2003 Volume 31 Issue 3 Pages 201-214
We have previously proposed a hypothesis on the origin of genes, suggesting that genes generally originated from nonstop frames on antisense strands of GC-rich genes (GC-NSF(a)s) under the universal genetic code [Ikehara, K., et al., Nucl. Acids Res., 24, 4249 (1996)]. To obtain evidence for the hypothesis, simulation of gene evolution was carried out under the six conditions for folding of polypeptide chains into appropriate three-dimensional structures using a Mycobacterium tuberculosis GC-NSF(a) (508 codons) as an ancestor gene. The results showed that the simulation well reproduces both the base compositions at three codon positions and the average amino acid compositions of extant proteins encoded by microbial genomes when a conserved region (200 codons) in simulated proteins was set at about 40%. Contrary to that, the guanine composition at the first codon position and the average amino acid compositions considerably deviated from those of extant genes and proteins when the simulation was carried out using a Borrelia burgdorferi AT-rich gene as an ancestor gene in the presence or the absence of about 40% conserved regions. These results apparently support the GC-NSF(a) hypothesis on the origin of genes which we have proposed.
