AN ESSENTIAL COMPONENT OF A C-TERMINAL DOMAIN PHOSPHATASE THAT INTERACTS WITH TRANSCRIPTION FACTOR IIF IN SACCHAROMYCES-CEREVISIAE

One of the essential components of a phosphatase that specifically dep hosphorylates the Saccharomyces cerevisiae RNA polymerase II (RPII) la rge subunit C-terminal domain (CTD) is a novel polypeptide encoded by an essential gene termed FCP1, The Fcp1 protein is localized to the nu cleus, and it binds the largest subunit of the yeast general transcrip tion factor IIF (Tfg1), In vitro, transcription factor IIF stimulates phosphatase activity in the presence of Fcp1 and a second complementin g fraction, Two distinct regions of Fcp1 are capable of binding to Tfg 1, but the C-terminal Tfg1 binding domain is dispensable for activity in vivo and in vitro, Sequence comparison reveals that residues 173-35 7 of Fcp1 correspond to an amino acid motif present in proteins of unk nown function predicted in many organisms.