Synergy between RecBCD subunits is essential for efficient DNA unwinding.

Area of Science:

• Molecular biology
• Biophysics
• Enzymology

Background:

• The bacterial RecBCD enzyme is crucial for DNA double-strand break repair.
• RecBCD rapidly unwinds DNA and displaces DNA-binding proteins, indicating force generation.
• The individual roles of RecBCD subunits in force generation remain unclear.

Purpose of the Study:

• To investigate the force generation capabilities of individual RecBCD subunits within the intact complex.
• To elucidate the mechanism of DNA unwinding by the RecD subunit.

Main Methods:

• Development of a novel optical tweezers assay to monitor RecBCD subunit activity.
• Measurement of forces and velocities generated by RecBCD and its subunits.
• Experiments conducted across a range of ATP concentrations and applied forces.

Main Results:

• RecBCD and its subunits can generate forces of 25-40 pN without compromising velocity.
• The isolated RecD subunit exhibits rapid translocation but weak, less processive helicase activity.
• RecD appears to function as a Brownian ratchet, with ATP binding rectifying its unwinding activity.

Conclusions:

• The RecBCD complex generates significant forces essential for its DNA repair function.
• The RecD subunit's mechanism is a force-generating Brownian ratchet, regulated by ATP.
• Other RecBCD subunits influence RecD's ratchet equilibrium, optimizing its function within the complex.