A MULTISUBUNIT COMPLEX-ASSOCIATED WITH THE RNA POLYMERASE-II CTD AND TATA-BINDING PROTEIN IN YEAST

We report genetic and biochemical evidence that the RNA polymerase II carboxy-terminal domain (CTD) interacts with a large multisubunit comp lex that contains TATA-binding protein (TBP) and is an integral part o f the transcription initiation complex. The isolation and characteriza tion of extragenic suppressors of S. cerevisiae RNA polymerase II CTD truncation mutations led us to identify SRB2, SRB4, SRB5, and SRB6 as genes involved in CTD function in vivo. SRB2 was previously isolated a nd shown to encode a 23 kd TBP-binding protein. The four SRB proteins and a portion of cellular TBP are components of a high molecular weigh t multisubunit complex that is tightly bound to RNA polymerase II. Thi s SRB-TBP complex binds specifically to recombinant CTD protein. In vi tro transcription and template commitment assays confirm that SRB2 and SRB5 are components of a functional preinitiation complex and are req uired for efficient transcription initiation.