A CONNECTION BETWEEN PRE-MESSENGER-RNA SPLICING AND THE CELL-CYCLE INFISSION YEAST - CDC28(-DEPENDENT ATPASE() IS ALLELIC WITH PRP8(+) ANDENCODES AN RNA)HELICASE/

The fission-yeast gene cdc28(+) was originally identified in a screen for temperature-sensitive mutants that exhibit a cell-division cycle a rrest and was found to be required for mitosis. We undertook a study o f this gene to understand more fully the general requirements for entr y into mitosis. Cells carrying the conditional lethal cdc28-P8 mutatio n divide once and arrest in G2 after being shifted to the restrictive temperature. We cloned the cdc28(+) gene by complementation of the tem perature-sensitive growth arrest in cdc28-P8. DNA sequence analysis in dicated that cdc28 encodes a member of the DEAH-box family of putative RNA-dependent ATPases or helicases. The Cdc28 protein is most similar to the Prp2, Prp16, and Prp22 proteins from budding yeast, which are required for the splicing of mRNA precursors. Consistent with this sim ilarity, the cdc28-P8 mutant accumulates unspliced precursors at the r estrictive temperature. Independently, we isolated a temperature-sensi tive pre-mRNA splicing mutant prp8-1 that exhibits a cell-cycle phenot ype identical to that of cdc28-P8. We have shown that cdc28 and prp8 a re allelic. These results suggest a connection between pre-mRNA splici ng and progression through the cell cycle.