Regulation of DNA superhelicity by rpoB mutations that suppress defective Rho-mediated transcription termination in Escherichia coli.
AUTOR(ES)
Arnold, G F
RESUMO
The highly defective rho-15 mutant of Escherichia coli produces plasmid DNA that is 22% less negatively supercoiled than DNA from an isogenic wild-type strain (J. S. Fassler, G. F. Arnold, and I. Tessman, Mol. Gen. Genet. 204:424-429, 1986). We extended our measurements of plasmid superhelicity to additional rho mutants and to strains containing mutations that suppress rho transcription termination defects; the suppressor mutations were in the rpoB and the rho genes. The superhelicity of plasmid DNA was reduced by 11 and 10%, respectively, in the rho-702 and rho-201 mutants, both of which are less defective in Rho-mediated transcription termination than rho-15. Plasmid superhelicity was restored in all the suppressed rho mutants; in one rpoB mutant, plasmid DNA was even more negatively supercoiled than in rpoB+ cells, whether in a rho+ or rho mutant background. Suppression of rho mutants enabled them to maintain plasmids that could not be maintained in the mutants in the absence of the suppressor mutations. The results indicate that in addition to DNA gyrase, topoisomerase I, and Rho, RNA polymerase is also a determinant of DNA superhelicity, and its effect is modified by the Rho protein. We propose that Rho may increase the degree of DNA unwinding by the transcription complex, possibly at transcription termination sites.
ACESSO AO ARTIGO
http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=211436Documentos Relacionados
- Rifampin and rpoB mutations can alter DNA supercoiling in Escherichia coli.
- The attenuator of the tryptophan operon in E.coli: rho-mediated release of RNA polymerase from a transcription termination complex in vitro.
- Effect of dnaA and rpoB mutations on attenuation in the trp operon of Escherichia coli.
- Suppression of the DnaA phenotype by mutations in the rpoB cistron of ribonucleic acid polymerase in Salmonella typhimurium and Escherichia coli.
- Characterization of the pleiotropic phenotypes of rifampin-resistant rpoB mutants of Escherichia coli.