spp42, Identified as a Classical Suppressor of prp4-73, Which Encodes a Kinase Involved in Pre-mRNA Splicing in Fission Yeast, Is a Homologue of the Splicing Factor Prp8p

We have identified two classical extragenic suppressors, spp41 and spp42, of the temperature sensitive (ts) allele prp4-73. The prp4+ gene of Schizosaccharomyces pombe encodes a protein kinase. Mutations in both suppressor genes suppress the growth and the pre-mRNA splicing defect of prp4-73ts at the restrictive temperature (36°). spp41 and spp42 are synthetically lethal with each other in the presence of prp4-73ts, indicating a functional relationship between spp41 and spp42. The suppressor genes were mapped on the left arm of chromosome I proximal to the his6 gene. Based on our mapping data we isolated spp42 by screening PCR fragments for functional complementation of the prp4-73ts mutant at the restrictive temperature. spp42 encodes a large protein (p275), which is the homologue of Prp8p. This protein has been shown in budding yeast and mammalian cells to be a bona fide pre-mRNA splicing factor. Taken together with other recent genetic and biochemical data, our results suggest that Prp4 kinase plays an important role in the formation of catalytic spliceosomes.