Roles for ORC in M phase and S phase.
The origin recognition complex (ORC), a six-subunit protein, functions as the replication initiator in the yeast Saccharomyces cerevisiae. Initiation depends on the assembly of the prereplication complex in late M phase and activation in S phase. One subunit of ORC, Orc5p, was required at G1/S and in early M phase. Asynchronous cells with a temperature-sensitive orc5-1 allele arrested in early M phase. In contrast, cells that were first synchronized in M phase, shifted to the restrictive temperature, and then released from the block arrested at the G1/S boundary. The G1/S arrest phenotype could not be suppressed by introducing wild-type Orc5p during G1. Although all orc2 and orc5 mutations were recessive in the conventional sense, this dominant phenotype was shared with other orc5 alleles and an orc2 allele. The dominant inhibition to cell-cycle progression exhibited by the orc mutants was restricted to the nucleus, suggesting that chromosomes with mutant ORC complexes were capable of sending a signal that blocked initiation on chromosomes containing functional origins.
Dillin
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Division of Genetics, University of California at Berkeley, 401 Barker Hall, Berkeley, CA 94720, USA.
Rine
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D017489:CDC28 Protein Kinase, S cerevisiae / Q000378:metabolism; D018797:Cell Cycle Proteins; D002467:Cell Nucleus / Q000502:physiology; D015825:Chromosomes, Fungal / Q000502:physiology; D003433:Crosses, Genetic; D004261:DNA Replication; D004271:DNA, Fungal / Q000096:biosynthesis; D004268:DNA-Binding Proteins / Q000235:genetics / Q000502:physiology*; D005656:Fungal Proteins / Q000502:physiology; D005800:Genes, Fungal; D008938:Mitosis; D009154:Mutation; D051738:Origin Recognition Complex; D010641:Phenotype; D016196:S Phase; D012441:Saccharomyces cerevisiae / Q000166:cytology* / Q000235:genetics / Q000378:metabolism*; D029701:Saccharomyces cerevisiae Proteins; D013696:Temperature
D018797:Cell Cycle Proteins; D004271:DNA, Fungal; D004268:DNA-Binding Proteins; D005656:Fungal Proteins; C497215:ORC2 protein, S cerevisiae; C497220:ORC5 protein, S cerevisiae; D051738:Origin Recognition Complex; D029701:Saccharomyces cerevisiae Proteins; C069930:rad9 protein; D017489:CDC28 Protein Kinase, S cerevisiae