PMID:11850398

Citation	Chatterji, M and Nagaraja, V (2002) GyrI: a counter-defensive strategy against proteinaceous inhibitors of DNA gyrase. EMBO Rep. 3:261-7
Abstract	DNA gyrase is the target of two plasmid-encoded toxins CcdB and microcin B17, which ensure plasmid maintenance. These proteins stabilize gyrase-DNA covalent complexes leading to double-strand breaks in the genome. In contrast, the physiological role of chromosomally encoded inhibitor of DNA gyrase (GyrI) in Escherichia coli is unclear and its mechanism of inhibition has not been established. We demonstrate that the mode of inhibition of GyrI is distinct from all other gyrase inhibitors. It inhibits DNA gyrase prior to, or at the step of, binding of DNA by the enzyme. GyrI reduces intrinsic as well as toxin-stabilized gyrase-DNA covalent complexes. Furthermore, GyrI reduces microcin B17-mediated double-strand breaks in vivo, imparting protection to the cells against the toxin, substantiating the in vitro results. Thus, GyrI is an antidote to DNA gyrase-specific proteinaceous poisons encoded by plasmid addiction systems.
Links	PubMed PMC1084011 Online version:10.1093/embo-reports/kvf038
Keywords	Bacterial Proteins/genetics; Bacterial Proteins/physiology; Bacterial Toxins/genetics; Bacteriocins/genetics; Bacteriocins/pharmacology; DNA Gyrase/antagonists & inhibitors; Enzyme Inhibitors; Escherichia coli/enzymology; Escherichia coli/physiology; Escherichia coli Proteins; Plasmids; Repressor Proteins
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