中国HIV-1型B、C亚型主要流行株外膜蛋白基因V3-V4区序列的变异分析

目的　研究我国人类免疫缺陷病毒 1型 (HIV 1)B、C亚型主要流行株在感染过程中基因变异的特点及其与选择压力的关系。方法　应用巢式聚合酶链反应 (nested PCR)对 2 5 8例HIV 1感染者血样中的HIV 1外膜蛋白 (env)基因进行扩增 ,并使用ABI 377型测序仪对扩增产物测序后 ,选择其中 37份B亚型和 35份C亚型HIV 1毒株env基因包括V3～V4区的序列进行比较分析 ,并计算和分析氨基酸同义替换与非同义替换的比值 (Ks Ka)。结果　B亚型毒株V3～V4区的基因离散率高于C亚型毒株。无论B亚型 ,还是C亚型毒株 ,其V4区基因序列较V3区变异更大。在C亚型毒株中 ,V3区基因序列变异甚至比V3上游区和C3区小。B和C亚型毒株整个V3～V4基因区的Ks Ka比值均 <1,差异有非常显著性 (P <0 0 0 1) ,其中B亚型毒株以V3区的Ks Ka比值最小 ,而C亚型毒株则以V4区的Ks Ka比值最小。结论　B和C亚型毒株env基因的变异主要发生在V4区而不是V3区。C亚型毒株V3区较V3上游区和C3区还要保守 ,是本研究的特殊发现。这两种亚型在我国快速流行中发生的变异是在选择压力下发生的 ,而不是随机进化的结果 ,而且选择压力对这两种亚型毒株V3、V4区的作用程度也不一样。这将为我国艾滋病防治策略的制定和疫苗研究提供科学的依据。

Sequence variation in the env V3-V4 region of HIV type 1 predominant subtype B and C strains circulating in China

Objective To identify genetic variation of HIV 1 predominant subtype B and C strains in China during rapid horizontal transmission and to elucidate the potential relationship between genetic variation and selective pressure Methods After the fragments of HIV 1 env gene were amplified by nested PCR from the whole blood of 258 HIV 1 infected individuals, PCR products were directly sequenced using ABI 377 DNA sequencer The sequences covering env V3 V4 region of 72 HIV 1 subtype B(n=37) and C(n=35) strains were selected for phylogenetic analysis In addition, the ratios of synonymous (Ks) substitutions per nonsynonymous (Ka) substitutions were calculated using DIVERGE Results The genetic distances of the V3 V4 region of subtype B strains were higher than that of subtype C strains Furthermore, sequence analysis revealed that the V4 region was more variable than the V3 region for both subtype B and C strains What's more, the V3 loop was less variable compared with the V3 upstream region and C3 region for subtype C Ks/Ka ratios of the entire aligned sequence of the two subtypes were below 1 0, with the lowest values found in the V3 region of subtype B strain and the V4 region of subtype C strain Conclusion The majority of variation in both subtypes B and C strains occurred in the V4 rather than the V3 region It is important that our study found for the first time the V3 loop was more conservative than the V3 upstream region and C3 region for subtype C Calculations of the Ks/Ka ratios throughout the V3 V4 region demonstrate that significant selective pressures experienced during the rapid horizontal spread of the virus in the Chinese HIV 1 infected population may have directed change in the V3 loop for the subtype B strain and the V4 loop for the subtype C strain These results will contribute to the policy of AIDS prevention and control and the ongoing development of AIDS vaccine