Mutations in genes of Saccharomyces cerevisiae encoding pre-mRNA splicing factors cause cell cycle arrest through activation of the spindle checkpoint.

Previous work has identified a group of genes whose products play important roles in two seemingly unrelated processes: cell cycle progression and splicing. The products of these genes show a network of physical and genetic interactions suggestive of the existence of a protein complex, the cell cycle and splicing complex (CSC). Here we analyze the genetic interactions between ISY1, SYF2 and NTC20, three non-essential components of the CSC. We show that mutations in ISY1 cause lethality in the absence of Ntc20p, and that the double mutant isy1Delta syf2Delta shows a temperature-dependent cell cycle arrest. This arrest is due to lower levels of alpha-tubulin, a protein encoded by TUB1 and TUB3, two intron-containing genes. We show that the low levels of alpha-tubulin in isy1Delta syf2Delta trigger activation of the spindle checkpoint, causing cell cycle arrest. Thus, our results have uncovered an unexpected role for pre-mRNA splicing in the maintenance of the fidelity of chromosome transmission during cell division.