title: Identification of a G1-type cyclin puc1+ in the fission yeast Schizosaccharomyces pombe.
abstract: In rapidly growing cells of the budding yeast Saccharomyces cerevisiae, the cell cycle is regulated chiefly at Start, just before the G1-S boundary, whereas in the fission yeast Schizosaccharomyces pombe, the cycle is predominantly regulated at G2-M. Both control points are present in both yeasts, and both require the p34cdc2 protein kinase. At G2-M, p34cdc2 kinase activity in S. pombe requires a B-type cyclin in a complex with p34cdc2; this complex is the same as MPF (maturation promoting factor). The p34cdc2 activity at the G1-S transition in S. cerevisiae may be regulated by a similar cyclin complex, using one of the products of a new class of cyclin genes (CLN1, CLN2 and WHI1 (DAF1/CLN3)). At least one is required for progression through the G1-S phase, and deletion of all three leads to G1 arrest. WHI1 was isolated as a dominant allele causing budding yeast cells to divide at a reduced size and was later independently identified as DAF1, a dominant allele of which rendered the cells refractory to the G1-arrest induced by the mating pheromone alpha-factor. The dominant alleles are truncations thought to yield proteins of increased stability, and the cells are accelerated through G1. Without WHI1 function, the cells are hypersensitive to alpha-factor, enlarged and delayed in G1. Heretofore, this G1-class of cyclins has not been identified in other organisms. We have isolated a G1-type cyclin gene called puc1+ from S. pombe, using a functional assay in S. cerevisiae. Expression of puc1+ in S. pombe indicates that it has a cyclin-like role in the fission yeast distinct from the role of the B-type mitotic cyclin.
authors.affiliation: Biochemistry Department, Oxford University, UK.
authors.forename: S L
authors.initials: SL
authors.lastname: Forsburg
authors.forename: P
authors.initials: P
authors.lastname: Nurse
mesh_terms: D000595:Amino Acid Sequence; D001483:Base Sequence; D015152:Blotting, Northern; D002455:Cell Division; D016213:Cyclins / Q000235:genetics* / Q000502:physiology; D005434:Flow Cytometry; D015870:Gene Expression; D008969:Molecular Sequence Data; D012441:Saccharomyces cerevisiae / Q000235:genetics*; D012568:Schizosaccharomyces / Q000235:genetics*; D012689:Sequence Homology, Nucleic Acid; D014169:Transformation, Bacterial
chemical_list: D016213:Cyclins