Eyre-Walker A, Bulmer M
Department of Biological Sciences, Rutgers University, Piscataway, New Jersey 08855-1059, USA.
Genetics. 1995 Aug;140(4):1407-12. doi: 10.1093/genetics/140.4.1407.
It has been shown previously that the synonymous substitution rate between Escherichia coli and Salmonella typhimurium is lower in highly than in weakly expressed genes, and it has been suggested that this is due to stronger selection for translational efficiency in highly expressed genes as reflected in their greater codon usage bias. This hypothesis is tested here by comparing the substitution rate in codon families with different patterns of synonymous codon use. It is shown that the decline in the substitution rate across expression levels is as great for codon families that do not appear to be subject to selection for translational efficiency as for those that are. This implies that selection on translational efficiency is not responsible for the decline in the substitution rate across genes. It is argued that the most likely explanation for this decline is a decrease in the mutation rate. It is also shown that a simple evolutionary model in which synonymous codon use is determined by a balance between mutation, selection for an optimal codon, and genetic drift predicts that selection should have little effect on the substitution rate in the present case.
先前的研究表明，大肠杆菌和鼠伤寒沙门氏菌之间的同义替换率在高表达基因中低于低表达基因，并且有人提出，这是由于高表达基因对翻译效率的选择更强，这体现在它们更大的密码子使用偏好上。本文通过比较具有不同同义密码子使用模式的密码子家族中的替换率来检验这一假设。结果表明，对于那些似乎不受翻译效率选择影响的密码子家族，以及那些受影响的密码子家族，其替换率在不同表达水平上的下降幅度是一样的。这意味着，对翻译效率的选择并不是基因间替换率下降的原因。有人认为，这种下降最可能的解释是突变率的降低。研究还表明，一个简单的进化模型，即同义密码子的使用由突变、对最优密码子的选择和遗传漂变之间的平衡所决定，预测在当前情况下选择对替换率的影响应该很小。
