Suppression of temperature-sensitivity of a dnaA46 mutant by excessive DNA supercoiling

摘要

pWe report here that the high-temperature sensitivity of a idnaA46/i mutant was suppressed by addition of high concentrations of NaCl into the culture medium. This suppression was also observed with other high-temperature-sensitive idnaA/i mutants, except idnaA167/i and idnaA508/i mutants, which have mutations in the N-terminal region of DnaA protein. Since high concentrations of NaCl in the medium increased negative DNA supercoiling in a idnaA46/i mutant, we hypothesized that the increase in DNA supercoiling is involved in the suppression of the temperature-sensitivity of the idnaA46/i mutant by high concentrations of NaCl. This hypothesis was supported by iin vitro/i and iin vivo/i results as follows. A low DNA replication activity of purified DnaA46 protein at high temperatures was increased in line with an increase in DNA supercoiling of template DNA. The idnaA46/i mutant showed higher sensitivity to nalidixic acid, a DNA-relaxing drug, than did the wild-type cells under the conditions of high temperatures and high concentrations of NaCl./p