Functional analyses of interacting factors involved in both pre-mRNA splicing and cell cycle progression in Saccharomyces cerevisiae

Through a genetic screen to search for factors that interact with Prp17/Cdc 40p, a protein involved in both cell cycle progression and pre-mRNA splicin g, we identify three novel factors, which we call Syf1p, Syf2p, and Syf3 (S Ynthetic lethal with cdc Forty), Here we present evidence that all three pr oteins are spliceosome associated, that they associate weakly or transientl y with U6 and U5 snRNAs, and that Syf1p and Syf3p (also known as Clf1p) are required for pre-mRNA splicing. In addition we show that depletion of Syf1 p or Syf3p results in cell cycle arrest at the G2/M transition. Thus, like Prp17/Cdc40p, Syf1p and Syf3p are involved in two distinct cellular process es. We discuss the likelihood that Syf1p, Syf2p, and Syf3p are components o f a protein complex that assembles into spliceosomes and also regulates cel l cycle progression.