Mechanism of TATA-binding protein recruitment to a TATA-less class III promoter

The TATA-binding protein (TBP) is required for transcription by RNA polymerase III (pol III), even though many pol III templates, such as the adenovirus VA1 gene, lack a consensus TATA box. We show that TBP alone does not form a stable, productive interaction with VA1 DNA. However, it can be incorporated into an initiation complex if the other class III basal factors, TFIIIB and TFIIIC, are also present. TFIIIB can associate with the evolutionarily conserved C-terminal domain of TBP in the absence of DNA or TFIIIC, suggesting that TFIIIB exists in solution as a complex with TBP. The stable association of TBP with an essential component of the pol III transcription apparatus may account for the ability of TATA-less class III genes to recruit TBP.