Li J S, Tong S P, Wen Y M, Vitvitski L, Zhang Q, Trépo C
Unité de Recherche sur les Hepatites, le SIDA et les Retrovirus Humains, Institut National de la Santé et de la Recherche Médicale 271, Lyon, France.
J Virol. 1993 Sep;67(9):5402-10. doi: 10.1128/JVI.67.9.5402-5410.1993.
The emergence of HBe-minus hepatitis B virus (HBV) mutants, usually through a UAG nonsense mutation at codon 28 of the precore region, helps the virus to survive the anti-HBe immune response of the host. Host and viral factors that predispose to the emergence of such mutants are not well characterized. The fact that the precore region forms a hairpin structure essential for the packaging of viral pregenomic RNA may explain the extremely high prevalence of the UAG mutation at codon 28. It converts a wobble U-G pair in the packaging signal between nucleotide 3 of codon 15 (CCU) and nucleotide 2 of codon 28 (UGG) into a U-A pair. Since genotype A of HBV has a CCC sequence at codon 15, the UAG mutation would, instead, disrupt a C-G pair present in the wild-type virus. This alteration was shown by transfection experiments to greatly compromise the packaging of pregenomic RNA. The implication of this finding was elucidated by molecular epidemiological studies. Genotype A was found to be the most prevalent genotype in the wild-type virus populations in France but was found in only 1 of the 46 isolates of HBe-minus mutants found there. These mutants were contributed chiefly by genotype D, the second most prevalent genotype in France, which is characterized by a CCU sequence at codon 15. The role of the single nucleotide at codon 15 was confirmed by the finding of the single genotype A isolate in which both wild-type and mutant viruses were present. Interestingly, nearly all of the mutants had a codon 15 sequence of CCU instead of the CCC present in the wild-type viruses. Our results suggest that genotype A of HBV rarely circulates as HBe-minus mutants, probably because of a requirement for a simultaneous sequence change at codon 15. These data, together with the virtual absence of genotype A in the Chinese samples examined, may provide some insights into the uneven prevalence of HBe-minus mutants in the world.
乙型肝炎病毒（HBV）前核心区缺失突变体（HBe -）的出现，通常是通过前核心区第28位密码子处的UAG无义突变实现的，这有助于病毒在宿主的抗HBe免疫反应中存活。导致此类突变体出现的宿主和病毒因素尚未得到充分表征。前核心区形成对病毒前基因组RNA包装至关重要的发夹结构这一事实，可能解释了第28位密码子处UAG突变的极高发生率。它将密码子15（CCU）的第3位核苷酸与密码子28（UGG）的第2位核苷酸之间包装信号中的摆动U - G对转换为U - A对。由于HBV A基因型在密码子15处具有CCC序列，因此UAG突变反而会破坏野生型病毒中存在的C - G对。转染实验表明，这种改变会极大地损害前基因组RNA的包装。分子流行病学研究阐明了这一发现的意义。在法国，A基因型是野生型病毒群体中最常见的基因型，但在那里发现的46株HBe - 突变体分离株中仅发现了1株。这些突变体主要由D基因型贡献，D基因型是法国第二常见的基因型，其在密码子15处的特征序列为CCU。在同时存在野生型和突变型病毒的单个A基因型分离株中的发现，证实了密码子15处单个核苷酸的作用。有趣的是，几乎所有突变体在密码子15处的序列都是CCU，而不是野生型病毒中的CCC。我们的结果表明，HBV A基因型很少以前核心区缺失突变体的形式传播，可能是因为需要在密码子15处同时发生序列变化。这些数据，连同在所检测的中国样本中几乎没有A基因型，可能为世界上前核心区缺失突变体的不均衡流行提供一些见解。
