Shields D C, Sharp P M, Higgins D G, Wright F
Department of Genetics, Trinity College, Dublin, Ireland.
Mol Biol Evol. 1988 Nov;5(6):704-16. doi: 10.1093/oxfordjournals.molbev.a040525.
The patterns of synonymous codon usage in 91 Drosophila melanogaster genes have been examined. Codon usage varies strikingly among genes. This variation is associated with differences in G+C content at silent sites, but (unlike the situation in mammalian genes) these differences are not correlated with variation in intron base composition and so are not easily explicable in terms of mutational biases. Instead, those genes with high G+C content at silent sites, resulting from a strong "preference" for a particular subset of the codons that are mostly C-ending, appear to be the more highly expressed genes. This suggests that G+C content is reduced in sequences where selective constraints are weaker, as indeed seen in a pseudogene. These and other data discussed are consistent with the effects of translational selection among synonymous codons, as seen in unicellular organisms. The existence of selective constraints on silent substitutions, which may vary in strength among genes, has implications for the use of silent molecular clocks.
对91个黑腹果蝇基因中的同义密码子使用模式进行了研究。密码子使用在基因间差异显著。这种差异与沉默位点的G+C含量差异相关，但（与哺乳动物基因的情况不同）这些差异与内含子碱基组成的变化不相关，因此难以用突变偏好来解释。相反，那些在沉默位点具有高G+C含量的基因，是由于对大多数以C结尾的特定密码子子集有强烈“偏好”，这些基因似乎是表达水平较高的基因。这表明在选择性限制较弱的序列中G+C含量会降低，正如在假基因中所观察到的那样。所讨论的这些及其他数据与单细胞生物中同义密码子间的翻译选择效应一致。对沉默替换存在的选择性限制，其强度在基因间可能有所不同，这对沉默分子钟的使用具有启示意义。
