Mutations in
genes of Saccharomyces cerevisiae encoding pre-mRNA splicing factors cause
cell cycle arrest.
Orna Dahan,
Martin Kupiec
Mol. Micro. and Biotech., Tel Aviv University, Ramat Aviv, Tel Aviv, 69978,
Israel (ornad@post.tau.ac.il)
The timing of events in the cell cycle is of crucial importance, as any error can lead to cell death or cancerous growth. By using two-hybrid screens and genetic analysis we uncovered the existence of a protein complex (named CSC) which is involved in two distinct and fundamental cellular pathways: the G2/M cell cycle transition and the pre-mRNA splicing reaction. This suggests an intriguing connection between cell cycle control and splicing. By analyzing the genetic interactions of ISY1, SYF2 and NTC20, three nonessential components of the CSC, we gained insights into the role of this important complex. We demonstrated that the double mutant isy1 syf2 shows a temperature-dependent G2/M cell cycle arrest. This arrest was due to a defect in the splicing of pre-mRNA of TUB1 and TUB3, the two intron-containing genes encoding alpha-tubulin in yeast. Reduced splicing efficiency results in low levels of alpha-tubulin in isy1 syf2 cells which triggers the activation of the spindle checkpoint, causing cell cycle arrest. Cell cycle progression, however, is not exclusively dependent on the splicing of the TUB genes. In the case of another second step splicing factor, Cdc40/Prp17, the G2/M cell cycle arrest of mutant cells is caused by inefficient splicing of a different intron-containing target gene. Contrary to the arrest of CSC mutants, cdc40/prp17 arrest is not mediated by checkpoint activation. We present models of the mechanism that link cell cycle progression and splicing.