Communication between DNA and nucleotide binding sites facilitates stepping by the RecBCD helicase.

Double-strand DNA breaks are the severest type of genomic damage, requiring rapid response to ensure survival. RecBCD helicase in prokaryotes initiates processive and rapid DNA unzipping, essential for break repair. The energetics of RecBCD during translocation along the DNA track are quantitatively not defined.

Auxiliary ATP binding sites support DNA unwinding by RecBCD.

The RecBCD helicase initiates double-stranded break repair in bacteria by processively unwinding DNA with a rate approaching ∼1,600 bp·s, but the mechanism enabling such a fast rate is unknown. Employing a wide range of methodologies - including equilibrium and time-resolved binding experiments, ensemble and single-molecule unwinding assays, and crosslinking followed by mass spectrometry - we reveal the existence of auxiliary binding sites in the RecC subunit, where ATP binds with lower affinity and distinct chemical interactions as compared to the known catalytic sites. The essentiality and functionality of these sites are demonstrated by their impact on the survival of E.

Synergy between RecBCD subunits is essential for efficient DNA unwinding.

The subunits of the bacterial RecBCD act in coordination, rapidly and processively unwinding DNA at the site of a double strand break. RecBCD is able to displace DNA-binding proteins, suggesting that it generates high forces, but the specific role of each subunit in the force generation is unclear. Here, we present a novel optical tweezers assay that allows monitoring the activity of RecBCD's individual subunits, when they are part of an intact full complex.

Interdependent Nutrient Availability and Steroid Hormone Signals Facilitate Root Growth Plasticity.

Plants acquire essential elements from inherently heterogeneous soils, in which phosphate and iron availabilities vary. Consequently, plants have developed adaptive strategies to cope with low iron or phosphate levels, including alternation between root growth enhancement and attenuation. How this adaptive response is achieved remains unclear.