General transcription factor that functions at the core of the DNA-binding multiprotein factor TFIID (PubMed:2374612, PubMed:2363050, PubMed:2194289, PubMed:9836642, PubMed:27193682). Binding of TFIID to the TATA box is the initial transcriptional step of the pre-initiation complex (PIC), playing a role in the activation of eukaryotic genes transcribed by RNA polymerase II (PubMed:2374612, PubMed:2363050, PubMed:2194289, PubMed:9836642, PubMed:27193682). Component of a BRF2-containing transcription factor complex that regulates transcription mediated by RNA polymerase III (PubMed:26638071). Component of the transcription factor SL1/TIF-IB complex, which is involved in the assembly of the PIC (pre-initiation complex) during RNA polymerase I-dependent transcription (PubMed:15970593). The rate of PIC formation probably is primarily dependent on the rate of association of SL1 with the rDNA promoter. SL1 is involved in stabilization of nucleolar transcription factor 1/UBTF on rDNA.