Cover: Model for the DNA-triggered conformational changes occurring within the Methanothermobacter thermautotrophicus MCM helicase. Electron microscopy single particle reconstruction of the DNA treated MCM shows a double hexameric structure displaying an unexpected asymmetry between the two rings. When the atomic coordinates of a related crystallographic structure are fitted into the map, distinct configurations can be modeled for the AAA+ (red) and the HTH (blue) domains. Shown in the first row are the cartoon models fitted into the EM electron density maps for the two rings of the MCM double hexamer. The maps generated from the fitted atomic coordinates are displayed in the second row, to highlight the nature of the conformational changes. The AAA+ domain engages in a rotation of the subunits within the ring, which is reminiscent of the nucleotide dependent iris-type motion of the SV40 large-T antigen helicase. See the paper by Costa et al. (2006), Nucleic Acids Res., 34, 5829–5838.
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