Affiliation:
1. Department of Biology and Rosenstiel Basic Medical Sciences Research Center, Brandeis University, Waltham, Massachusetts 02454-9110
Abstract
ABSTRACT
RadA/Sms is a highly conserved eubacterial protein that shares sequence similarity with both RecA strand transferase and Lon protease. We examined mutations in the
radA/sms
gene of
Escherichia coli
for effects on conjugational recombination and sensitivity to DNA-damaging agents, including UV irradiation, methyl methanesulfonate (MMS), mitomycin C, phleomycin, hydrogen peroxide, and hydroxyurea (HU). Null mutants of
radA
were modestly sensitive to the DNA-methylating agent MMS and to the DNA strand breakage agent phleomycin, with conjugational recombination decreased two- to threefold. We combined a
radA
mutation with other mutations in recombination genes, including
recA
,
recB
,
recG
,
recJ
,
recQ
,
ruvA
, and
ruvC
. A
radA
mutation was strongly synergistic with the
recG
Holliday junction helicase mutation, producing profound sensitivity to all DNA-damaging agents tested. Lesser synergy was noted between a mutation in
radA
and
recJ
,
recQ
,
ruvA
,
ruvC
, and
recA
for sensitivity to various genotoxins. For survival after peroxide and HU exposure, a
radA
mutation surprisingly suppressed the sensitivity of
recA
and
recB
mutants, suggesting that RadA may convert some forms of damage into lethal intermediates in the absence of these functions. Loss of
radA
enhanced the conjugational recombination deficiency conferred by mutations in Holliday junction-processing function genes,
recG
,
ruvA
, and
ruvC
. A
radA recG ruv
triple mutant had severe recombinational defects, to the low level exhibited by
recA
mutants. These results establish a role for RadA/Sms in recombination and recombinational repair, most likely involving the stabilization or processing of branched DNA molecules or blocked replication forks because of its genetic redundancy with RecG and RuvABC.
Publisher
American Society for Microbiology
Subject
Molecular Biology,Microbiology
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