THE YEAST MUD2 PROTEIN - AN INTERACTION WITH PRP11 DEFINES A BRIDGE BETWEEN COMMITMENT COMPLEXES AND U2 SNRNP ADDITION

In characterizing a series of yeast (Saccharomyces cerevisiae) mutants synthetic lethal with U1 RNA, we have identified a yeast gene (MUD2) with sequence similarity to the well-studied metazoan splicing factor U2AF65. The biochemical characterization indicates that the MUD2 gene product (MUD2P) contacts pre-mRNA directly and is a component of the p re-mRNA-U1 snRNP complex (commitment complex) that forms during early spliceosome assembly in yeast extracts. Unlike U1 snRNP itself, the as sociation of MUD2P with pre-mRNA is dependent on a proper yeast branch point sequence. Genetic experiments indicate that MUD2P affects U2 snR NP addition. Moreover, experiments in the two-hybrid system show that PRP11P, a recently identified component of U2 snRNP, can interact dire ctly with MUD2P. The experiments identify a specific inter-snRNP prote in-protein contact that occurs during spliceosome assembly and more ge nerally support substantial functional similarity between U2AF65 and M UD2P.