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:8758937, PubMed:8942982, PubMed:9045704). The TFIID complex structure can be divided into 3 modules TFIID-A, TFIID-B, and TFIID-C (PubMed:33795473). TAF5 is involved in two modules of TFIID, in TFIID-A together with TAF3 and TBP, and in TFIID-B with TAF8 (PubMed:33795473). Involved in contacts between TFIID and TFIIF in the PIC (PubMed:33795473). Homodimer (PubMed:17227857). 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:10373431, PubMed:33795473). The TFIID complex structure can be divided into 3 modules TFIID-A, TFIID-B, and TFIID-C (PubMed:33795473). TAF5 forms the TFIID-A module together with TAF3 and TBP, and in TFIID-B with TAF8 (PubMed:33795473). Component of the TFTC-HAT complex, at least composed of TAF5L, TAF6L, TADA3L, SUPT3H/SPT3, TAF2, TAF4, TAF5, GCN5L2/GCN5, TAF10 and TRRAP (PubMed:10373431, PubMed:12601814, PubMed:17227857). TBP is not part of the TFTC-HAT complex (PubMed:10373431, PubMed:12601814). Interacts strongly with the histone H4-related TAF6 and the histone H3-related TAF9, as well as a stable complex comprised of both TAF6 and TAF9 (PubMed:9045704). Apparently weaker interactions with TBP, TAF1, TAF11, and TAF12, but not TAF7, also have been observed (PubMed:8758937, PubMed:9045704). (Microbial infection) Interacts with SV40 Large T antigen. Distinct domains of TAF5/TAFII100 are required for functional interaction with transcription factor TFIIFB (RAP30) and incorporation into the TFIID complex. Belongs to the WD repeat TAF5 family.