Figure 2.

Helicase assays. (A) Unwinding of a 21-bp DNA fragment by RecB_1–929 and reconstituted RecB_1–929C (Left) and by RecB and reconstituted RecBC (Right). (B) Unwinding of ClaI-digested [5′-³²P]pBR322χ⁺FH by using the indicated enzymes and 50 nM RecBC (lane 13), 10 nM RecBChD (lane 14), and 1 nM RecBCD (lane 15). Each reaction contained 2 nM DNA molecules and 5 mM ATP, with the indicated Mg²⁺ concentration in buffer A. Aliquots were analyzed by electrophoresis on a 1% agarose gel. Lane 16 (M), χ-markers: ClaI-digested [5′-³²P]pBR322 χ⁺FH, cleaved again with AvaI and then heat-denatured. The AvaI sites are 75 nt away from χF and 13 nt away from χH. Lane 17 (ss), heat-denatured ClaI-digested [5′-³²P]pBR322 χ⁺FH.