CELL-DIVISION CYCLE DEFECTS ASSOCIATED WITH FISSION YEAST PRE-MESSENGER-RNA SPLICING MUTANTS

We have isolated six new pre-mRNA splicing mutants (prp) from a collec tion of temperature-sensitive (ts(-)) Schizosaccharomyces pombe strain s. The prp mutants are defective in the splicing of both messenger RNA and U6 small nuclear RNA precursors. A single recessive mutation is r esponsible 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 d escribed prp3 and prp4 mutations; the remaining four define the new al leles prp5-1, prp6-1, prp7-1, and prp9-1. The six mutants exhibit thre e splicing phenotypes: accumulation of unspliced precursor at the rest rictive but not at the permissive temperature; accumulation of unsplic ed precursor at both the permissive and restrictive temperatures; and accumulation of unspliced precursor, the intron-exon lariat intermedia te, 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 m orphology. These results suggest a connection between pre-mRNA splicin g and the control of cell division in fission yeast.