title: Fission yeast cdc21, a member of the MCM protein family, is required for onset of S phase and is located in the nucleus throughout the cell cycle.
abstract: The fission yeast cdc21 protein belongs to the MCM family, implicated in the once per cell cycle regulation of chromosome replication. In budding yeast, proteins in this family are eliminated from the nucleus during S phase, which has led to the suggestion that they may serve to distinguish unreplicated from replicated DNA, as in the licensing factor model. We show here that, in contrast to the situation in budding yeast, cdc21 remains in the nucleus after S phase, as is found for related proteins in mammalian cells. We suggest that regulation of nuclear import of these proteins may not be an essential aspect of their function in chromosome replication. To determine the function of cdc21+, we have analysed the phenotype of a gene deletion. cdc21+ is required for entry into S phase and, unexpectedly, a proportion of cells depleted of the gene product are able to enter mitosis in the absence of DNA replication. These results are consistent with the view that individual proteins in the MCM family are required for all initiation events, and defective initiation may impair the coordination between mitosis and S phase.
authors.affiliation: Department of Zoology, University of Oxford, UK.
authors.forename: D
authors.initials: D
authors.lastname: Maiorano
authors.forename: G B
authors.initials: GB
authors.lastname: Van Assendelft
authors.forename: S E
authors.initials: SE
authors.lastname: Kearsey
mesh_terms: D000818:Animals; D001483:Base Sequence; D002453:Cell Cycle; D018797:Cell Cycle Proteins / Q000502:physiology*; D002467:Cell Nucleus / Q000378:metabolism; D017931:DNA Primers / Q000737:chemistry; D004261:DNA Replication; D004268:DNA-Binding Proteins; D005260:Female; D005656:Fungal Proteins / Q000502:physiology; D017353:Gene Deletion; D015966:Gene Expression Regulation, Fungal; D005800:Genes, Fungal; D008297:Male; D051379:Mice; D064148:Minichromosome Maintenance Complex Component 4; D008969:Molecular Sequence Data; D005810:Multigene Family; D009687:Nuclear Proteins / Q000502:physiology; D012333:RNA, Messenger / Q000235:genetics; D051381:Rats; D016196:S Phase; D012568:Schizosaccharomyces / Q000166:cytology*; D029702:Schizosaccharomyces pombe Proteins
chemical_list: D018797:Cell Cycle Proteins; D017931:DNA Primers; D004268:DNA-Binding Proteins; D005656:Fungal Proteins; D009687:Nuclear Proteins; D012333:RNA, Messenger; D029702:Schizosaccharomyces pombe Proteins; D064148:Minichromosome Maintenance Complex Component 4; C078490:mcm4 protein, S pombe