Zhao Xiangrong, McGirr Kathleen M, Buehring Gertrude C
Graduate Program in Endocrinology, University of California at Berkeley, 3060 Valley Life Science Building, Berkeley, CA 94720-3140, USA.
Genomics. 2007 Apr;89(4):502-11. doi: 10.1016/j.ygeno.2006.12.007. Epub 2007 Jan 18.
Bovine leukemia virus contains a pXBL region encoding the 3' parts of four regulatory proteins (Tax, Rex, G4, R3) in overlapping reading frames. Here we report the pXBL polymorphisms of 30 isolates from four countries. Rates of overall and synonymous substitutions were consistently lower, and nucleotide/amino acid composition bias and codon bias higher, in more-overlapped than in less-overlapped regions. Ratios of nonsynonymous/synonymous substitutions were lowest in the tax gene and its subregions. The 5' parts of the four genes showed selection patterns corresponding to their genomic context outside of the pXBL region. Longer G4 variants due to a natural stop codon mutation had additional triple overlap with reduced sequence variability. These data support the concept that a higher level of overlapping in coding regions correlates with greater evolutionary constraint. Tax, the most conserved among the four regulatory proteins, showed purifying selection consistent with its importance in the viral life cycle.
牛白血病病毒含有一个pXBL区域，该区域在重叠阅读框中编码四种调节蛋白（Tax、Rex、G4、R3）的3'部分。在此，我们报告了来自四个国家的30个分离株的pXBL多态性。与重叠较少的区域相比，重叠较多的区域中总体和同义替换率始终较低，核苷酸/氨基酸组成偏差和密码子偏差较高。非同义/同义替换率在tax基因及其亚区域中最低。这四个基因的5'部分显示出与其在pXBL区域之外的基因组背景相对应的选择模式。由于自然终止密码子突变导致的较长G4变体具有额外的三重重叠，序列变异性降低。这些数据支持了编码区域中更高水平的重叠与更大的进化限制相关的概念。Tax是四种调节蛋白中最保守的，显示出纯化选择，与其在病毒生命周期中的重要性一致。
