TRANSCRIPTION initiation factor TFIID is a multisubunit complex contai
ning a TATA-box-binding factor (TFIIDtau/TBP) and associated polypepti
de factors (TAFs) with sizes ranging from M(r) approximately 20,000 to
>200,000 (refs 1-7). As a result of direct promoter interactions8,9,
TFIID nucleates the assembly of RNA polymerase II and other initiation
factors into a functional preinitiation complex10. Although the nativ
e TFIID complex mediates both basal and activator-dependent transcript
ion in reconstituted systems, TBP itself is competent for only basal t
ranscription. Thus, TAFs are essential cofactors for regulated transcr
iption. The complementary DNAs encoding the p230 (M(r) 230,000), p110
and p85 subunits of TFIID have recently been cloned11-18. Here we repo
rt the molecular cloning and characterization of the p62, p42, p28 and
p22 subunits. These participate in a network of heterogeneous protein
-protein interactions within TFIID. Sequence similarities between p62/
p42 and the histones H4/H3, respectively, suggest that these subunits
have a functional relationship with chromatin.