title: [Study on the evolutionary pressure on the env gene of the human immunodeficiency virus type 1 CRF01-AE strains circulating in China].
abstract: OBJECTIVE
  To identify variations in the env gene of human immunodeficiency virus type 1 (HIV-1) subtype CRF01-AE strains circulating in China and to elucidate the potential relationship between genetic variation and evolutionary pressure.
  
  
  METHODS
  Fragments of the HIV-1 env gene were amplified by nested-polymerase chain reaction (n-PCR) from the whole blood of HIV-1 infected individuals from four provinces in Southeast China (Guangdong, Hunan, Jiangsu and Jiangxi). The PCR products were then directly sequenced by ABI 377 DNA sequencers. The sequences covering the env V3-V4 region of 34 HIV-1 subtype CRF01-AE strains were selected to analyse phylogenetic trees and amino acid mutations. The accumulation of synonymous (Ks) and antonymous (Ka) substitutions as well as Ks/Ka ratios were calculated using DIVERGE.
  
  
  RESULTS
  Phylogenetic trees showed that the 34 HIV-1 subtype CRF01-AE strains from China clustered with the Chinese AE reference strain (AE.97CNGX2F), as well as with the reference strains from Thailand (AE.CM240 and AE.93TH253). The amino acid sequences of the env V4 and C3 regions in the samples were highly variable, compared with those of V3 and V3-downstream regions. The V3 loop central motif in the majority (87.5%) of the strains was GPGQ. The majority of strains did not contain positively charged amino acids at positions 306 and 320 in V3 loop. The N-linked glycosylation sites in the V3-V4 region and flanking regions in these strains were relatively conserved. Analysis of the entire region showed that the mean Ks values were significantly higher than that of the Ka values (P < 0.001), with the Ks/Ka significantly higher than 1.0 (P < 0.001). In contrast, the Ks/Ka ratio in the V4 region was significantly lower than 1.0 (P < 0.01).
  
  
  CONCLUSIONS
  Our study indicated that the majority of HIV-1 subtype CRF01-AE strains circulating in China were highly homogeneous. The amino acid sequences of the V4 and C3 regions were significantly more variable than those of the V3 loop. Our analysis also suggested that the phenotype of nearly all strains was likely to be non-syncytium inducing (NSI). Finally, the variation found in the V3-V4 sequence was significantly influenced by functional constraints as opposed to positive selective pressure, while the variability of the lone V4 region was strongly related to positive selective pressure.
authors.affiliation: National Center for Sexually Transmitted Disease and Acquired Immune Deficiency Syndrome Prevention and Control, Chinese Center for Disease Prevention and Control, Beijing 100050, China.
authors.forename: Hao
authors.initials: H
authors.lastname: Liang
authors.forename: Hui
authors.initials: H
authors.lastname: Xing
authors.forename: Min
authors.initials: M
authors.lastname: Wei
authors.forename: Zhao
authors.initials: Z
authors.lastname: Chen
authors.forename: Qi
authors.initials: Q
authors.lastname: Guan
authors.forename: Hai-long
authors.initials: HL
authors.lastname: Huang
authors.forename: Yu
authors.initials: Y
authors.lastname: Quan
authors.forename: Jian-ping
authors.initials: JP
authors.lastname: Chen
authors.forename: Kun-xue
authors.initials: KX
authors.lastname: Hong
authors.forename: Lü-yuan
authors.initials: LY
authors.lastname: Shi
authors.forename: Yi-ming
authors.initials: YM
authors.lastname: Shao
mesh_terms: D000328:Adult; D000595:Amino Acid Sequence; D002681:China; D019143:Evolution, Molecular; D005260:Female; D015752:Genes, env / Q000235:genetics*; D014644:Genetic Variation; D015497:HIV-1 / Q000235:genetics*; D006801:Humans; D008297:Male; D008875:Middle Aged; D008969:Molecular Sequence Data; D010802:Phylogeny; D016133:Polymerase Chain Reaction; D017386:Sequence Homology, Amino Acid