Processive DNA helicase activity of the minichromosome maintenance proteins 4, 6, and 7 complex requires forked DNA structures.

The minichromosome maintenance (Mcm) proteins 2-7 are required for both the initiation and elongation steps of chromosomal DNA replication. Previous studies have shown that the Mcm complex consisting of the Mcm 4, 6, and 7 proteins contains 3' to 5' DNA helicase activity with limited processivity (displacing duplex DNA regions ...
up to 30 nt). In this report, we show that the presence of both 5' and 3' single-stranded tails in DNA helicase substrates is essential for the processive helicase activity of the Mcm complex. The presence of both 5' and 3' tails facilitated the formation of double heterohexameric complexes of Mcm4/6/7 on substrate DNA, which appeared to be essential for the processive helicase activity. The double heterohexameric complex of Mcm4/6/7, in the presence of a single-strand DNA binding protein, is capable of unwinding duplex DNA region of about 600 bp in length. These results support the hypothesis that the Mcm4/6/7 complex can function as a replication helicase.
Mesh Terms:
Cell Cycle Proteins, Centrifugation, Density Gradient, Chromosomal Proteins, Non-Histone, Cross-Linking Reagents, DNA, DNA Helicases, DNA-Binding Proteins, Electrophoresis, Agar Gel, Enzyme Activation, Macromolecular Substances, Nuclear Proteins, Nucleic Acid Conformation, Protein Binding, Recombinant Proteins, Saccharomyces cerevisiae Proteins, Schizosaccharomyces, Substrate Specificity
Proc. Natl. Acad. Sci. U.S.A.
Date: Jan. 02, 2001
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