p300 and p300/cAMP-responsive element-binding protein associated factor interact with human T-cell lymphotropic virus type-1 Tax in a multi-histone acetyltransferase/activator-enhancer complex

The human T-cell lymphotropic virus, type (HTLV)-1 trans-activator, Tax, co ordinates with cAMP-responsive element-binding protein (CREB) and the trans criptional co-activators p300/CBP on three 21-base pair repeat elements in the proviral long terminal repeat (LTR) to promote viral mRNA transcription . Recruitment of p300/CBP to the activator-enhancer complex, however, is in sufficient to support Tax-dependent LTR trans-activation. Here, we report t hat the p300/CBP-associated factor (P/CAF) is a critical and integral compo nent of the functional HTLV-1 activator-enhancer complex. The HTLV-1 Tax pr otein directly binds P/CAF in vitro and co-immunoprecipitates with this co- activator in vivo. The Tax mutants (K88A and V89A) defective for p300/CBP-b inding and LTR trans-activation, retained their abilities to interact with P/CAF. The M47 mutant (L319R, L320S) protein, which has previously been sho wn to interact with p300/CBP, by contrast, failed to form complexes with P/ CAF and is impaired in LTR trans-activation. Furthermore, LTR trans-activat ion by Tax is competitively inhibited by the adenoviral E1A 12S gene produc t, which displaces P/CAF from p300/CBP and inhibits the histone acetyltrans ferase activities of both P/CAF and p300/CBP. This inhibition is partially reversed by exogenously added P/CAF. These results imply that simultaneous recruitment of two distinct coactivators (p300/CBP and P/CAF) by Tax is ess ential for the assembly of a trans-activation competent, nucleoprotein comp lex.