FIG. 9.

Model for Rds3p function and Yra1p recruitment in splicing. Assembly of the splicing apparatus from the branchpoint-dependent commitment complex (CC2) through the point of mRNA release is diagrammed. For clarity's sake only a subset of the splicing-related snRNP and non-snRNP proteins are indicated. Rds3p is shown as essential for the stable addition of the U2 snRNP particle to the commitment complex in prespliceosome formation. Yra1p is presented as being either associated with the U2 snRNP or recruited independently to the spliceosome through contacts that might include both Sub2p and one or more components of the Rds3p-SF3b complex. Sometime prior to or concurrent with the Prp22p-dependent mRNA release step, components of the RNA export pathway are deposited on the processed mRNA. Rds3p likely remains stably associated with the snRNP components of the splicing apparatus, although its release with the RNA export factors cannot be ruled out.