HUMAN TAF(II)28 INTERACTS WITH THE HUMAN T-CELL LEUKEMIA-VIRUS TYPE-ITAX TRANSACTIVATOR AND PROMOTES ITS TRANSCRIPTIONAL ACTIVITY

The Tax protein encoded by human T cell leukemia virus type I transact ivates the viral promoter by forming a complex with several cellular f actors bound to three repeats of a specific upstream regulatory sequen ce. We have shown that transactivation by Tax was correlated with its ability to interact with the C-terminal moiety of the TATA box-binding protein (TBP). In the present study, the ability of Tax to interact w ith several human TBP-associated factors (TAF(II)s) was analyzed. We s how that Tax interacts selectively with hTAF(II)28 in transfected HeLa cells. A direct interaction between Tax and hTAF(II)28 was also obser ved in vitro with purified proteins. In transient expression studies w e show that overexpression of hTAF(II)28 significantly increased trans activation by Tax, both in the absence and in the presence of overexpr essed TBP. The ability of hTAF(II)28 to potentiate transactivation cor related with the ability of Tax to interact with hTAF(II)28 and also w ith the ability of hTAF(II)28 to interact with TBP. Coexpression of TB P and hTAF(II)28 resulted in an additive increase in transactivation b y Tax. From these observations we propose that transcriptional activat ion by Tax involves multiple interactions with TFIID via its TBP and h TAF(II)28 subunits.