Figure 3.

E.coli RecQ is comparably active on G4 DNA and duplex DNA. (A) Unwinding assay of E.coli RecQ on G4 and duplex DNA substrates. ³²P-labeled DNAs (5 nM) were incubated with RecQ at 0, 2, 5, 10 and 50 nM. (B) Competitive inhibition of unwinding. Top, ³²P-labeled G4 DNA (5 nM) was incubated with RecQ (50 nM) and indicated amounts of unlabeled duplex DNA. Bottom, ³²P-labeled duplex DNA (5 nM) was incubated with RecQ (50 nM) and indicated amounts of unlabeled G4 DNA competitor. (C) Inhibition of RecQ duplex and G4 DNA unwinding activity by competitor DNAs. Data from (B) were quantified by phosphoimager, and protein activity expressed as the fraction of labeled G4 DNA (filled circles) and duplex DNA (open circles) unwound during the course of the assay.