Lobry J R
Laboratoire de Biométrie, Unversité Claude Bernard, Villeurbanne, France.
Mol Biol Evol. 1996 May;13(5):660-5. doi: 10.1093/oxfordjournals.molbev.a025626.
Analyses of the genomes of three prokaryotes, Escherichia coli, Bacillus subtilis, and Haemophilus influenzae, revealed a new type of genomic compartmentalization of base frequencies. There was a departure from intrastrand equifrequency between A and T or between C and G, showing that the substitution patterns of the two strands of DNA were asymmetric. The positions of the boundaries between these compartments were found to coincide with the origin and terminus of chromosome replication, and there were more A-T and C-G deviations in intergenic regions and third codon positions, suggesting that a mutational bias was responsible for this asymmetry. The strand asymmetry was found to be due to a difference in base compositions of transcripts in the leading and lagging strands. This difference is sufficient to affect codon usage, but it is small compared to the effects of gene expressivity and amino-acid composition.
对三种原核生物——大肠杆菌、枯草芽孢杆菌和流感嗜血杆菌的基因组分析，揭示了一种碱基频率的新型基因组分区现象。A与T之间或C与G之间的链内等频率出现了偏离，这表明DNA两条链的替换模式是不对称的。发现这些分区之间边界的位置与染色体复制的起点和终点相吻合，并且在基因间区域和密码子第三位上有更多的A-T和C-G偏差，这表明突变偏好是造成这种不对称的原因。发现链不对称是由于前导链和后随链中转录本碱基组成的差异所致。这种差异足以影响密码子的使用，但与基因表达能力和氨基酸组成的影响相比则较小。
