Cebrat S, Mackiewicz P, Dudek M R
Institute of Microbiology, Wrocław University, Poland.
Biosystems. 1998 Feb;45(2):165-76. doi: 10.1016/s0303-2647(97)00072-5.
The genetic code has a very interesting property--it generates an open reading frame (ORF) inside a coding sequence, in a specific phase of the antisense strand with much higher probability than in the random DNA sequences. Furthermore, these antisense ORFs (A-ORFs) possess the same features as real genes--the asymmetry in the nucleotide composition at the first and second positions in codons. About two thirds of the 2997 overlapping ORFs in the yeast genome possess this feature. Thus, the question arises: has this feature of the genetic code been exploited in the evolution of genes? We have searched the FASTA data bases for homologies with the antisense translation products of a specific class of genes and we have found some sequences with relatively high homology. Many of them have scores which could be randomly found in the searched data bases with a probability lower than 10(-6). We conclude that some genes could arise by positioning a copy of the original gene under a promoter in the opposite direction in such a way that both, the original gene and its copy initially use the same nucleotides in the third, degenerated positions in codons.
遗传密码具有一个非常有趣的特性——它在编码序列内、反义链的特定相位产生一个开放阅读框（ORF），其概率远高于随机DNA序列。此外，这些反义ORF（A-ORF）具有与真实基因相同的特征——密码子第一和第二位核苷酸组成的不对称性。酵母基因组中2997个重叠ORF中约三分之二具有这一特征。因此，问题来了：基因进化过程中是否利用了遗传密码的这一特性？我们在FASTA数据库中搜索了与特定一类基因的反义翻译产物的同源性，发现了一些具有较高同源性的序列。其中许多序列的得分在搜索数据库中随机出现的概率低于10^(-6)。我们得出结论，一些基因可能是通过将原始基因的一个副本以相反方向置于启动子之下而产生的，这样原始基因及其副本最初在密码子的第三个简并位置使用相同的核苷酸。
