The DinI and RecX Proteins Are Competing Modulators of RecA Function

Shelley L Lusetti,Julia C Drees,Elizabeth A Stohl,H Steven Seifert,Michael M Cox

doi:10.1074/jbc.m410371200

Shelley L Lusetti, Julia C Drees + Show 3 more

Open Access

https://doi.org/10.1074/jbc.m410371200

Copy DOI

Abstract

The DinI and RecX proteins of Escherichia coli both modulate the function of RecA protein, but have very different effects. DinI protein stabilizes RecA filaments, preventing disassembly but permitting assembly. RecX protein blocks RecA filament extension, which can lead to net filament disassembly. We demonstrate that both proteins can interact with the RecA filament, and propose that each can replace the other. The DinI/RecX displacement reactions are slow, requiring multiple minutes even when a large excess of the challenging protein is present. The effects of RecX protein on RecA filaments are manifest at lower modulator concentrations than the effects of DinI protein. Together, the DinI and RecX proteins constitute a new regulatory network. The two proteins compete directly as mainly positive (DinI) and negative (RecX) modulators of RecA function.

Highlights

RecA is the central recombination protein in Escherichia coli and other bacteria, playing an important role in the processes of recombinational DNA repair
Changes in ATP hydrolysis seen when directly as mainly positive (DinI) or RecX are added to RecA filaments reflect changes in the absolute amount of DNA-bound RecA protein as opposed to changes in the intrinsic ATPase activity of the filaments [15, 19]
When RecX (60 nM) is added instead of DinI, a slow decline in the ATP hydrolysis rate was measured as the RecA filaments disassembled

Summary

The DinI and RecX Proteins Are Competing Modulators of RecA Function*

The DinI and RecX proteins of Escherichia coli both modulate the function of RecA protein, but have very different effects. DinI protein stabilizes RecA filaments, preventing disassembly but permitting assembly. RecX protein blocks RecA filament extension, which can lead to net filament disassembly. RecA regulates the induction of the SOS response by facilitating the autocatalytic cleavage of the LexA repressor protein [3] In these important roles, RecA protein functions as a nucleoprotein filament. RecA filament assembly and disassembly must be directed in the cell to ensure that RecA activities initiate properly both temporally and spatially. One modulator of these dynamic processes is the SSB protein. We set out to determine the effects of the two proteins on RecA filaments when they are added together

EXPERIMENTAL PROCEDURES

RecA Regulation by DinI and RecX

RESULTS

DISCUSSION