General activator of RNA polymerase which utilizes different TFIIIB complexes at structurally distinct promoters. TFIIIB comprises at least the TATA-binding protein (TBP) and the B-related factor 1 (BRF1/TFIIIB90). Interacts with BDP1 (By similarity). Interacts with MAF1 (By similarity). Belongs to the TFIIB family.