Catalytic activities of recA protein are dependent on the lattice length of the single-strand DNA ligand

Abstract

recA protein (RecA) performs diverse catalytic activities that require a complex with single-stranded DNA and an NTP. A subset of these functions shows optimal activity at a high DNA/protein ratio and requires NTP hydrolysis, whereas other catalytic activities are optimal in RecA-saturated complexes that require NTP, but do not hydrolyze it. To analyze the mechanism of catalytic discrimination, we investigated the properties of RecA bound to small oligonucleotides (oligos) of defined sizes. We show that RecA bound to (dT) 16 is optimal for co-protease activity and not active as ATPase whereas the complex with (dT)24 is competent in ATP hydrolysis but impaired as a co-protease. Thermodynamic measurements of the equilibrium-binding properties of these complexes showed that (dT)24 promoted a more salt sensitive complex than the one formed with (dT)16, indicating more ionic interactions between RecA and DNA in the former. X-ray pictures show that the oligo complexes form helixes. We propose that RecA may change its conformation as a function of the number of phosphates available to the monomer in the interacting DNA lattice, thus promoting an allosteric change in catalytic activities. This model offers explanations for the observed inhibition of co-protease activity by excess ssDNA. ©2008 Landes Bioscience.