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Escherichia coli tyrT gene transcription is sensitive to DNA supercoiling in its native chromosomal context: effect of DNA topoisomerase IV overexpression on tyrT promoter function
Author(s) -
Free Andrew,
Dorman Charles J.
Publication year - 1994
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.1365-2958.1994.tb01275.x
Subject(s) - dna supercoil , biology , topoisomerase , microbiology and biotechnology , transcription (linguistics) , dna , gene , dna gyrase , promoter , escherichia coli , plasmid , genetics , gene expression , dna replication , linguistics , philosophy
Summary We have investigated the in vivo DNA supercoiling sensitivity of the Escherichia coli tRNA tyr 1 gene ( tyrT ) promoter in its normal chromosomal location. Here, the native tyrT promoter is found to be exquisitely sensitive to mutations and to drugs which alter the level of DNA supercoiling. We show that the response of the tyrT promoter to supercoiling is qualitatively similar to that of a known supercoiling‐sensitive tRNA gene promoter, hisR. Specifically, treatments which increase in vivo DNA supercoiling levels enhance transcription of these tRNA genes. Particularly striking is the strong enhancement of expression from both promoters by a transposon insertion mutation in the topA gene encoding DNA topoisomerase i. This phenotypic effect can be complemented by providing active topoisomerase I in trans from a recombinant plasmid. Interestingly, it can also be complemented by overexpression of the genes encoding the subunits of DNA topoisomerase IV. We believe that this is the first demonstration that DNA topoisomerase IV can influence gene expression and it suggests that DNA topoisomerase I is partially redundant, at least in E. coli.