TFIIF-TAF-RNA POLYMERASE-II CONNECTION

RNA polymerase transcription factor IIF (TFIIF) is required for initia tion at most, if not all, polymerase II promoters. We report here the cloning and sequencing of genes for a yeast protein that is the homolo g of mammalian TPIIF. This yeast protein, previously designated factor g, contains two subunits, Tfg1 and Tfg2, both of which are required f or transcription, essential for yeast cell viability, and whose sequen ces exhibit significant similarity to those of the mammalian factor. T he yeast protein also contains a third subunit, Tfg3, which is less ti ghtly associated and at most stimulatory to transcription, dispensable for fell viability, and has no known counterpart in mammalian TFIIF. Remarkably, the TFG3 gene encodes yeast TAF30, and furthermore, is ide ntical to ANC1, a gene implicated in actin cytoskeletal function in vi vo (Welch and Drubin 1994). Tfg3 is also a component of the recently d escribed mediator complex (Kim et al. 1994), whose interaction with th e carboxy-terminal repeat domain of RNA polymerase II enables transcri ptional activation. Deletion of TFG3 results in diminished transcripti on in vivo.