title: Evidence that a free-running oscillator drives G1 events in the budding yeast cell cycle.
abstract: In yeast and somatic cells, mechanisms ensure cell-cycle events are initiated only when preceding events have been completed. In contrast, interruption of specific cell-cycle processes in early embryonic cells of many organisms does not affect the timing of subsequent events, indicating that cell-cycle events are triggered by a free-running cell-cycle oscillator. Here we present evidence for an independent cell-cycle oscillator in the budding yeast Saccharomyces cerevisiae. We observed periodic activation of events normally restricted to the G1 phase of the cell cycle, in cells lacking mitotic cyclin-dependent kinase activities that are essential for cell-cycle progression. As in embryonic cells, G1 events cycled on schedule, in the absence of S phase or mitosis, with a period similar to the cell-cycle time of wild-type cells. Oscillations of similar periodicity were observed in cells responding to mating pheromone in the absence of G1 cyclin (Cln)- and mitotic cyclin (Clb)-associated kinase activity, indicating that the oscillator may function independently of cyclin-dependent kinase dynamics. We also show that Clb-associated kinase activity is essential for ensuring dependencies by preventing the initiation of new G1 events when cell-cycle progression is delayed.
authors.affiliation: Department of Molecular Biology, The Scripps Research Institute, La Jolla, California 94303, USA.
authors.forename: S B
authors.initials: SB
authors.lastname: Haase
authors.forename: S I
authors.initials: SI
authors.lastname: Reed
mesh_terms: D017489:CDC28 Protein Kinase, S cerevisiae / Q000378:metabolism; D019926:Cyclin B / Q000502:physiology; D018844:Cyclin-Dependent Kinases / Q000378:metabolism; D016213:Cyclins / Q000502:physiology; D004261:DNA Replication; D004271:DNA, Fungal / Q000096:biosynthesis; D005656:Fungal Proteins / Q000502:physiology; D016193:G1 Phase / Q000502:physiology*; D010507:Periodicity; D004718:Saccharomycetales / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D008941:Spindle Apparatus / Q000502:physiology; D014158:Transcription, Genetic
chemical_list: D019926:Cyclin B; D016213:Cyclins; D004271:DNA, Fungal; D005656:Fungal Proteins; D017489:CDC28 Protein Kinase, S cerevisiae; D018844:Cyclin-Dependent Kinases