MCM2-7 proteins are essential components of prereplicative complexes that accumulate cooperatively in the nucleus during G1-phase and are required to establish, but not maintain, the S-phase checkpoint.
A prereplicative complex (pre-RC) of proteins is assembled at budding yeast origins of DNA replication during the G1-phase of the cell cycle, as shown by genomic footprinting. The proteins responsible for this prereplicative footprint have yet to be identified but are likely to be involved in the earliest stages of the initiation step of chromosome replication. Here we show that MCM2-7 proteins are essential for both the formation and maintenance of the pre-RC footprint at the origin ARS305. It is likely that pre-RCs contain heteromeric complexes of MCM2-7 proteins, since degradation of Mcm2, 3, 6, or 7 during G1-phase, after pre-RC formation, causes loss of Mcm4 from the nucleus. It has been suggested that pre-RCs on unreplicated chromatin may generate a checkpoint signal that inhibits premature mitosis during S-phase. We show that, although mitosis does indeed occur in the absence of replication if MCM proteins are degraded during G1-phase, anaphase is prevented if MCMs are degraded during S-phase. Our data indicate that pre-RCs do not play a direct role in checkpoint control during chromosome replication.
Labib
K
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ICRF Clare Hall Laboratories, South Mimms, Hertfordshire, EN6 3LD, United Kingdom.
Kearsey
S E
SE
Diffley
J F
JF
D018797:Cell Cycle Proteins / Q000235:genetics / Q000378:metabolism*; D002467:Cell Nucleus / Q000378:metabolism; D002868:Chromosomal Proteins, Non-Histone; D015825:Chromosomes, Fungal; D004261:DNA Replication; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D005656:Fungal Proteins / Q000235:genetics / Q000378:metabolism*; D016193:G1 Phase; D064148:Minichromosome Maintenance Complex Component 4; D064151:Minichromosome Maintenance Complex Component 6; D064168:Minichromosome Maintenance Complex Component 7; D008938:Mitosis / Q000502:physiology; D009687:Nuclear Proteins / Q000235:genetics / Q000378:metabolism*; D016196:S Phase; D012441:Saccharomyces cerevisiae / Q000166:cytology / Q000235:genetics / Q000378:metabolism; D029701:Saccharomyces cerevisiae Proteins; D029702:Schizosaccharomyces pombe Proteins; D015398:Signal Transduction
D018797:Cell Cycle Proteins; D002868:Chromosomal Proteins, Non-Histone; D004268:DNA-Binding Proteins; D005656:Fungal Proteins; D009687:Nuclear Proteins; D029701:Saccharomyces cerevisiae Proteins; D029702:Schizosaccharomyces pombe Proteins; C085711:mcm5 protein, S pombe; C069199:MCM2 protein, S cerevisiae; C092802:MCM4 protein, S cerevisiae; C491207:MCM6 protein, S cerevisiae; C491088:MCM7 protein, S cerevisiae; D064148:Minichromosome Maintenance Complex Component 4; D064151:Minichromosome Maintenance Complex Component 6; D064168:Minichromosome Maintenance Complex Component 7