title: Cell cycle execution point analysis of ORC function and characterization of the checkpoint response to ORC inactivation in Saccharomyces cerevisiae.
abstract: Chromosomal replication initiates through the assembly of a prereplicative complex (pre-RC) at individual replication origins in the G1-phase, followed by activation of these complexes in the S-phase. In Saccharomyces cerevisiae, the origin recognition complex (ORC) binds replication origins throughout the cell cycle and participates in pre-RC assembly. Whether the ORC plays an additional role subsequent to pre-RC assembly in replication initiation or any other essential cell cycle process is not clear. To study the function of the ORC during defined cell cycle periods, we performed cell cycle execution point analyses with strains containing a conditional mutation in the ORC1, ORC2 or ORC5 subunit of ORC. We found that the ORC is essential for replication initiation, but is dispensable for replication elongation or later cell cycle events. Defective initiation in ORC mutant cells results in incomplete replication and mitotic arrest enforced by the DNA damage and spindle assembly checkpoint pathways. The involvement of the spindle assembly checkpoint implies a defect in kinetochore-spindle attachment or sister chromatid cohesion due to incomplete replication and/or DNA damage. Remarkably, under semipermissive conditions for ORC1 function, the spindle checkpoint alone suffices to block proliferation, suggesting this checkpoint is highly sensitive to replication initiation defects. We discuss the potential significance of these overlapping checkpoints and the impact of our findings on previously postulated role(s) of ORCs in other cell cycle functions.
authors.affiliation: Molecular and Computational Biology Program, Department of Biological Sciences, University of Southern California, Los Angeles, California 90089-2910, USA.
authors.forename: Daniel G
authors.initials: DG
authors.lastname: Gibson
authors.forename: Stephen P
authors.initials: SP
authors.lastname: Bell
authors.forename: Oscar M
authors.initials: OM
authors.lastname: Aparicio
mesh_terms: D000483:Alleles; D002453:Cell Cycle / Q000502:physiology*; D018797:Cell Cycle Proteins / Q000235:genetics / Q000378:metabolism; D064447:Checkpoint Kinase 2; D004249:DNA Damage / Q000235:genetics; D004271:DNA, Fungal / Q000378:metabolism; D020868:Gene Silencing; D008938:Mitosis; D009154:Mutation; D051738:Origin Recognition Complex / Q000235:genetics* / Q000378:metabolism*; D017346:Protein Serine-Threonine Kinases / Q000235:genetics / Q000378:metabolism; D021122:Protein Subunits; D012441:Saccharomyces cerevisiae / Q000166:cytology* / Q000235:genetics; D029701:Saccharomyces cerevisiae Proteins / Q000235:genetics / Q000378:metabolism; D008941:Spindle Apparatus / Q000235:genetics / Q000378:metabolism
chemical_list: D018797:Cell Cycle Proteins; D004271:DNA, Fungal; D051738:Origin Recognition Complex; D021122:Protein Subunits; D029701:Saccharomyces cerevisiae Proteins; C069930:rad9 protein; D064447:Checkpoint Kinase 2; D017346:Protein Serine-Threonine Kinases; C067022:RAD53 protein, S cerevisiae