SPECIFIC INTERACTIONS AND POTENTIAL FUNCTIONS OF HUMAN TAF(II)100

Human transcription initiation factor TFIID contains the TATA-binding protein (TBP) and several TBP-associated factors (TAFs), To investigat e the structural organization and function of TFIID, we have cloned an d expressed a cDNA encoding the third largest human TFIID subunit, hTA F(II)100, Immunoprecipitation studies demonstrate that hTAF(II)100 is an integral subunit that is associated with all transcriptionally-comp etent forms of TFIID, They further suggest that at least part of the N -terminal region lies on the surface of TFIID, while a C-terminal regi on containing conserved WD-40 repeats appears inaccessible, Both in vi vo and in vitro assays indicate that hTAF,100 interacts strongly with the histone H4-related hTAF(II)80 and the histone H3-related hTAF(II)3 1, as well as a stable complex comprised of both hTAF(II)80 and hTAF(I I)31, Apparently weaker interactions of hTAF(II)100 with TBP, hTAF(II) 250, hTAF(II)28, and hTAF(II)20, but not hTAF(II)55, also have been ob served. These results suggest a role for hTAF,100 in stabilizing inter actions of TAFs, especially the histone-like TAFs, in TFIID, In additi on, functional studies show that anti-hTAF(II)100 antibodies selective ly inhibit basal transcription from a TATA-less initiator-containing p romoter, relative to a TATA containing promoter, suggesting a possible core promoter-specific function for hTAF(II)100.