title: Relaxation of transcription-induced negative supercoiling is an essential function of Escherichia coli DNA topoisomerase I.
abstract: It has been suggested that the essential function of DNA topoisomerase I in Escherichia coli is to prevent chromosomal DNA from reaching an unacceptably high level of global negative supercoiling. However, other in vivo studies have shown that DNA topoisomerase I is very effective in removing local negative supercoiling generated during transcription elongation. To determine whether topoisomerase I is essential for controlling global or local DNA supercoiling, we have prepared a set of topA null mutant strains in combination with different plasmid DNAs. Although we found a correlation between the severity of the growth defect with both transcription-induced and global supercoiling, near to complete growth inhibition correlated only with transcription-induced supercoiling. This result strongly suggests that the major function of DNA topoisomerase I is to relax local negative supercoiling generated during transcription elongation.
authors.affiliation: Département de Microbiologie et immunologie, Université de Montréal, C.P. 6128, Succursale Centre-Ville, Montréal, Québec, Canada H3C 3J7.
authors.forename: E
authors.initials: E
authors.lastname: Massé
authors.forename: M
authors.initials: M
authors.lastname: Drolet
mesh_terms: D017920:Antiporters / Q000235:genetics / Q000378:metabolism; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism; D004264:DNA Topoisomerases, Type I / Q000378:metabolism*; D004269:DNA, Bacterial / Q000737:chemistry / Q000378:metabolism; D004926:Escherichia coli / Q000201:enzymology* / Q000235:genetics / Q000254:growth & development; D009690:Nucleic Acid Conformation; D011401:Promoter Regions, Genetic; D013753:Tetracycline Resistance / Q000235:genetics; D014158:Transcription, Genetic
chemical_list: D017920:Antiporters; D001426:Bacterial Proteins; D004269:DNA, Bacterial; C079051:tetA protein, Bacteria; D004264:DNA Topoisomerases, Type I