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 pre-mRNA-U1 snRNP complex (commitment complex) that forms during early spliceosome assembly in yeast extracts. Unlike U1 snRNP itself, the association of MUD2P with pre-mRNA is dependent on a proper yeast branchpoint sequence. Genetic experiments indicate that MUD2P affects U2 snRNP addition. Moreover, experiments in the two-hybrid system show that PRP11P, a recently identified component of U2 snRNP, can interact directly with MUD2P. The experiments identify a specific inter-snRNP protein-protein contact that occurs during spliceosome assembly and more generally support substantial functional similarity between U2AF65 and MUD2P.