Cell type-specific subunit of the general transcription factor TFIID that may function as a gene-selective coactivator in certain cells. TFIID is a multimeric protein complex that plays a central role in mediating promoter responses to various activators asond repressors. TAF4B is a transcriptional coactivator of the p65/RELA NF-kappa-B subunit. Involved in the activation of a subset of antiapoptotic genes including TNFAIP3. Through interaction with OCBA/POU2AF1, acts as a coactivator of B-cell-specific transcription. Plays a role in spermiogenesis and oogenesis. TFIID is composed of TATA binding protein (TBP) and a number of TBP-associated factors (TAFs). Heterodimerizes with TAF12/TFII20 via the C-terminal H2A-like histone-fold domain. This heterodimer forms a histone-like octamer with the TAF6/TAFII70-TAF9/TAFII31 heterodimer. Interacts with P65/RELA homodimers and P65/RELA-REL heterodimers. Interaction with POU2AF1, via its C-terminal activation domain, is required for octamer-dependent transcription (By similarity). Interacts with ZNF628 (PubMed:31932482). Export into the cytoplasm is mediated by a CRM1-independent nuclear export pathway and not by phosphorylation. Highly expressed in the testes and ovary, whereas lower levels are detected in most other tissues. Deficient female mice are infertile due to a granulosa cell defect preventing normal follicle formation. Deficient male are fertile when young, but subsequently exhibit an age-dependent progressive loss of germ cells and misregulation of several genes required for normal spermatogenesis. Belongs to the TAF4 family.