Multiple roles for the yeast SUB2/yUAP56 gene in splicing

The UAP56 gene has been shown to be required for prespliceosome assembly in mammals. We report here the isolation of the Schizosaccharomyces pombe ort holog of this gene by heterologous complementation of a combined PRP40HA(3) /nam8 Delta defect in budding yeast. The Saccharomyces cerevisiae ortholog, YDL084w/SUB2, is also able to suppress this defect. We show that SUB2 is i nvolved in splicing in vivo as well as in vitro. Sub2 defective extracts fo rm a stalled intermediate that contains U2snRNP and can be chased into func tional spliceosomes. Our experiments also suggest a role for this protein i n events that precede prespliceosome formation. Data reported here as well as in the accompanying papers strongly implicate Sub2p in multiple steps of the spliceosome assembly process.