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Effect of the deletion of the σ 32 ‐dependent promoter (P1) of the Escherichia coli topoisomerase I gene on thermotolerance
Author(s) -
Qi Haiyan,
Menzel Rolf,
TseDinh YukChing
Publication year - 1996
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 - 10.1046/j.1365-2958.1996.241390.x
Subject(s) - biology , mutant , escherichia coli , dna gyrase , topoisomerase , microbiology and biotechnology , dna supercoil , plasmid , wild type , heat shock protein , dna , promoter , gene , heat shock , genetics , dna replication , gene expression
Topoisomerase I and DNA gyrase are the major topoisomerase activities responsible for the regulation of DNA supercoiling in the bacterium Escherichia coli . The P1 promoter of topA has previously been shown to be a σ 32 ‐dependent heat‐shock promoter. A mutant strain with a deletion of P1 was constructed. This mutant is >10‐fold more sensitive to heat treatment (52°C) than the wild type. After brief treatment at 42°C, wild‐type Escherichia coli acquires an enhanced resistance to the effects of a subsequent 52°C treatment. This is not the case for the P1 deletion mutant, which, and under these conditions, is about 100‐fold less thermotolerant than the wild type. The presence of a plasmid expressing topoisomerase I restored the heat‐survival level of the mutant to that of the wild type. During heat shock, the superhelical density of a plasmid with the heat‐inducible rpoD promoter is increased in the P1 deletion mutant. We also note that the pulse‐labelling pattern of proteins at 42°C (displayed on SDS–polyacrylamide gels) is different in the mutant, and, most notably, the amounts of DnaK and of GroEL protein are reduced. A model is proposed in order to unify these observations.