Envelope sequences of two new United States HIV-1 isolates.

One of the striking molecular aspects of the human T-cell lymphotropic virus type III (HTLV-III) (now called HIV-1) is an unusually large variability in the env genes of different isolates. These differences are clustered primarily within the coding sequences for the large envelope protein and are interspersed among regions within the env gene of relative constancy. Differences among the envelopes of isolates from Africa are so far greater than those among U.S. isolates, but few U.S. isolates have been characterized to date. We report the sequence of the env gene of two U.S. isolates [HTLV-III(MN) and (SC)] and compare them with previously characterized isolates. These two isolates differ substantially from all previously described isolates, especially in the region coding for the large envelope proteins. The env genes of the two new HIV-1 isolates contain conserved and hypervariable regions similar to what has been reported for other isolates, helping to further define those regions. A comparison of the envelope sequences of all the U.S. isolates shows that the similarity between any two ranges from 81 to 85% [except for LAV(BRU) and HTLV-III(BH10) which are 97% similar]. Similar analyses of the African (Zairean) isolates give significantly lower values [71 to 78%, except for 88% between LAV(ELI) and Z6]. This suggests that the African isolates diverged earlier than the U.S. isolates or that transmission of the virus has been more rapid in Africa. Two previous presumptive Haitian isolates are similar to each other and to the U.S. isolates to the same degree as are other U.S. isolates, but differ more markedly from the African isolates suggesting a common lineage of Haitian and U.S. HIV-1 isolates.