PMC:1140370 / 18424-19199 JSONTXT

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In contrast, only the substrate containing a 3 single-stranded DNA tail (A-fork[5]) was efficiently unwound and A-fork[3] or A-fork[3,5], was not unwound by Mcm4/6/7 (Figure 4B). Absence of helicase actions on A-fork[3,5] composed only of duplex regions is expected since double-stranded DNA is not able to activate the ATPase activity of Mcm4/6/7 (10). In contrast, the PriA, a structure-specific helicase used as a control, binds at the fork junction and unwinds the fork and the nascent lagging strand DNA on A-fork[5], or unwinds the nascent lagging strand on A-fork[3,5], as reported before (25). These results indicate that the Mcm4/6/7 complex binds to single-stranded DNA and that its helicase is activated only in the presence of a single-stranded 3-tail.