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Mutations in topA interfere with the inducible expression of DNA damage response loci in salmonella typhimurium
Author(s) -
Smith C. Mark,
Arany Zoltan,
Orrego Cristian,
Eisenstadt Eric
Publication year - 1992
Publication title -
environmental and molecular mutagenesis
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1
H-Index - 87
eISSN - 1098-2280
pISSN - 0893-6692
DOI - 10.1002/em.2850190302
Subject(s) - repressor lexa , dna supercoil , biology , operon , dna gyrase , dna , sos response , escherichia coli , nucleoid , dna damage , rpos , bacteria , microbiology and biotechnology , dna repair , genetics , repressor , gene , gene expression , dna replication , promoter
Abstract Strains of Salmonella typhimurium deficient in topoisomerase I activity ( topA mutants) are UV sensitive and non‐mutable (Overbye and Margolin: J Bacteriol 146:170–178, 1981). Using lac‐operon fusions to DNA damage inducible (din) loci we investigated whether these observations could be explained by an inability of topA strains to efficiently induce DNA damage responses. Mitomycin C (MMC)‐induced expression of lac‐operon fusions to uvrB and to a second SOS locus, din ‐9, was largely eliminated in topA bacteria. The inducible expression of several other din ‐fusions was also diminished. This inducibility defect was mimicked by growth of din ‐9 topA + bacteria in media of high osmolarity, a condition that leads to increased DNA supercoiling. Inhibitors of DNA gyrase efficiently induced din ‐9 in topA bacteria. Together, these results suggest that the topA effect on din expression may be mediated at the level of DNA supercoiling. The sensitivities of a number of din ‐fusions to topA paralleled the degree to which they were repressed by excess LexA, suggesting that mutations in topA might influence LexA‐operator interactions and/or increase lexA expression.