Sequence analysis of the V3 loop regions of the env genes of Ugandan human immunodeficiency proviruses.

Ugandan strains of human immunodeficiency virus type 1 (HIV-1) were isolated by cocultivation of peripheral blood lymphocytes from infected individuals with cord blood lymphocytes. Sequences from the V3 region of the env gene were amplified by the polymerase chain reaction (PCR) from chromosomal DNA obtained from low passage virus cultures. The PCR products from 13 Ugandan isolates were cloned into a phagemid vector and sequenced. Many isolates contained divergent V3 loop sequences and adjacent regions: diversity was associated with codon deletions or duplications and with nucleotide substitutions, especially G----A transitions. Proviruses from some of the cultures showed extensive diversity within the V3 loop sequences but others were more homogeneous. The V3 loop apices were conserved in 6 of the Ugandan proviruses and these were very similar to the equivalent regions of several Zairean proviruses. The V3 loop apices of African isolates of HIV-1 are divergent from those of North American isolates. The possible biological consequences of this divergence are discussed.