Characterization of HIV type 1 tat sequences associated with perinatal transmission

Human immunodeficiency virus type 1 (HIV-1) tat exon I sequences were analy zed 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 o f heterogeneity was observed in tat sequences within mothers, within infant s, and between epidemiologically linked mother-infant pairs, However, the d istances of tat sequences between epidemiologically unlinked individuals we re 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 con stitute domains for activation and RNA binding, were highly conserved in mo st of the sequences. Phylogenetic analysis of 154 mother-infant tat sequenc es showed that they formed distinct clusters for each mother-infant pair an d grouped with subtype B sequence. These findings suggest that an intact an d functional tat gene is conserved in HIV-1 mother-infant isolates that are involved in perinatal transmission.