Dependence of pre-mRNA introns on PRP17, a non-essential splicing factor: implications for efficient progression through cell cycle transitions

Abstract

Saccharomyces cerevisiaePRP17 (CDC40) encodes a second-step pre-mRNA splicing factor with a role in cell division. The functions of Prp17 in specific cell cycle transitions were examined using temperature-sensitive alleles in arrest/release experiments. We find that G₁/S and G₂/M transitions depend on Prp17. G₁-synchronized prp17::LEU2 cells arrest at non-permissive temperatures as unbudded haploid cells with low levels of CLN1, CLB5 and RNR1 transcripts. This indicates a Prp17 execution point at or prior to Start. Reduced levels of α-tubulin protein, a mitotic spindle component, underlie the benomyl sensitivity of prp17 mutants and possibly their G₂/M arrest. Splicing of TUB1 and TUB3 transcripts, which encode α-tubulin, was analyzed in prp17 and other second-step factor mutants. TUB1 splicing is inefficient in prp17, prp16 and prp22, and marginally affected in prp18, slu7-1 and psf1-1. TUB3 splicing is similarly affected. In vitro splicing with TUB3 pre-mRNA demonstrates a compromised second step in prp17::LEU2 extracts, implicating a direct role for Prp17 in its efficient splicing. Genomic replacement of an intronless TUB1 gene relieves the benomyl sensitivity of prp17 mutants; however, they remain temperature sensitive, implying multiple limiting factors for mitosis. The data suggest that integration of splicing with the cell cycle is important for G₁/S and G₂/M transitions.