutants, and the lack of suppression systems comparable to those used in studying the bacterial viruses. The study of the action of restriction endonucleases has however resulted in the elucidation of physical maps both for polyoma and SV4O DNA's. The physical maps have subsequently been used to study transcription and translation of wild type viral DNA, to map some of the available mutants, to place biological markers (for example, the origin and termination of DNA replication) on the genome, to define strain differences and to study defective viral DNA's. Restriction enzyme fragments have been used to transform cells but as yet no con- vincing data relevant to transformation are available.

MAPPINGOF THE GENOMES OF ADENOVIRUS TYPES 2 AND 5 AND RECOMBINANT MOLECULES JIM WILLIAMS M.R.C. Virology Unit, Institute of Virology, Church Street, Glasgow Gil SiR Theadenovirus genome is a linear duplex of DNA and depending on the serotype examined this DNA has a molecular weight within the range 20-23 x l0 daltons, which is potentially sufficient genetic information to code for some 25-40 polypeptides of average size. 288 GENETICAL SOCIETY OF GREAT BRITAIN

The DNA is neither circularly permuted nor terminally redundant, but single strands form circles because each strand bears inverted terminal repetitions. In order to understand the regulation of adeno gene expression during infection, it will be necessary to build up a clear picture of the detailed organisation of the adenovirus genome. Recent application of new technologies has brought about considerable progress in determining the location of virus genes on the adeno chromosome, and in this paper some of the work carried out in various laboratories during the past two years is reviewed under the following headings: (1) Physical mapping of adeno DNA with restriction endonucleases. (2) Classical genetic mapping of temperature-sensitive and other mutations. (3) Physical mapping of ts mutations—alignment of genetic and physical maps and location of fibre and hexon genes. (4) Mapping early and late viral-specific RNA on the adeno genome. (5) Mapping adeno genes by cell-free translation of RNA selected by hybridisation to specific DNA fragments. (6) Locating the adeno transforming gene(s).

THEPHYSICAL STRUCTURE OF THE HERPES SIMPLEX VIRUS GENOME J. B. CLEMENTS Institute of Virology, University of Glasgow, Church St. Glasgow Gil SJR Fromelectron microscopic observations on intact single-stranded DNA of herpes simplex virus type I (HSV-I) before and after self reassociation Sheldrick and Berthelot (1974) suggested that the HSV-I genome consisted of two unique regions each flanked by redundant sequences which were inverted relative to each other. As terminal redundancy also has been reported for HSV-I DNA (Sheidrick and Berthelot, Cold Spring Harb. Symp. Quant. Biol. 39, 667, 1974; Grafstrom et al., Cold Spring Harb. Symp. Quant. Biol. 39, 679, 1974) some common sequences may be present in each redundant region. Inherent in this genome configuration is the possibility that either terminal repeat can pair with its internal com- plementary sequence. Assuming this pairing then, as suggested by Sheidrick and Berthelot, a reciprocal recombination event will result in the inversion of the entire unique sequence between the participating repeats. On the basis of restriction endonuclease analysis of HSV-I and HSV-2 DNAs with the Hind III, Hpa I and Eco RI enzymes, and on hybridisation experiments with isolated fragments, we have identified four forms of the herpes virus genome in which the unique sequences are relatively inverted. The results suggest also that the sequences present in each redundant region are not identical. Current allocations of restriction enzyme fragments on the physical map of the genome are presented and the consequences of such a novel genome for studies on HSV recombination considered.

RESTRICTIONENZYMES AND THE CLONING OF DNA IN BACTERIOPHAGE A NOREEN E. MURRAY Department of Molecular Biology, University of Edinburgh, Mayfield Road, Edinburgh EH9 3JR Somerestriction endonucleases, in particular EcoRI and Hindill, break duplex DNA's into fragments with short cohesive ends. The DNA of bacteriophage A has five targets for EcoRI and six for Hindill but any, or all, of these targets, can be removed. Since the central region of the A chromosome, that is over a third of its DNA, is inessential for plaque formation this region may be sacrificed to provide space for other DNA. Phages having only a single target for EcoRI or Hindlil, or phages which have their only targets flanking the non- essential region of the chromosome serve as receptors for fragments of DNA made by digestion with the appropriate restriction enzyme. These fragments may be covalently attached to the restricted phage DNA with polynucleotide ligase and the recombinant molecules recovered in plaques following transfection of E. coli. with the products of the ligase reaction The current understanding of the genetics and biochemistry of phage A has permitted the development of simple methods for the screening and selection of those phages that carry GENETICAL SOCIETY OF GREAT BRITAIN 289 additional or substituted sequences. In addition, the phage system may be further exploited to facilitate, or maximise, the expression and genetic analysis of the heterologous DNA and in the design of vectors with a very limited host range.

PLASMIDSAND VIRUSES AS VECTORS IN DNA CLONING E)PERIMENTS DAVID SHERRATT School of Biological Sciences, University of Sussex, Falmer, Brighton BNI 90G

BacteriophageA and a number of different plasmids are currently being used as vectors for the cloning in Escherichia coli of DNA fragments from a variety of sources. The relative properties of these and other possible vectors will be discussed with reference to those of an "ideal vector". Such a vector should be selectable both alone and when containing inserted DNA sequences; these forms of the vectors should be distinguishable ideally by selection. In some situations one may be able to select, or greatly enrich for vectors containing specific DNA sequences. A vector should be efficient in amplifying inserted DNA and where possible should allow expression of inserted DNA, either from promoters within the insert or from the vector itself; in the latter case it may be desirable to utilise "strong" promoters. Vector and host should also be designed to minimise the possible hazards from accidental "escape" of the vector and for host. Some recent results from DNA cloning experiments will also be described, as will some of the potential applications of these types of experiments.

RAPIDRESTRICTION ENZYME FRAGMENT MAPPING IN BACTERIOPHAGE cPXI74 DNA P. M. SLOCOMBE MRC Laboratory of Molecular Biology, Cambridge Apulse-chase method (Jeppesen and Sanders, personal communication) has been used to map bacteriophage X 174 DNA restriction enzyme fragments. 'IXl 74 has a single strand genome of approximately 5500 bases and replicates via a double-stranded intermediate replicative form (RF). Restriction enzyme fragments from IsXl74 RF are isolated by gradient acrylamide gel electrophoresis and numbered according to their relative size. Each fragment is then annealed to the template single strand DNA and this is used as a primer for DNA polymerase I in the presence of the four deoxyribonucleoside triphosphates, one of which is {c-32P] -labelled. Synthesis is allowed to proceed for a short time and then the labelled triphosphate is "chased out" with unlabelled triphosphate and the reaction continued. The extended primer-template complex is then cleaved with the appropriate restriction enzyme and the products refractionated on a gradient acrylamide gel. In this way only the fragment adjacent to the 3' end of the primer is labelled. Thus the relative order of the restriction fragments can be easily and rapidly determined. Restriction enzyme maps of cIX 174 DNA of Haernophilus haemo(yticus (Hha I), Art hrobacter luteus (Alu I) and Haemop/zilus aphrophilus (Hap II) have been established and aligned with respect to each other and to known Hind II and Hae III maps.

ANUCLEASE WHICH PREFERENTIALLY INACTIVATES DNA CONTAINING A SINGLE MISMATCHED BASE PAIR A. AHMAD Max-Planck Institut fur Molekulare Genetik, Berlin, W. Germany W. K. HOLLOMAN and R. HOLLIDAY National Institute for Medical Research, Mill Hill, London Itis widely accepted that hybrid or hetero duplexDNA is an intermediate in genetic recombination. In heterozygous crosses, hybrid DNA may contain one or more mismatched 290 GENETICAL SOCIETY OF GREAT BRITAIN

base pairs, and it was suggested some years ago that gene conversion could be due to the repair of these. Strong genetic evidence for repair of this type has subsequently been obtained in several micro-organisms. A search for an enzyme which might recognise mismatched bases in DNA was initiated by the isolation of DNase deficient mutants in the fungus Ustilago maydis. Some of these were shown to be deficient in the process of gene conversion and also to have a low level of a nuclease, DNase I (Badman, Genet. Res. 20, 213, 1972; Holloman and Holliday, J. Biol. Chem. 248, 8107, 1973). This enzyme is primarily active on denatured DNA, but it will introduce nicks in native DNA, especially if this has been irradiated with UV light. The DNA strands of bacteriophage SPPI can be separated by density centrifugation and, by annealing mutant and wild type strands, molecules containing a single mismatched base pair or a deletion can be obtained (Spatz and Trautner, Molec. Gen. Genet. 109, 84, 1970). Using the transfection assay with Bacillus subtilis, we have now demonstrated that hetero- duplices are more rapidly inactivated by DNase I than are homoduplices. It is known that a single nick is sufficient to destroy the biological activity of transfecting DNA, but it is not yet known whether the recognition of a single mismatched base pair DNase I involves the cleavage of one strand at the mispaired region.

RESTRICTIONENZYME ANALYSIS OF THE EARLY REGION OF BACTERIOPHAGE T7 R. L. GORDON, P. HUM PHRIES and D. McCONNELL Department of Genetics, Trinity College, Dublin, Lire TheDNA of bacteriophage T7 has been cleaved by a number of restriction enzymes. The sizes of the fragments produced by each enzyme have been determined. DNA from early region deletion mutants of Ti which have previously been mapped by electron microscopy (Simon and Studier, J. Mol. Biol., 79, 237, 1973) were also digested by these restriction enzymes. By examination of the changes in the banding patterns, fragments originating from the early region could be identified and their order determined.

THEMUTATIONS SEX REVERSAL (SXR) AND TESTICULAR FEMINISATION (TFM) IN THE MOUSE AND THE INDUCTION OF ENZYMES BY OESTRO- GEN AND TESTOSTERONE GRAHAME BULFIELD Institute of Animal Genetics, University of Edinburgh, West Mains Road, Edinburgh Themutations Sxr and Tfm reverse some sexual characteristics in the mouse. Sxr changes females to males (Cattanach et al. (1971) Cytogenics, 10, 318) and Tfmchangesmales to females (Lyon and Hawkes (1970) Xature 227, 1211). Ohno and Lyon (1970, Gun. Genet. 1, 121) have proposed that Tfm is a repressor non-inducible mutation of the regulatory locus that mediates response to testosterone. Several enzymes differ in activity between the sexes, including the histidine catabolic enzymes. We have investigated the effect of Tfm and Sxr on (a) the activity of those enzymes and on (b) the induction or repression of those enzymes by oestrogen or testosterone.

DNAVARIATION IN LATHYRUS R. K. J. NARAYAN and H. REES Department of Agricultural Botany, University College of Wales, Aberystwyth Inthe genus Lathyrus the divergence and evolution of species was accompanied by large- scale changes in nuclear DNA amount. All the species are diploids with 14 chromosomes GENETICAL SOCIETY OF GREAT BRITAIN 291 so that the DNA changes were the result of amplification or deletion of segments within chromosomes. Our evidence indicates that the quantitative changes involve mainly the repetitive, as distinct from the non-repetitive fraction of the chromosomal DNA and, on a cytological basis, mainly heterochromatin in contrast to euchromatin. There is an element of discontinuity in the distribution of DNA amounts among species which suggests that the DNA variation results from a series of separate, spasmodic events. The discontinuities may be viewed, also, as "steady states" from the standpoint of genetic balance and biological fitness.

HUMAN2M AND HLA ARE EXPRESSED INDEPENDENTLY ON INTERSPECIFIC HYBRIDS E. A. JONES, P. N. GOODFELLOW, R. KENNET, S. POVEY and W. F. BODMER Genetics Laboratory, Department of Biochemistry, University of Oxford Directcytotoxicity and absorption analysis were used to detect HLA antigens on man! mouse somatic cell hybrids. Confirmation of the assignment of the Major Histocompatibility Complex to chromosome 6 was obtained. The same series of hybrids was used to study the interaction between HLA and fl2m on the cell surface. Results obtained from a series of clones indicated that there was complete independence of expression of HLA and fl5m. Human 2m was found to be unnecessary for the normal serological expression of HLA suggesting that mouse fl2m could possibly replace human 2m as a subunit of the HLA molecule. Further investigations using lysostrip experiments are being carried out in an attempt to confirm this. Heteroantisera to human 2m and alloantiserum to HLA-A2 were used, together with complement, to selectively remove the chromosomes coding for 2m and HLA from a hybrid clone. Manipulation of the karyotype in this way further confirmed the independence of HLA and 5m on somatic cell hybrids.

ISOCITRATELYASE CONSTITUTIVE MUTANTS IN ASPERGILLUS NIDULANS W.McCULLOUGHand C. F. ROBERTS Department of Genetics, University of Leicester Revertantsof pycA (pyruvate carboxylase-less) strains selected for growth on sucrose agar plates were screened for constitutive formation of isocitrate lyase using a "spot test" for enzyme activity in sucrose grown mycelium in liquid microcultures. The first four constitutive strains analysed are complex; three contain genetic suppressors of the pycA lesion in addition to an isocitrate lyase constitutive (ide)mutation.The four idle mutations have been recombined into otherwise wild type strains which grow normally on all carbon sources tested. Three of the mutations are allelic and recessive in heterozygous diploids and the fourth is partially dominant; the four mutations define two regulatory loci, one (ideA) in linkage group IV and the other (icleB) in linkage group I. They are therefore not linked to the structural gene for isocitrate lyase (acuD),linkagegroup V. Although single id0 mutations cause the formation of low constitutive levels of enzyme activity (approximately 5 per cent fully induced wild type) the double mutant at both loci (id0A; iclcB) contains a high constitutive level of activity (approximately 25 per cent fully induced wild type). We propose a model for the genetic control of isocitrate lyase based on an interaction between the products of the two regulatory loci.

THEREGULATION OF GLUTAMINE TRANSPORT IN WILD-TYPE AND MUTANT STRAINS OF SALMONELLA TYPH!MURIUM P. R. BETTERIDGE and P. D. AYLING Unit of Genetics, Department of Plant Biology, The University, Hull

Esc/serichiacoli, grown on high levels of ammonium as the sole nitrogen source, has greatly reduced glutamine synthetase activity compared with cultures grown on limiting sources of