Figure 2.

Proposed mechanism for processive DNA unwinding by RecBCD helicase. RecBCD initially binds to the blunt end of a duplex DNA and couples its favorable free energy of binding to melt 4–6 bp of the duplex DNA in an ATP-independent manner. RecBCD then translocates along the resulting ssDNA tracks hydrolyzing 1 ATP/motor/nucleotide until it reaches the new ss/ds DNA junction. ATP binding/hydrolysis resets the enzyme so that RecBCD can melt another 4–6 bp and then translocate along the newly formed ssDNA tracks. These DNA melting and ssDNA translocation steps are repeated during processive DNA unwinding.