The periodic variations obtained by correlating -the relative positions of.purines and pyrimidines (and of the four bases thymine, cytosine, adenine, and guanine) in. a wide variety of genomes of wholly or partly known sequence suggest that there may be enough of an earlier comma-free coding system (i.e., only readable in one frame) still present to permit determination of the reading frame and approximate extent of the present protein coding stretches. The characteristics of these variations support the hypothesis that these primitive messages were formed of coding triplets having the form RNY (R = purine; Y = pyrimidine; and N = purine or pyrimidine). The base sequences and reading frames that have a minimal deviation from such a message are still good predictors of actual coding regions and reading frames in spite of the many. mutations that have occurred since such a genetic code was last in use. In fact, the right frame for almost all the proteins in a number of viruses and various prokaryotes and eukaryotes is deduced purely from purine/pyrimidine information and.not by using the normal start and stop signals.The concept of a comma-free genetic code was first discussed by Crick et aL (1) in 1957 when the form of the code was still unknown. A messenger strand was envisaged in which the triplets ("sense" codons) of a message in one reading frame could not be found anywhere among the triplets in the other two frames ("nonsense" codons). It was shown that a maximum of 20 different sense triplets could be used in such a system, but the idea was abandoned when found not to conform with the actual coding system with its start and stop signals and the use of degenerate codons. More recently, however, Crick et al (2) have considered a possible primitive means of protein synthesis in the absence of ribosomes and using only a messenger strand and a few primitive tRNAs, each having two possible conformations (3, 4). With this hypothesis and using data on the sequence regularity in the anti-codon loops of present day tRNAs, they deduced that a primeval message should conform to the pattern of purines (R) and pyrimidines (Y) RRY RRY RRY .... Subsequently, Eigen (5) further considered this concept and found that an RNY (N = purine or pyrimidine) message (i.e., a mixture of RRY and RYY codons) would also fit the tRNA data and the protein synthesis hypothesis and would have several advantages over an RRY message, particularly the better balance between the numbers of R and Y and the symmetry between the plus and the minus strands. Both of these messages are clearly comma-free codes, but now in the simpler sense that they function solely by distinguishing between R and Y rather than among thymine, cytosine, adenine, and.guanine as earlier considered (1). Rhythmic correlationsTo understand the evidence for remnants of a comma-free code, it is necessary to describe briefly the main features of the strong R,Y rhythmic correlations with a period of three bases that have been found, with the help of a computer, in the c...

Homoeotic genes in the bithorax and Antennapedia complexes of Drosophila melanogaster appear to specify the developmental fate of segments of the fly. Some of these genes (Ultrabithorax, Antennapedia and fushi tarazu) share homology due to their conservation of a 'homoeo domain'1,2 consisting of 60 amino acids. Cross-hybridization and cloning experiments show that the homoeo domain is conserved in a frog (Xenopus laevis) gene expressed in early development and may also be present in earthworm, beetle, chicken, mouse and human genomes. The extreme conservation found in the amino acid sequences between the Drosophila and Xenopus domains suggests that the domain has a vital function in the control of early development. Here we report the results of a search made in the Dayhoff sequence bank, which reveals a lesser but apparently significant homology between the homoeo domain and the amino acids coded from parts of the a 1 and alpha 2 mating type genes of the yeast Saccharomyces cerevisiae.

The DNA sequence of a new IS element, the IS26, is 820 bp long and carries 14 bp perfect terminal inverted repeats. Upon integration, IS26 generates an 8 bp duplication of its target sequence. A large open reading frame within IS26 could code for a protein of 234 amino acids. On its reverse strand, IS26 also carries one large open reading frame, 591 bp long, which contains no stop codon within IS26.

In Drosophila melanogaster, the decrease in protein synthesis that accompanies aging Is preceded by a decrease in elongation factor EF-la protein and mRNA. Here we show that Drosophila transformed with a P-element vector containing an EF-la gene under control of hsp7O regulatory sequences have a longer life-span than control flies.TATAA NotI AATAAA (Fig. la).Comparative measurements of mean lifetime for male flies were made under carefully controlled conditions (see Fig. 2 legend), always using a sample of 100 newly hatched flies and counting the survivors each day. The first observation made was that the ry+ control strains C had much longer lifetimes than the ry5 mutant. Evidently the lack of xanthine dehydrogenase coded by the rosy locus, although not lethal to the flies, has a strong negative effect on their viability. Second, the E strains with the additional EF-la gene were observed at 250C to have on average a significantly longer lifetime than the control strains C (P < 0.001), but there were variations in lifetime between the individual lines of the C and E strains. These can be understood in terms of different positions of P-element insertion into the genome, possibly mutating a nonessential gene or encountering transcriptional enhancing effects from neighboring genomic sequences. It is also possible that some genetic background differences affecting viability could derive from the balancer strains used. These effects were eliminated from a detailed comparison between the C and E strains by taking two specific lines, C3 and E4, and comparing their relative lifetimes at 25TC and 29.50C. Insertion positions and genetic background then remain unaltered in the comparison and only the effect of additional transcription of the EF-la gene at 29.50C should be seen. (By hybridization on polytene chromosome squashes these insertions were seen on the third chromosome at positions 65A and 79F, respectively, for the C3 and E4 flies. The structure *Pressent address: Cell and Molecular Biology Laboratory, University of Sussex, Brighton BN1 9QG, England. tPresent address:

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