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Characterization of RecA1332 in vivo and in vitro . A role for α‐helix E as a liaison between the subunit–subunit interface and the DNA and ATP binding domains of RecA protein
Author(s) -
Bianco Piero R.,
Weinstock George M.
Publication year - 1998
Publication title -
genes to cells
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.912
H-Index - 115
eISSN - 1365-2443
pISSN - 1356-9597
DOI - 10.1046/j.1365-2443.1998.00168.x
Subject(s) - biology , protein subunit , cooperativity , atp hydrolysis , dna , biochemistry , mutant , cooperative binding , microbiology and biotechnology , homologous recombination , atpase , binding site , enzyme , gene
Background: The RecA protein of Escherichia coli is essential for homologous recombination and induction of the SOS response. RecA has three cysteines located at positions 90, 116 and 129. Chemical modification of these residues abolishes ATP hydrolysis and repressor cleavage, and causes a reduction in the DNA strand exchange and DNA strand annealing activities. Several mutants at each of these positions were isolated and partially characterized. One of these, recA1332 , replaces cysteine 129 with methionine. Although this is a relatively conservative mutation based on hydrophobicity, recA1332 was completely defective for DNA repair but the purified protein was active for ATPase in vitro . Results: In vivo , strains containing this mutant allele were shown to be defective when assayed for all RecA‐dependent activities. In vitro , RecA1332 protein possessed DNA‐dependent ATP hydrolysis activity that showed an increased sensitivity to inhibition by monovalent cations, and whose k cat was reduced 3‐ to 12‐fold. In addition, RecA1332 was unable to use oligodeoxyribonulceotides as ssDNA cofactors in the ATPase reaction. RecA1332 showed altered binding to single‐ and double‐stranded DNA and, although it was able to perform DNA strand exchange, it was slowed in its ability to both form joint molecule intermediates and to convert these species to product. Conclusions: Our results are consistent with a defect in intermolecular interactions between RecA monomers. We propose that α‐helix E (which includes C129M) is a liaison that connects the subunit–subunit interactions to DNA and ATP binding, thereby creating filament stability and cooperativity.