The TFIID basal transcription factor complex plays a major role in the initiation of RNA polymerase II (Pol II)-dependent transcription (By similarity). TFIID recognizes and binds promoters via its subunit tbp-1, a TATA-box-binding protein, and promotes assembly of the pre-initiation complex (PIC) (By similarity). The TFIID complex consists of tbp-1 and TBP-associated factors (TAFs), including taf-4 (By similarity). Essential for early embryonic development, probably acting via activating transcription initiation by RNA polymerase II, as part of the TFIID complex (PubMed:18854162, PubMed:11566890). In early embryos, but not oocytes, remains, presumably inactive, in the cytoplasm as a result of binding to oma-1 (PubMed:18854162). Upon degradation of oma-1, taf-4 is released and bound by taf-12, and the taf-4/12 heterodimer translocates to the nucleus and transcriptional repression is relieved (PubMed:18854162). Involved in lifespan extension in a manner dependent upon mitochondrial function (PubMed:24107417). Plays a role in modulating polyribosome formation (PubMed:30198021). Component of the TFIID basal transcription factor complex, composed of TATA-box-binding protein tbp-1, and a number of TBP-associated factors (TAFs) (By similarity). Interacts (via histone-fold domain) with oma-1 (via histone-fold domain) (PubMed:18854162). May also interact with oma-2 (PubMed:18854162). Interacts (via histone-fold domain) with taf-12 (via the histone-fold domain) (PubMed:18854162). Localization is ubiquitous in one-cell and early two-cell embryos, then enriched in nucleus in all subsequent embryo stages (PubMed:18854162). Localization to the nucleus is prevented by interaction with oma-1 and is sequestered in the cytoplasm, following fertilization, and thus allows for transcriptional suppression in early embryos, but not in oocytes (PubMed:18854162). Localized to the nucleus in a taf-12-dependent manner (PubMed:18854162). Expressed in one-, two- and four-cell embryos and through early morphogenesis (at protein level) (PubMed:11566890, PubMed:18854162). Also expressed in oocytes, and until at least 12-cell stage in embryos (PubMed:18854162). The histone-fold domain mediates hetero-dimer protein-protein interactions. RNAi-mediated knockdown causes arrested development at 90-100 cells and inhibits differentiation (PubMed:11566890). The two E cell daughters (E2 cells), which form the endoderm, divide abnormally early, immediately after the MS2 cells (PubMed:11566890). Phosphorylation of the RNA Pol II large subunit C-terminal domain (CTD) is reduced severely in embryos (PubMed:11566890). Abolishes expression of a range of genes, including let-858, rps-5, hsp16.2, pes-10, cki-2 and sur-5 (PubMed:11566890). RNAi-mediated knockdown in a Rieske iron-sulfur protein isp-1 mutant background abolishes lifespan extension, drastically reduces fertility, and abolishes induction of expression of glutathione S-transferase gst-4 (PubMed:24107417). Knockdown also significantly shortens lifespan in either tpk-1 or clk-1 mutant backgrounds (PubMed:24107417). Causes significant up-regulation of expression of the translation initiation factor eif-1, in a clk-1 mutant background (PubMed:30198021). Belongs to the TAF4 family. Throughout PMID:11566890, the gene name taf-5 is used instead of taf-4, based on an earlier nomenclature; readers should be aware to avoid confusion.