title: Growth rate toxicity phenotypes and homeostatic supercoil control differentiate Escherichia coli from Salmonella enterica serovar Typhimurium.
abstract: Escherichia coli and Salmonella enterica serovar Typhimurium share high degrees of DNA and amino acid identity for 65% of the homologous genes shared by the two genomes. Yet, there are different phenotypes for null mutants in several genes that contribute to DNA condensation and nucleoid formation. The mutant R436-S form of the GyrB protein has a temperature-sensitive phenotype in Salmonella, showing disruption of supercoiling near the terminus and replicon failure at 42 degrees C. But this mutation in E. coli is lethal at the permissive temperature. A unifying hypothesis for why the same mutation in highly conserved homologous genes of different species leads to different physiologies focuses on homeotic supercoil control. During rapid growth in mid-log phase, E. coli generates 15% more negative supercoils in pBR322 DNA than Salmonella. Differences in compaction and torsional strain on chromosomal DNA explain a complex set of single-gene phenotypes and provide insight into how supercoiling may modulate epigenetic effects on chromosome structure and function and on prophage behavior in vivo.
authors.affiliation: Department of Biochemistry and Molecular Genetics, University of Alabama at Birmingham, Birmingham, AL 35294, USA.
authors.forename: Keith
authors.initials: K
authors.lastname: Champion
authors.forename: N Patrick
authors.initials: NP
authors.lastname: Higgins
mesh_terms: D001426:Bacterial Proteins / Q000032:analysis / Q000235:genetics; D027081:DNA Gyrase / Q000235:genetics* / Q000378:metabolism; D004278:DNA, Superhelical / Q000737:chemistry*; D004926:Escherichia coli / Q000235:genetics* / Q000254:growth & development; D010641:Phenotype; D010957:Plasmids / Q000235:genetics*; D012486:Salmonella typhimurium / Q000235:genetics* / Q000254:growth & development
chemical_list: D001426:Bacterial Proteins; D004278:DNA, Superhelical; D027081:DNA Gyrase