Figure 3.

TFIIB associates with essential proteins before reaching the promoter. Wild-type and mutant forms of TFIIB expressed at high levels from the ADH1 promoter were examined for their effect on transcription activated by TFIIB–Myc and Max–RFX (lanes 4–6), or by VP16–RFX (lane 8). The TFIIB mutants carry either the C48S substitution that compromises interaction of TFIIB with pol II–TFIIF (39–42) (lane 4), or the double amino acid change F189R/G204R on the surface of the protein that contacts TBP (38) (lane 5). The strains containing TFIIB–Myc are deleted for the chromosomal TFIIB gene. The amounts of TFIIB proteins expressed in these cells were determined by the protein immunobloting shown at the bottom.