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Figure 4.
Two possible DNA unwinding modes by MCM helicase. (A)
Schematic representation of a MCM hexamer helicase. The 4
β-hairpins (NT, H2I, PS1, and EXT hairpins) are represented by
short solid bars; the central channel and the side channels are
in darker shades. (B) Steric exclusion model for a
single-hexameric MCM helicase. (C) Side-channel extrusion model,
showing ssDNA extruding from the side channel. DNA is shown as
black lines. Arrows indicate direction of helicase movement.
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