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 and 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. May be involved in regulating folliculogenesis. 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) (PubMed:15601843). Heterodimerizes with TAF12/TFII20 via the C-terminal H2A-like histone-fold domain (PubMed:15601843). This heterodimer forms a histone-like octamer with the TAF6/TAFII70-TAF9/TAFII31 heterodimer (PubMed:15601843). Interacts with P65/RELA homodimers and P65/RELA-REL heterodimers (PubMed:10849440). Interaction with POU2AF1, via its C-terminal activation domain, is required for octamer-dependent transcription (PubMed:10828057). Interacts with ZNF628 (By similarity). Export into the cytoplasm is mediated by a CRM1-independent nuclear export pathway and not by phosphorylation. Preferentially expressed in ovarian granulosa cells (at protein level). Highly expressed in B-cells. Under stimulation by forskolin, Isoform 1 is phosphorylated by protein kinase A (PKA). The disease is caused by variants affecting the gene represented in this entry. May be due to exon inclusion. Unphosphorylated form. Belongs to the TAF4 family.