Department of Mathematical Sciences, Tezpur University, Assam, India.
Genes Cells. 2010 Jun;15(7):773-82. doi: 10.1111/j.1365-2443.2010.01417.x. Epub 2010 Jun 7.
According to the selection-mutation-drift theory of molecular evolution, mutation predominates in determining codon usage bias (CUB) in weakly expressed genes (WEG) whereas selection predominates in determining CUB in highly expressed genes (HEG). Strand-specific mutational bias causes compositional asymmetry of the nucleotides between leading and lagging strands (LaS) in bacterial chromosomes. Keeping in view the aforementioned points, CUB between the strands were compared in Escherichia coli chromosome. In comparison with HEG, codon usage of WEG was observed to be more biased toward strands: G ending codons were significantly more in leading strands than in LaS and the reverse was true for the C ending codons. In case of WEG, the GC(3) skews were found to be significantly different between the strands. This suggests that strand-specific mutational bias influences codon usage of WEG to a greater extent than that of HEG. The differential effect of strand-specific mutational bias in E. coli might be attributed to stronger purifying selection in the HEG than the WEG. The observation here in E. coli supports the SMD theory of molecular evolution.
根据分子进化的选择-突变-漂变理论，在弱表达基因（WEG）中，突变在决定密码子使用偏好（CUB）方面占主导地位，而在高表达基因（HEG）中，选择在决定 CUB 方面占主导地位。链特异性突变偏倚导致细菌染色体中前导链和滞后链（LaS）之间核苷酸的组成不对称。鉴于上述观点，比较了大肠杆菌染色体中两条链之间的 CUB。与 HEG 相比，观察到 WEG 的密码子使用偏向于链：G 结尾密码子在前导链中明显多于 LaS，而 C 结尾密码子则相反。在 WEG 的情况下，发现两条链之间的 GC（3）倾斜有显著差异。这表明，与 HEG 相比，链特异性突变偏倚对 WEG 的密码子使用有更大的影响。在大肠杆菌中，链特异性突变偏倚的差异效应可能归因于 HEG 中的净化选择强于 WEG。在大肠杆菌中的观察结果支持分子进化的 SMD 理论。
