THE BUDDING YEAST U5 SNRNP PRP8 IS A HIGHLY CONSERVED PROTEIN WHICH LINKS RNA SPLICING WITH CELL-CYCLE PROGRESSION

The dbf3 mutation was originally obtained in a screen for DNA synthesi s mutants with a cell cycle phenotype in the budding yeast Saccharomyc es cerevisiae. We have now isolated the DBF3 gene and found it to be a n essential gene with an ORF of 7239 nucleotides, potentially encoding a large protein of 268 kDa. We also obtained an allele-specific high copy number suppressor of the dbf3-1 allele, encoded by the known SSB1 gene, a member of the Hsp70 family of heat shock proteins. The sequen ce of the Dbf3 protein is 58% identical over 2300 amino acid residues to a predicted protein from Caenorhabditis elegans. Furthermore, parti al sequences with 61% amino acid sequence identity were deduced from t wo files of human cDNA in the EST nucleotide database so that Dbf3 is a highly conserved protein. The nucleotide sequence of DBF3 turned out to be identical to the yeast gene PRP8, which encodes a U5 snRNP requ ired for pre-mRNA splicing. This surprising result led us to further c haracterise the phenotype of dbf3 which confirmed its role in the cell cycle and showed it to function early, around the time of S phase. Th is data suggests a hitherto unexpected link between pre-mRNA splicing and the cell cycle.