A HIGHLY CONSERVED DOMAIN OF RNA-POLYMERASE-II SHARES A FUNCTIONAL ELEMENT WITH ACIDIC ACTIVATION DOMAINS OF UPSTREAM TRANSCRIPTION FACTORS

We report here that the largest subunit of yeast RNA polymerase II con tains an acidic domain that is similar to acidic activators of transcr iption. This domain includes the highly conserved homology box H. A hy brid protein; containing this acidic domain fused to the DNA-binding d omain of GAL4 is a potent activator of transcription in the yeast Sacc haromyces cerevisiae. Interestingly, mutations that reduce the upstrea m activating activity of this acidic domain also abolish the normal fu nction of RNA polymerase II. Such functional defects can be rescued by the acidic activation domains of VP16 and GAL4 when inserted into the mutant derivatives of RNA polymerase II. We further show that this ac idic domain of RNA polymerase II interacts directly with two general t ranscription factors, the TATA-binding protein and TFIIB, and that the acidic activation domain of VP16 can compete specifically with the ac idic domain of the RNA polymerase for these interactions: We discuss t he implications of this finding for the mechanisms of transcriptional activation in eucaryotes.