Constrained evolution with respect to gene overlap of hepatitis B virus
Constrained evolution with respect to gene overlap of hepatitis B virus
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DOI：
10.1007/pl00000061
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发表时间：
1997-01-01
影响因子：
3.9
通讯作者：
Gojobori, T
中科院分区：
文献类型：
--
作者：
Mizokami, M;Orito, E;Gojobori, T
为了阐明肝炎病毒家族的进化，我们采用非加权配对分组和邻居连接方法构建了27株乙型肝炎病毒（HBV）的分子系统发育树。利用P、C、S、X和preS 5个基因区构建系统发育树。利用所获得的系统发育树，我们将这些菌株分为5大类群，这些类群之间的亲缘关系非常密切。我们的分类强化了我们以前的观点，即遗传分类并不总是与由血清学亚型确定的传统分类兼容。此外，我们还分析了HBV进化过程中氨基酸改变（非同义）和沉默（同义）取代的制约因素，因为三分之二的开放阅读框（ORF） P包含交替重叠的ORF。在我们对HBV这个有趣的基因结构的独特分析中，在P和C基因的非重叠部分观察到最常见的同义替换。另一方面，S基因每个核苷酸位点的同义替换数量很低，表现出强烈的进化约束。由于P基因在不同的框架中与S基因重叠，S基因的同义替换率低可以用重叠基因区域施加的进化限制来解释。换句话说，S基因的同义替换会导致不同框架中重叠区域的氨基酸发生变化。因此，HBV的进化受到重叠基因的进化限制。我们建议将这种病毒进化模式称为“约束进化”。“HBV的进化代表了一种典型的受限进化。
With the aim of elucidating the evolution of a hepadnavirus family, we constructed molecular phylogenetic trees for 27 strains of hepatitis B virus (HBV) using both the unweighted pair-grouping and neighbor-joining methods. All five gene regions, P, C, S, X, and preS, were used to construct the phylogenetic trees. Using the phylogenetic trees obtained, we classified these strains into five major groups in which the strains were closely related to each other. Our classification reinforced our previous view that genetic classification is not always compatible with conventional classification determined by serological subtypes. Moreover, constraints on the evolutionary process of HBV were analyzed for amino-acid-altering (nonsynonymous) and silent (synonymous) substitutions, because two-thirds of the open reading frame (ORF), P, contains alternating overlapping ORFs. In our unique analysis of this interesting gene structure of HBV, the most frequent synonymous substitutions were observed in the nonoverlapped parts of the P and C genes. On the other hand, the number of synonymous substitutions per nucleotide site for the S gene was quite low and appeared a strongly constrained evolution. Because the P gene overlaps the S gene in a different frame, the low rate of synonymous substitution for the S gene can be explained by the evolutionary constraints which are imposed on the overlapping gene region. In other words, synonymous substitutions in the S gene can cause amino acid changes in its overlapping region in a different frame. Thus, the evolution of HBV is constrained evolutionarily by the overlapping genes. We propose calling this mode of viral evolution ''constrained evolution.'' The evolution of HBV represents a typical constrained evolution.