TRANSCRIPTION initiation factor TFIID is a multisubunit complex containing a TATA-box-binding factor (TFIIDtau/TBP) and associated polypeptide 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 native TFIID complex mediates both basal and activator-dependent transcription in reconstituted systems, TBP itself is competent for only basal transcription. Thus, TAFs are essential cofactors for regulated transcription. The complementary DNAs encoding the p230 (M(r) 230,000), p110 and p85 subunits of TFIID have recently been cloned11-18. Here we report 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.