The simian virus 40 (SV40) early gene product large T antigen promiscu
ously activates simple promoters containing a TATA box or initiator el
ement and at least one upstream transcription factor-binding site. Pre
vious studies have suggested that promoter activation requires that la
rge T antigen interacts with both the basal transcription complex and
the upstream-bound factor. This mechanism of activation is similar to
that proposed for TBP-associated factors (TAFs). We report genetic and
biochemical evidence suggesting that large T antigen performs a TAF-l
ike function. In the ts13 cell line, large T antigen can rescue the te
mperature-sensitive (ts) defect in TAF(II)250. In contrast, neither El
a, small t antigen, nor mutants of large T antigen defective in transc
riptional activation were able to rescue the ts defect. These data sug
gest that transcriptional activation by large T antigen is attributabl
e, at least in part, to an ability to augment or replace a function of
TAF,,250. In addition, we show that large T antigen interacts in vitr
o with the Drosophila TAFs (dTAFs) dTAF(II)150, dTAF(II)110, and dTAF(
II)40, as well as TBP. The relevance of these in vitro results was est
ablished in coimmunoprecipitation experiments using extracts of SV40-i
nfected alpha 3 cells that express an epitope-tagged TBP. Large T anti
gen was coimmunoprecipitated by antibodies to epitope-tagged TBP, endo
genous TBP, hTAF(II)100, hTAF(II)130, and hTAF(II)250, under condition
s where holo-TFIID would be precipitated. In addition, large T antigen
copurified and coimmunoprecipitated with phosphocellulose- purified T
FIID from SV40-infected alpha 3 cells. Large T antigen also coprecipit
ated with anti-TBP antibody from extracts of ts13 cells expressing wil
d-type large T antigen under conditions where the ts defect in TAF(II)
250 was rescued. In contrast, a trans-activation mutant of large T ant
igen, which was unable to rescue the ts defect, failed to coprecipitat
e. We conclude from these data that transcriptional activation of many
promoters by large T antigen results from its performing a TAF-like f
unction in a complex with TFIID.