A Novel Subunit of Yeast RNA Polymerase III Interacts with the TFIIB-Related Domain of TFIIIB70

Abstract

There is limited information on how eukaryotic RNA polymerases (Pol) recognize their cognate preinitiation complex. We have characterized a polypeptide copurifying with yeast Pol III. This protein, C17, was found to be homologous to a mammalian protein described as a hormone receptor. Deletion of the corresponding gene,RPC17, was lethal and its regulated extinction caused a selective defect in transcription of class III genes in vivo. Two-hybrid and coimmunoprecipitation experiments indicated that C17 interacts with two Pol III subunits, one of which, C31, is important for the initiation reaction. C17 also interacted with TFIIIB70, the TFIIB-related component of TFIIIB. The interaction domain was found to be in the N-terminal, TFIIB-like half of TFIIIB70, downstream of the zinc ribbon and first imperfect repeat. Although Pol II similarly interacts with TFIIB, it is notable that C17 has no similarity to any Pol II subunit. The data indicate that C17 is a novel specific subunit of Pol III which participates together with C34 in the recruitment of Pol III by the preinitiation complex.

ACKNOWLEDGMENTS

We thank Michel Riva and Françoise Bouet for help in peptide microsequencing, Christian Mark for assistance in sequence analysis, Emmanuel Favry for technical support, and Marc Vigneron for his generous gift of strain YGVS003. G.P. was supported by a fellowship from the French Ministère de l'Enseignement Supérieur et de la Recherche.