DNA unwinding activity for exterior waist mutants. Representative DNA unwinding time courses for SsoMCM mutants K111A/R113A (A), K129A (B), and R226A (C) (at 2.4 μm) from 10 to 30 min. Shown is fork DNA with a 30-base duplex and 32P-labeled at the 5′-end of the translocating strand. D, plots of the unwinding rates for the waist mutants (K323A/R440A (green), K111A/R113A (pink), K129A (red), and R226A (russet)) compared with wild type (blue) quantified as the average from at least three separate experiments. Error bars, S.E. from at least three unwinding experiments.