title: The effect of the rpoSam allele on gene expression and stress resistance in Escherichia coli.
abstract: The RNA polymerase associated with RpoS transcribes many genes related to stationary phase and stress survival in Escherichia coli. The DNA sequence of rpoS exhibits a high degree of polymorphism. A C to T transition at position 99 of the rpoS ORF, which results in a premature amber stop codon often found in E. coli strains. The rpoSam mutant expresses a truncated and partially functional RpoS protein. Here, we present new evidence regarding rpoS polymorphism in common laboratory E. coli strains. One out of the six tested strains carries the rpoSam allele, but expressed a full-length RpoS protein owing to the presence of an amber supressor mutation. The rpoSam allele was transferred to a non-suppressor background and tested for RpoS level, stress resistance and for the expression of RpoS and sigma70-dependent genes. Overall, the rpoSam strain displayed an intermediate phenotype regarding stress resistance and the expression of σ(S)-dependent genes when compared to the wild-type rpoS(+) strain and to the rpoS null mutant. Surprisingly, overexpression of rpoSam had a differential effect on the expression of the σ(70)-dependent genes phoA and lacZ that, respectively, encode the enzymes alkaline phosphatase and β-galactosidase. The former was enhanced while the latter was inhibited by high levels of RpoSam.
authors.affiliation: Departamento de Microbiologia, Instituto de Ciências Biomédicas, Universidade de São Paulo, Av. Prof. Lineu Prestes, 1374, São Paulo, SP, CEP: 05508-900, Brazil.
authors.forename: Heloisa F
authors.initials: HF
authors.lastname: Galbiati
authors.forename: Natalia P
authors.initials: NP
authors.lastname: Taschner
authors.forename: Beny
authors.initials: B
authors.lastname: Spira
mesh_terms: D000469:Alkaline Phosphatase / Q000378:metabolism; D000483:Alleles; D001426:Bacterial Proteins / Q000235:genetics* / Q000378:metabolism; D001483:Base Sequence; D018389:Codon, Nonsense; D048168:Escherichia coli K12 / Q000235:genetics* / Q000502:physiology; D015870:Gene Expression; D015964:Gene Expression Regulation, Bacterial; D005798:Genes, Bacterial; D050296:Microbial Viability; D010641:Phenotype; D055049:Salt Tolerance; D012808:Sigma Factor / Q000235:genetics* / Q000378:metabolism; D013312:Stress, Physiological; D001616:beta-Galactosidase / Q000235:genetics / Q000378:metabolism
chemical_list: D001426:Bacterial Proteins; D018389:Codon, Nonsense; D012808:Sigma Factor; C069567:sigma factor KatF protein, Bacteria; D000469:Alkaline Phosphatase; D001616:beta-Galactosidase