SEQUENCE VARIATION AND PHYLOGENETIC ANALYSIS OF ENVELOPE GLYCOPROTEINOF HEPATITIS-G VIRUS

A transfusion-transmissible agent provisionally designated hepatitis G virus (HGV) was recently identified. In this study, we examined the v ariability of the HGV genome by analysing sequences in the putative en velope region from 72 isolates obtained from diverse geographical sour ces. The 1561 nucleotide sequence of the E1/E2/NS2a region of HGV was determined from 12 isolates, and compared with three published sequenc es. The most variability was observed in 400 nucleotides at the N term inus of E2. We next analysed this 400 nucleotide envelope variable reg ion (EV) from an additional 60 HGV isolates. This sequence varied cons iderably among the 75 isolates, with overall identity ranging from 79. 3% to 99.5% at the nucleotide level, and from 83.5% to 100% at the ami no acid level. However, hypervariable regions were not identified. Phy logenetic analyses indicated that the 75 HGV isolates belong to a sing le genotype. A single-tier distribution of evolutionary distances was observed among the 15 E1/E2/NS2a sequences and the 75 EV sequences. In contrast, 11 isolates of HCV were analysed and showed a three-tiered distribution, representing genotypes, subtypes, and isolates. The 75 i solates of HGV fell into four clusters on the phylogenetic tree. Tight geographical clustering was observed among the HGV isolates from Japa n and Korea.