Khrustalev Vladislav Victorovich, Barkovsky Eugene Victorovich
Department of General Chemistry, Belarussian State Medical University, Minsk, Belarus.
IUBMB Life. 2008 Jul;60(7):456-60. doi: 10.1002/iub.55.
The purpose of our work was to analyze the case of the strong mutational GC-pressure influence on the ratio between nonsynonymous (DN) and synonymous (DS) distances (DN/DS ratio). We have used as the material the genes coding for ICP0 from five completely sequenced genomes of simplexviruses. DN/DS ratio, total GC-content (G + C), and GC-content in first, second, and third codon positions (1GC, 2GC, and 3GC, respectively) have been calculated separately for exon 2, nonconserved part of exon 3, and conserved part of exon 3 from ICP0 genes. Results showed that DN is more than DS only in the conserved part of exon 3 of ICP0 genes from cercopithecine herpesvirus 2 and cercopithecine herpesvirus 16. However, the cause of this result (DN/DS = 2.54) is the GC-pressure acting on the coding districts with 3GC = 99% rather than the biological process called positive selection. Only in these two viruses, because of the strong GC-pressure, 3GC has reached 99% in the conserved part of ICP0 exon 3, and so nucleotide substitutions that increase the GC-content practically cannot occur in third codon positions, where most substitutions are synonymous. In this case, GC-pressure has a substrate for nucleotide substitutions only in first and second codon positions, where most substitutions are nonsynonymous.
我们工作的目的是分析强突变GC压力对非同义（DN）与同义（DS）距离之比（DN/DS比）的影响情况。我们使用了来自五种完全测序的单纯疱疹病毒基因组中编码ICP0的基因作为材料。分别计算了ICP0基因外显子2、外显子3的非保守部分和外显子3的保守部分的DN/DS比、总GC含量（G + C）以及第一、第二和第三密码子位置的GC含量（分别为1GC、2GC和3GC）。结果表明，只有在猕猴疱疹病毒2和猕猴疱疹病毒16的ICP0基因外显子3的保守部分中，DN大于DS。然而，这一结果（DN/DS = 2.54）的原因是GC压力作用于3GC = 99%的编码区，而非所谓的正向选择这一生物学过程。仅在这两种病毒中，由于强大的GC压力，ICP0外显子3的保守部分中3GC达到了99%，因此增加GC含量的核苷酸替换实际上无法在第三密码子位置发生，而在该位置大多数替换是同义的。在这种情况下，GC压力仅在第一和第二密码子位置有核苷酸替换的底物，而在这些位置大多数替换是非同义的。
