Essential for RNA polymerase III to make a number of small nuclear and cytoplasmic RNAs, including 5S RNA, tRNA, and adenovirus- associated (VA) RNA of both cellular and viral origin (PubMed:10523658). Has histone acetyltransferase activity (HAT) with unique specificity for free and nucleosomal H3 (PubMed:10523658). May cooperate with GTF3C5 in facilitating the recruitment of TFIIIB and RNA polymerase through direct interactions with BRF1, POLR3C and POLR3F (PubMed:10523658). May be localized close to the A box (PubMed:10523658). . This is the function of ENSG00000125484 (GTF3C4, general transcription factor IIIC subunit 4).