The RecX protein interacts with the RecA protein and modulates its activity in Herbaspirillum seropedicae

C.W Galvão,J Schumacher,R.M Etto,L.S Chubatsu,M.G Yates,M Buck,F.O Pedrosa,E.M Souza,M.B.R Steffens

doi:10.1590/s0100-879x2012007500160

Abstract

DNA repair is crucial to the survival of all organisms. The bacterial RecA protein is a central component in the SOS response and in recombinational and SOS DNA repairs. The RecX protein has been characterized as a negative modulator of RecA activity in many bacteria. The recA and recX genes of Herbaspirillum seropedicae constitute a single operon, and evidence suggests that RecX participates in SOS repair. In the present study, we show that the H. seropedicae RecX protein (RecXHs) can interact with the H. seropedicae RecA protein (RecAHs) and that RecAHs possesses ATP binding, ATP hydrolyzing and DNA strand exchange activities. RecXHs inhibited 90% of the RecAHs DNA strand exchange activity even when present in a 50-fold lower molar concentration than RecAHs. RecAHs ATP binding was not affected by the addition of RecX, but the ATPase activity was reduced. When RecXHs was present before the formation of RecA filaments (RecA-ssDNA), inhibition of ATPase activity was substantially reduced and excess ssDNA also partially suppressed this inhibition. The results suggest that the RecXHs protein negatively modulates the RecAHs activities by protein-protein interactions and also by DNA-protein interactions.

Highlights

Bacterial genomic DNA is constantly subject to chemical and physical damage
In most bacterial species studied to date, including H. seropedicae, recX is found downstream and co-transcribed with the recA gene [17,20,21], but exceptions to the typical recA-recX genomic organization are found including overlapping [16] or separated genes on the chromosome regulated by their own promoters (24; Table S1)
Such phenotype was not observed in E. coli and D. radiodurans recX mutants in which RecA overexpression was not lethal (20,26; Table S1)

Summary

Introduction

Bacterial genomic DNA is constantly subject to chemical and physical damage. The repair of such damages is essential since DNA is the template for its own duplication as well as the production of diverse types of RNA and proteins [1]. Specialized enzymatic complexes are designed to avoid genetic alterations or to reduce their frequency [2]. RecA promotes the expression of proteins involved in the non-mutagenic and mutagenic DNA repair by inducing LexA repressor autocleavage [3] and promotes recombinational DNA repair by catalyzing the DNA strand exchange reaction [4]. RecA-ATP binds to the UmuD’2C complex to form the active PolV polymerase responsible for the DNA translesion synthesis or SOS mutagenesis [5]

Methods

Results

Conclusion