Interaction between PRP11 and SPP91 yeast splicing factors and characterization of a PRP9-PRP11-SPP91 complex

Several proteins are involved in the early steps of the spliceosome assembly pathway. Protein-protein interactions have been identified between two Saccharomyces cerevisiae yeast splicing factors, PRP9 and SPP91. Here it is demonstrated that protein-protein interactions occur between SPP91 and PRP11. The combination of the prp9-1 mutant and a truncated prp11 mutant exhibits a synthetic lethal phenotype, suggestive of a common biochemical defect. The PRP9 and PRP11 proteins do not interact directly, but the PRP9 and PRP11 molecules can simultaneously bind SPP91 to form a three-molecule complex. Structurally and functionally related proteins are found in mammalian cells and are associated in a single biochemical fraction. This strongly suggests that the PRP9-SPP91-PRP11 complex is a key element of the splicing machinery.