540 Nature Vol. 288 11 December 1980 been cloned in Stanford and is being used base pair substitution in this region and by premature transcription; but that these for the analysis of this entire region of the a factor of two in the abudance of their early transcripts are not translated and, genome by S. Beckendorf (University of mRNAs. indeed, decay as development gets under California, Berkeley) and for detailed The egg shell protein genes, under study way. Only at the appropriate develop­ studies of the gene itself by M. Muskavitch by A. Spradling (Carnegie Institution, mental stage several hours later does (Stanford). A surprising result is that the Washington) and in F. C. Kafatos' transcription resume to produce mRNAs transcript of SGS-4 differs in size in laboratory (Harvard) also surprised us for that are subsequently translated. different strains of Drosophila. This they are amplified in the tissue in which What is the meaning of this? It implies results, it would appear, from the fact that they are expressed. Spradling has found some relationship between amplification within the coding sequence there is a 21 that the amount of DNA amplified extends and early transcription and also indicates base pair sequence whose repetition at least 30 kb on each side of the genes the existence of a translational control at frequency can vary between different themselves, but the degree of amplification the early developmental stage. SGS-4 alleles. Although nothing is known falls off, from a peak of some 60 fold, in Like all good meetings, at the end there of the chemistry of the protein this must both directions away from the coding were far more questions than answers. As is reflect a sequence of seven amino acids sequences. This, and the fact that the right and proper we were treated to many repeated a varying number of times. amplified DNA has an identical restriction very preliminary data whose place in the The mutation characterised by Korge, pattern to non-amplified DNA, may jigsaw puzzle is yet undiscovered. The that fails to make SGS-4 protein when indicate that the process is chromosomal, great success oft he Kolymbari meeting was homozygous turns out to be a small rather than extra-chromosomal as in in bringing together molecular and classical deletion, but of a sequence over 200 base oocyte ribosomal genes in many Drosophila biologists to discuss their data pairs away from the 5' end of the messenger organisms. Yet the Harvard laboratory (G. from their different perspectives and we RNA. The importance of this region is Thiroes and R. Griffin-Shea) have found can only hope that some of today's indicated by the fact that two different that amplification of another pair of egg mysteries will be clearer to us when we next expressed alleles of SGS-4 differ by a single shell protein genes is accompanied by their meet. I. Comets and the origin of life from N.J. McNaughton and C. T. Pillinf!,er COMETS are the most spectacular bodies in possible end preduct of a fragment of await the eventual laboratory analysis of our solar system and the anticipated return protosolar nebula collapsing in a relatively cometary material. The identification of of Halley's Comet in 1985-6 has already low magnetic flux. According to the same microscopic stratospheric and deep-sea proved a catalyst for increased cometary theory, planetary systems would be particles of extraterrestrial origin by research. As the comet nucleus contains, produced in a large magnetic flux and there Brownlee (University of Washington) perhaps with the exception of phosphorus, seems to be no way for both planets and offers, however, the first real samples of the necessary ingredients for life on this comets to be produced together. probable cometary debris. The minute size planet, the pundits of eathbound chemical The current interest in comets has and rarity of unaltered Brownlee particles evolution and cometary science found promoted a shift in emphasis among the preclude the use of most conventional common ground at a recent colloquium* prebiotic synthesis investigators - low analytical procedures, and substantial entitled 'Comets and the origin of life'. temperatures and photon or proton refinements to existing or even new Although almost all of our observations irradiation appear to be the order of the techniques (such as the CD4 carbon of comets have been obtained from or near day. Reproducing cometary compositions isotopic method pioneered at the the Earth, the accumulated data yields a and environments in the laboratory, the University of Cambridge), are required basic understanding of the structure, Maryland group and Greenberg (Leiden before even the Brownlee particles can be chemistry and physics of the comet nucleus University, Netherlands) have synthesised fully exploited. and tails. Perhaps the most significant 'life-like' organic molecules. Long chain The alternative to analysing cometary point to emerge from new observations is hydrocarbons, nitrogenous compounds material found in the terrestrial the apparent constancy of comet's and carboxylic acids have been identified environment is in situ measurements from chemical composition. spectroscopically among the products of spacecraft. The planned NASA/ESA A'Hearn (University of Maryland) reactions carried out at temperatures as low international mission to rendezvous with observed that the rate of production of as l5°K. Given that similar molecules Halley's Comet which would have allowed certain chemical species, particularly CN, could only be produced on the Earth under analyses as sophisticated as those needed C2, C3 and OH, from the comet nucleus a strongly reducing protoatmosphere for origin of life studies will now not near the sun is uniform irrespective of the (which the Levine group from Virginia take place. ESA's fast flyby of Halley (the type of comet and its gas to dust ratio. The calculate would be short-lived due to the Giotto mission) will undoubtedly produce spectroscopic continuums of comets of high reactivity and abundance of OH), the information on the composition of the gas different ages are also strikingly similar introduction o1 such molecules via comets and solid phases to fuel further laboratory (Donn, NASA-Goddard). It is not yet clear into a less drastic protoatmosphere offers a based studies but is unlikely to provide whether this uniformity is due to the nature real, and in some cases preferred, definite answers to the question of whether of the chemical reactions in the coma or if it mechanism for the beginning of life on comets were involved in the origin of life on implies that comets are derived from a Earth. Speculations on this theme range Earth. constant composition reservoir. How the from the controversial- Wickramnsinghe latter interpretation fits with a recently (University of Cardiff) envisaging comets CORRIGENDUM announced theory for the origin of comets as the carriers of already living organisms Edward Herbert would like to point out that (Biermann Royal Society Meeting on - to efforts to calculate possible mass he was not the sole author of Biosynrhesis and Planetary Exploration, Munich, Nov. 4-5, inputs (Lizcano-Aranjo, Houston). processing of cellular and viral polyproteins 1980) is not clear. Biermann's new Definitive evidence on the relationship (News and Views, 13 November, 288, 115, hypothesis predicts cometisimals as the between comets and the origin of life must 1980) and would like to acknowledge the co­ authorship of Gunther Kreil (Salzburg) and N.J. McNaughton and C. T. Pillinger are in the the help of Carolyn Carter and Eckard •The Fifth College Park Colloquium on Chemical E\·olution Department of Earth Sciences, University of was organized by Cyril Ponnamperuma and held at the Wimmer (Stoneybrook, New York). CambridJ:w. University of Maryland. Oct 29·31, 1980. 0028-0836/ 80/ 500540.01$01 .00 .