Characterization of HIV type 1 tat sequences associated with perinatal transmission

Human immunodeficiency virus type 1 (HIV-1) tat exon I sequences were analyzed from six mother-infant pairs after perinatal transmission. The tat open reading frame was maintained in 140 of the 154 clones analyzed, with a 90.9% frequency of intact tat open reading frames. In addition, a low degree of heterogeneity was observed in tat sequences within mothers, within infants, and between epidemiologically linked mother-infant pairs. However, the distances of tat sequences between epidemiologically unlinked individuals were greater than in epidemiologically linked mother-infant pairs. The infant sequences showed amino acid sequence patterns similar to those present in their respective mothers. The functional domains required for Tat function, including amino-terminal, cysteine-rich, core and basic regions, which constitute domains for activation and RNA binding, were highly conserved in most of the sequences. Phylogenetic analysis of 154 mother-infant tat sequences showed that they formed distinct clusters for each mother-infant pair and grouped with subtype B sequence. These findings suggest that an intact and functional tat gene is conserved in HIV-1 mother-infant isolates that are involved in perinatal transmission.