title: Differential protease-mediated turnover of H-NS and StpA revealed by a mutation altering protein stability and stationary-phase survival of Escherichia coli.
abstract: The Escherichia coli proteins H-NS is recognized as an important component among the major nucleoid-associated proteins. In studies of E. coli strains with defects in H-NS, we discovered a mutant that phenotypically restored stationary-phase viability (Rsv) of such strains. The Rsv phenotype was the result of a mutation that led to severalfold higher levels of the functionally and structurally related StpA protein. This mutation was a base pair change in the stpA structural gene, and the amino acid substitution in the StpA protein altered its turnover properties, suggesting a role for this residue in a cleavage site for proteolysis. We determined the stability of the StpA and the H-NS proteins and found that the StpA protein was degraded relatively rapidly in strains lacking functional H-NS, whereas H-NS remained stable irrespective of the presence/absence of StpA. Using protease-deficient mutants, we obtained evidence that the Lon protease was responsible for the degradation of StpA. The differential turnover of the nucleoid-associated proteins is suggested to contribute to the regulation of their stoichiometry and ratio in terms of homo- and heteromer formation. We conclude that StpA, in contrast to H-NS, is present mainly in heteromeric form in E. coli.
authors.affiliation: Department of Microbiology, Umeâ University, S-90187 Umeâ, Sweden.
authors.forename: J
authors.initials: J
authors.lastname: Johansson
authors.forename: B E
authors.initials: BE
authors.lastname: Uhlin
mesh_terms: D049069:ATP-Dependent Proteases; D000595:Amino Acid Sequence; D001426:Bacterial Proteins; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D004926:Escherichia coli / Q000235:genetics*; D029968:Escherichia coli Proteins; D005838:Genotype; D006360:Heat-Shock Proteins / Q000378:metabolism*; D008954:Models, Biological; D018832:Molecular Chaperones; D008969:Molecular Sequence Data; D009154:Mutation; D010641:Phenotype; D017354:Point Mutation; D049070:Protease La; D012697:Serine Endopeptidases / Q000378:metabolism*; D013997:Time Factors
chemical_list: D001426:Bacterial Proteins; D004268:DNA-Binding Proteins; D029968:Escherichia coli Proteins; C031908:H-NS protein, bacteria; D006360:Heat-Shock Proteins; D018832:Molecular Chaperones; C090104:StpA protein, E coli; D049069:ATP-Dependent Proteases; D012697:Serine Endopeptidases; C483567:Lon protein, E coli; D049070:Protease La