title: Identification of a turnover element in region 2.1 of Escherichia coli sigma32 by a bacterial one-hybrid approach.
abstract: Induction of the heat shock response in Escherichia coli requires the alternative sigma factor sigma32 (RpoH). The cellular concentration of sigma32 is controlled by proteolysis involving FtsH, other proteases, and the DnaKJ chaperone system. To identify individual sigma32 residues critical for degradation, we used a recently developed bacterial one-hybrid system and screened for stabilized versions of sigma32. The five single point mutations that rendered the sigma factor more stable mapped to positions L47, A50, and I54 in region 2.1. Strains expressing the stabilized sigma32 variants exhibited elevated transcriptional activity, as determined by a groE-lacZ fusion. Structure calculations predicted that the three mutated residues line up on the same face of an alpha-helix in region 2.1, suggesting that they are positioned to interact with proteins of the degradation machinery.
authors.affiliation: Institut für Mikrobiologie, Eidgenössische Technische Hochschule, Zürich, Switzerland.
authors.forename: Markus
authors.initials: M
authors.lastname: Obrist
authors.forename: Franz
authors.initials: F
authors.lastname: Narberhaus
mesh_terms: D000595:Amino Acid Sequence; D004926:Escherichia coli / Q000235:genetics* / Q000378:metabolism*; D005820:Genetic Testing; D006360:Heat-Shock Proteins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism*; D007763:Lac Operon; D008969:Molecular Sequence Data; D016296:Mutagenesis; D010641:Phenotype; D017433:Protein Structure, Secondary; D018085:Regulon / Q000502:physiology*; D012808:Sigma Factor / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism*; D020798:Two-Hybrid System Techniques
chemical_list: D006360:Heat-Shock Proteins; D012808:Sigma Factor; C069774:heat-shock sigma factor 32