DNA supercoiling in a thermotolerant mutant of Escherichia coli

S. Marvin Friedman, Muhammad Malik, Karl Drlica

Research output: Contribution to journalArticlepeer-review

23 Scopus citations


A spontaneously occurring, nalidixic acid-resistant (NalR), thermotolerant (T/r) mutant of Escherichia coli was isolated. Bacteriophage P1-mediated transduction showed that NalR mapped at or near gyr A, one of the two genes encoding DNA gyrase. Expression of gyrA+ from a plasmid rendered the mutant sensitive to nalidixic acid and to high temperature, the result expected for alleles mapping in gyrA. Plasmid linking number measurements, made with DNA from cells grown at 37° C or shifted to 48° C, revealed that supercoiling was about 12% less negative in the T/r mutant than in the parental strain. Each strain preferentially expressed two different proteins at 48° C. The genetic and supercoiling data indicate that thermo-tolerance can arise from an alteration in DNA gyrase that lowers supercoiling. This eubacterial study, when. coupled with those of archaebacteria, suggests that DNA relaxation is a general aspect of thermotolerance.

Original languageEnglish (US)
Pages (from-to)417-422
Number of pages6
JournalMGG Molecular & General Genetics
Issue number4
StatePublished - Aug 1995
Externally publishedYes

ASJC Scopus subject areas

  • Genetics


  • DNA gyrase
  • DNA supercoiling
  • Escherichia coli
  • Nalidixic acid
  • Thermotolearnt mutant


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