title: Suppression of chromosome segregation defects of Escherichia coli muk mutants by mutations in topoisomerase I.
abstract: Escherichia coli muk mutants are temperature-sensitive and produce anucleate cells. A spontaneously occurring mutation was found in a DeltamukBkan mutant strain that suppressed the temperature-sensitive phenotype and mapped in or near topA, the gene that encodes topoisomerase I. Previously characterized topA mutations, topA10 and topA66, were found to be general suppressors of muk mutants: they suppressed temperature sensitivity and anucleate cell production of cells containing null or point mutations in mukB and null mutations in mukE or mukF. The suppression correlated with excess negative supercoiling by DNA gyrase, and the gyrase inhibitor, coumermycin, reversed it. Defects in topA allow 99% of cell division events in muk null mutants to proceed without chromosome loss or loss of cell viability. This observation imposes important limitations on models for Muk activity and is consistent with a role for MukBEF in chromosome folding and DNA condensation.
authors.affiliation: Advanced BioScience Laboratories Basic Research Program, National Cancer Institute, Frederick Cancer Research and Development Center, Frederick, MD 21702-1201, USA.
authors.forename: J A
authors.initials: JA
authors.lastname: Sawitzke
authors.forename: S
authors.initials: S
authors.lastname: Austin
mesh_terms: D049933:Aminocoumarins; D001426:Bacterial Proteins / Q000235:genetics; D002455:Cell Division / Q000235:genetics; D002470:Cell Survival / Q000235:genetics; D002868:Chromosomal Proteins, Non-Histone; D002869:Chromosome Aberrations; D003374:Coumarins / Q000494:pharmacology; D004264:DNA Topoisomerases, Type I / Q000235:genetics*; D004250:DNA Topoisomerases, Type II / Q000378:metabolism; D004278:DNA, Superhelical / Q000235:genetics; D004791:Enzyme Inhibitors / Q000494:pharmacology; D004926:Escherichia coli / Q000201:enzymology* / Q000235:genetics; D029968:Escherichia coli Proteins; D006651:Histocytochemistry; D009154:Mutation; D012097:Repressor Proteins; D013489:Suppression, Genetic; D013696:Temperature
chemical_list: D049933:Aminocoumarins; D001426:Bacterial Proteins; D002868:Chromosomal Proteins, Non-Histone; D003374:Coumarins; D004278:DNA, Superhelical; D004791:Enzyme Inhibitors; D029968:Escherichia coli Proteins; C067035:MukB protein, E coli; D012097:Repressor Proteins; C087115:mukE protein, E coli; C087116:mukF protein, E coli; D004264:DNA Topoisomerases, Type I; D004250:DNA Topoisomerases, Type II; C004628:coumermycin