A POINT MUTATION IN THE HIV-1 TAT RESPONSIVE ELEMENT IS ASSOCIATED WITH POSTINTEGRATION LATENCY

Study of the mechanism of HIV-1 postintegration latency in the ACH2 ce ll line demonstrates that these cells failed to Increase HIV-1 product ion following treatment with exogenous Tat, Reasoning that the defect in ACH2 cells involves the Tat response, we analyzed the sequence of t at cDNA and Tat responsive element (TAR) from the virus integrated in ACH2. Tat cDNA sequence is closely related to that of HIVLAI, and the encoded protein is fully functional in terms of long terminal repeat ( LTR) transactivation, Cloning of a region corresponding to the 5'-LTR from ACH2, however, identified a point mutation (C-37-->T) in TAR. Thi s mutation impaired Tat responsiveness of the LTR in transient transfe ction assays, and the measured defect was complemented in cells that h ad been treated with tetradecanoyl phorbol acetate or tumor necrosis f actor type alpha (TNF-alpha). A compensatory mutation in TAR (G(28) -- > A), designed to reestablish base pairing in the TAR hairpin, restore d wild-type Tat responsiveness. When the (C-37 --> T) mutation was int roduced in an infectious clone of HIV-1, no viral production was measu red in the absence of TNF-alpha, whereas full complementation was obse rved when the infection was conducted in the presence of TNF-alpha or when a compensatory mutation (G(28) --> A) was introduced into TAR, Th ese experiments identify a novel mutation associated with HIV-1 latenc y and suggest that alterations in the Tat-TAR axis can be a crucial de terminant of the latent phenotype in infected individuals.