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The influence of DNA topology on the environmental regulation of a pH‐regulated locus in Salmonella typhimurium
Author(s) -
Karem Kevin,
Foster John W.
Publication year - 1993
Publication title -
molecular microbiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.857
H-Index - 247
eISSN - 1365-2958
pISSN - 0950-382X
DOI - 10.1111/j.1365-2958.1993.tb00905.x
Subject(s) - dna supercoil , biology , osmotic concentration , dna , repressor , gene , plasmid , operator (biology) , genetics , locus (genetics) , topology (electrical circuits) , operon , regulation of gene expression , transcription (linguistics) , gene expression , biophysics , microbiology and biotechnology , biochemistry , mutant , dna replication , mathematics , linguistics , philosophy , combinatorics
Summary Salmonella typhimurium is exposed to major shifts in H + concentration both in its natural and pathogenic environments. The organism undergoes extensive changes in gene expression in response to these pH fluctuations. A current question of regulatory biology is how a change in external pH selectively modulates transcription. We have analysed the expression of one such pH‐regulated locus, aniG , and found it is controlled by several additional environmental conditions including osmolarity and oxygen. For factors such as osmolarity and anaerobiosis, an environmentally triggered change in DNA supercoiling has been suggested as a means for controlling gene expression. Thus, environmentally induced changes in DNA topology were explored as a possible common means for establishing the multiple controls on aniG. The involvement of DNA supercoiling in the genetic response of S. typhimurium to external pH has not previously been defined. This report establishes that alkaline environments lower the linking number of reporter plasmids when compared to acidic environments. A consistent pattern was then established whereby conditions or mutations leading to either increased or decreased negative supercoiling were associated with altered expression of aniG. A similar relationship was observed for another environmentally regulated locus, proU. The DNA topology effects on aniG expression were dependent on the presence of EarA, the negative regulator of aniG. These data can be explained by a model in which repressor‐operator interactions are very sensitive to changes in operator conformation. These environmentally induced topological influences on operator DNA structure contribute to the magnitude of pH control exerted upon aniG.