A protein-protein interaction map of yeast RNA polymerase III

The structure of the yeast RNA polymerase (pol) III was investigated by exh austive two-hybrid screening using a library of random genomic fragments fu sed to the Gal4 activation domain. This procedure allowed us to identify co ntacts between individual polypeptides, localize the contact domains, and d educe a protein-protein interaction map of the multisubunit enzyme, In all but one case, pol III subunits were able to interact in vivo with one or so metimes two partner subunits of the enzyme or with subunits of TFIIIC. Four subunits that are common to pol I, II, and III (ABC27, ABC14.5, ABC10 alph a, and ABC10 beta), two that are common to pol I and II. (AC40 and AC19), a nd one pol III-specific subunit (C11) can associate with defined regions of the two large subunits. These regions overlapped with highly conserved dom ains. C53, a pol III-specific subunit, interacted with a 37-kDa polypeptide that copurifies with the enzyme and therefore appears to be a unique pol I II subunit (C37). Together with parallel interaction studies based on dosag e-dependent suppression of conditional mutants, our data suggest a model of the pol III preinitiation complex.