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Mcm2-7 proteins are generally considered to function as a heterohexameric complex, providing helicase activity for the elongation step of DNA replication. These proteins are loaded onto replication origins in M-G1 phase in a process termed licensing or pre-replicative complex formation. It is likely that Mcm2-7 proteins are loaded onto chromatin simultaneously as a pre-formed hexamer although some studies suggest that subcomplexes are recruited sequentially. To analyze this process in fission yeast, we have compared the levels and chromatin binding of Mcm2-7 proteins during the fission yeast cell cycle. Mcm subunits are present at approximately 1 x 10(4) molecules/cell and are bound with approximately equal stoichiometry on chromatin in G1/S phase cells. Using a single cell assay, we have correlated the timing of chromatin association of individual Mcm subunits with progression through mitosis. This showed that Mcm2, 4 and 7 associate with chromatin at about the same stage of anaphase, suggesting that licensing involves the simultaneous binding of these subunits. We also examined Mcm2-7 chromatin association when cells enter a G0-like quiescent state. Chromatin binding is lost in this transition in a process that does not require DNA replication or the selective degradation of specific subunits.

Original publication

DOI

10.1016/j.yexcr.2006.07.001

Type

Journal article

Journal

Exp Cell Res

Publication Date

15/10/2006

Volume

312

Pages

3360 - 3369

Keywords

Anaphase, Cell Cycle, Cell Cycle Proteins, Chromatin, DNA-Binding Proteins, Green Fluorescent Proteins, Minichromosome Maintenance Complex Component 4, Minichromosome Maintenance Complex Component 6, Minichromosome Maintenance Complex Component 7, Schizosaccharomyces, Schizosaccharomyces pombe Proteins