The recruitment of Brf1-TFIIIB to type 1 and 2 promoters has been intensively studied in S. cerevisiae (Joazeiro et al., 1996). The Tfc4 subunit of TFIIIC, which protrudes upstream of the transcription start site (Bartholomew et al., 1990), can interact with the Brf1 subunit of Brf1-TFIIIB (Moir et al., 1997). The Tfc4 subunit, which contains 11 copies of the tetratricopeptide repeat (TPR), appears to undergo conformational changes during binding that promote association with ScBrf1 and accommodate variable placements of TFIIIB (Moir et al., 1997). As shown in the figure, a number of protein-protein associations involving both S. cerevisiae and human TFIIIC and TFIIIB subunits have been described, which may participate in the recruitment of TFIIIB to type 1 and 2 promoters. Thus, Tfc8 has been show to interact with Bdp1 and TBP, and the corresponding human protein TFIIIC90 with Brf1 (Hsieh et al., 1999); Tfc4 with Brf1 and Bdp1, and the corresponding human protein TFIIIC102 with Brf1 and TBP (Hsieh et al., 1999); and the human protein TFIIIC63 with Brf1 and TBP (Hsieh et al., 1999).