Official websites use. Share sensitive information only on official, secure websites. Corresponding author. Phone: 33 1 69 08 37 Fax: 33 1 69 08 47 E-mail: conesa matthieu. The protein sequence of C17 encoded by RPC17 is conserved from yeasts to humans. However, mammalian homologues of C17 named CGRP-RCP are known to be involved in a signal transduction pathway related to G protein-coupled receptors, not in transcription. C17 and C25 were found to interact genetically in suppression screens and physically in coimmunopurification and two-hybrid experiments.
These RNA polymerase subunits appear to have evolved to meet the distinct requirements of the multiple forms of RNA polymerases. Transcription of eukaryotic genes is mediated by three related forms of nuclear RNA polymerases Pol. These enzymes are large multisubunit proteins that require a distinct set of general transcription factors to transcribe their cognate genes 58 , In the well-studied case of the yeast Saccharomyces cerevisiae , the three enzymes contain 14 Pol I , 12 Pol II , and 17 Pol III different subunits and share a set of 5 conserved and 5 common subunits 9 , All but one of these subunits are represented in the archaeal enzyme 15 , In Pol II, this subunit core enzyme is competent for the transcription of nonspecific DNA templates 16 but not for promoter-dependent transcription The atomic structure of the yeast core Pol II enzyme has been recently determined Genetic and biochemical studies have shed light on the function of some Pol III-specific subunits.
One of these polypeptides, yeast C34, has been mapped the furthest upstream on the promoter 5 and shown to have a dual role in Pol III recruitment and in open complex formation via its interaction with the Brf1 component of TFIIIB 7 , 30 , This subcomplex of Pol III subunits is therefore thought to play a role in preinitiation complex recognition.
While the role of C17 as an essential subunit of yeast Pol III was well established on genetic and biochemical grounds, it was surprising that the putative mammalian homologue, based on sequence comparison with yeast C17, was known as a hormone receptor component 19 , Two other subunits, C37 and C53, specifically interact in a two-hybrid assay 21 and are essential for transcription in vivo 9 but their precise roles are unknown.
The present study deals with two components of Pol III, C17 and C25, that are essential for growth and structurally conserved from yeast to humans 20 , Rpb7 forms with Rpb4 a stable complex that can be reversibly dissociated from the yeast Pol II enzyme 16 , 18 , Rpb4, which is dispensable in S. Interestingly, Rpb4 is essential in Schizosaccharomyces pombe and was shown to interact with the phosphatase Fcp1 32 , Low-resolution three-dimensional maps of yeast Pol II, lacking or not lacking subunits Rpb4 and Rpb7, suggested that these two subunits form part of the floor of the DNA-binding cleft We show here that C17 is akin to Rpb4 and RpoF and specifically interacts with C25, thus underscoring the remarkable conservation of this heterodimeric structure throughout archaeal and eukaryotic evolution.
