The Brf and TATA-binding protein subunits of the RNA polymerase III transcription factor IIIB mediate position-specific integration of the gypsy-likeelement, Ty3

Ty3 integrates into the transcription initiation sites of genes transcribed by RNA polymerase III. It is known that transcription factors (TF) IIIB an d IIIC are important for recruiting Ty3 to its sites of integration upstrea m of tRNA genes, but that RNA polymerase III is not required. In order to i nvestigate the respective roles of TFIIIB and TFIIIC, we have developed an in vitro integration assay in which Ty3 is targeted to the U6 small nuclear RNA gene, SNR6. Because TFIIIB can bind to the TATA box upstream of the U6 gene through contacts mediated by TATA-binding protein (TBP), TFIIIC is di spensable for in vitro transcription. Thus, this system offers an opportuni ty to test the role of TFIIIB independent of a requirement of TFIIIC. We de monstrate that the recombinant Brf and TBP subunits of TFIIIB, which intera ct over the SNR6 TATA box, direct integration at the SNR6 transcription ini tiation site in the absence of detectable TFIIIC or TFIIIB subunit B". Thes e findings suggest that the minimal requirements for pol III transcription and Ty3 integration are very similar.