Nature Structural & Molecular Biology
12, 756 - 762 (2005)
Published online: 14 August 2005; | doi:10.1038/nsmb974
Organization of the archaeal MCM complex on DNA and implications for the helicase mechanismAdam T McGeoch1, 2, Michael A Trakselis1, 2, Ronald A Laskey1
& Stephen D Bell11
MRC Cancer Cell Unit, Hutchison MRC Research Centre, Hills Road, Cambridge, CB2 2XZ, UK. 2
These authors contributed equally toward this work.
Correspondence should be addressed to Stephen D Bell sb419@hutchison-mrc.cam.ac.uk The homomultimeric archaeal mini-chromosome maintenance (MCM) complex serves as a simple model for the analogous heterohexameric eukaryotic complex. Here we investigate the organization and orientation of the MCM complex of the hyperthermophilic archaeon Sulfolobus solfataricus (Sso) on model DNA substrates. Sso MCM binds as a hexamer and slides on the end of a 3'-extended single-stranded DNA tail of a Y-shaped substrate; binding is oriented so that the motor domain of the protein faces duplex DNA. Two candidate  -hairpin motifs within the MCM monomer have partially redundant roles in DNA binding. Notably, however, conserved basic residues within these motifs have nonequivalent roles in the helicase activity of MCM. On the basis of these findings, we propose a model for the mechanism of the helicase activity of MCM and note parallels with SV40 T antigen.
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