Cell-division-cycle defects associated with fission yeast pre-mRNA splicing mutants

We have isolated six new pre-mRNA splicing mutants (prp) from a collection of temperature-sensitive (ts-) Schizosaccharomyces pombe strains. The prp mutants are defective in the splicing of both messenger RNA and U6 small nuclear RNA precursors. A single recessive mutation is responsible for both the ts- growth and the splicing phenotypes in each of the prp mutants. The six prp mutations are unlinked and fall into separate complementation groups. Two are allelic with the previously described prp3 and prp4 mutations; the remaining four define the new alleles prp5-1, prp6-1, prp7-1, and prp9-1. The six mutants exhibit three splicing phenotypes: accumulation of unspliced precursor at the restrictive but not at the permissive temperature; accumulation of unspliced precursor at both the permissive and restrictive temperatures; and accumulation of unspliced precursor, the intron-exon lariat intermediate, and the intron lariat final product. In addition to their aberrant splicing phenotypes, the prp5-1 and prp6-1 mutants express classical cell-division-cycle defects, while prp7-1 exhibits an unusual hyphal morphology. These results suggest a connection between pre-mRNA splicing and the control of cell division in fission yeast.