Evidence that Myb-related CDC5 proteins are required for pre-mRNA splicing

The conserved CDC5 family of Myb-related proteins performs an essential fun ction in cell cycle control at G(2)/M. Although c-Myb and many Myb-related proteins act as transcription factors, herein, we implicate CDC5 proteins i n pre-mRNA splicing. Mammalian CDC5 colocalizes with pre-mRNA splicing fact ors in the nuclei of mammalian cells, associates with core components of th e splicing machinery in nuclear extracts, and interacts with the spliceosom e throughout the splicing reaction in vitro. Furthermore, genetic depletion of the homolog of CDC5 in Saccharomyces cerevisiae, CEF1. blocks the first step of pre-mRNA processing in vivo. These data provide evidence that euka ryotic cells require CDC5 proteins for pre-mRNA splicing.