The TFIID basal transcription factor complex plays a major role in the initiation of RNA polymerase II (Pol II)-dependent transcription (PubMed:33795473). TFIID recognizes and binds promoters with or without a TATA box via its subunit TBP, a TATA-box-binding protein, and promotes assembly of the pre-initiation complex (PIC) (PubMed:33795473). The TFIID complex consists of TBP and TBP-associated factors (TAFs), including TAF1, TAF2, TAF3, TAF4, TAF5, TAF6, TAF7, TAF8, TAF9, TAF10, TAF11, TAF12 and TAF13 (PubMed:33795473, PubMed:10594036, PubMed:8942982). TAF4 may maintain an association between the TFIID and TFIIA complexes, while bound to the promoter, together with TBP, during PIC assembly (PubMed:33795473). Potentiates transcriptional activation by the AF-2S of the retinoic acid, vitamin D3 and thyroid hormone (PubMed:9192867). Component of the TFIID basal transcription factor complex, composed of TATA-box-binding protein TBP, and a number of TBP-associated factors (TAFs), including TAF1, TAF2, TAF3, TAF4, TAF5, TAF6, TAF7, TAF8, TAF9, TAF10, TAF11, TAF12 and TAF13 (PubMed:33795473, PubMed:10594036). Component of the TFTC-HAT complex, at least composed of TAF5L, TAF6L, TADA3L, SUPT3H, TAF2, TAF4, TAF5, GCN5L2/GCN5, TAF10, TAF12 and TRRAP (PubMed:10373431, PubMed:12601814). Component of some MLL1/MLL complex, at least composed of the core components KMT2A/MLL1, ASH2L, HCFC1/HCF1, WDR5 and RBBP5, as well as the facultative components BAP18, CHD8, E2F6, HSP70, INO80C, KANSL1, LAS1L, MAX, MCRS1, MGA, MYST1/MOF, PELP1, PHF20, PRP31, RING2, RUVB1/TIP49A, RUVB2/TIP49B, SENP3, TAF1, TAF4, TAF6, TAF7, TAF9 and TEX10 (PubMed:15960975). Interacts with ATF7; the interaction inhibits ATF7-mediated tranactivation (PubMed:15735663). (Microbial infection) Interacts with SV40 Large T antigen. Belongs to the TAF4 family.