title: Novel heat shock protein HspQ stimulates the degradation of mutant DnaA protein in Escherichia coli.
abstract: Escherichia coli DnaA protein initiates chromosomal replication and is an important regulatory target during the replication cycle. In this study, a suppressor mutation isolated by transposon mutagenesis was found to allow growth of the temperature-sensitive dnaA508 and dnaA167 mutants at 40 degrees C. The suppressor consists of a transposon insertion in a previously annotated ORF, here termed hspQ, a novel heat shock gene whose promoter is recognized by the major heat shock sigma factor sigma32. Expression of hspQ on a pBR322 derivative inhibits growth of the dnaA508 and dnaA167 mutants at 30 degrees C, whereas growth of dnaA46 and other dnaA mutants is insensitive to changes in the level of hspQ. Cellular DnaA508 protein is degraded rapidly at elevated temperature, but hspQ disruption impedes this process. In contrast, DnaA46 protein is rapidly degraded in an hspQ-independent manner. Gel-filtration and chemical cross-linking experiments suggest that HspQ forms a stable homodimer in solution and can form homomultimers consisting of about four monomers. Heat-shock induced proteases such as Clp contain homomultimers of subunit proteins. We propose that HspQ is a new factor involved in the quality control of proteins and that it functions by excluding denatured proteins.
authors.affiliation: Department of Molecular Biology, Graduate School of Pharmaceutical Sciences, Kyushu University, 3-1-1 Maidashi, Higashi-ku, Fukuoka 812-8582, Japan.
authors.forename: Toh-ru
authors.initials: TR
authors.lastname: Shimuta
authors.forename: Kiyotaka
authors.initials: K
authors.lastname: Nakano
authors.forename: Yoko
authors.initials: Y
authors.lastname: Yamaguchi
authors.forename: Shogo
authors.initials: S
authors.lastname: Ozaki
authors.forename: Kazuyuki
authors.initials: K
authors.lastname: Fujimitsu
authors.forename: Chika
authors.initials: C
authors.lastname: Matsunaga
authors.forename: Kenji
authors.initials: K
authors.lastname: Noguchi
authors.forename: Akiko
authors.initials: A
authors.lastname: Emoto
authors.forename: Tsutomu
authors.initials: T
authors.lastname: Katayama
mesh_terms: D000483:Alleles; D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D001483:Base Sequence; D004261:DNA Replication; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D004926:Escherichia coli / Q000235:genetics*; D029968:Escherichia coli Proteins / Q000235:genetics* / Q000302:isolation & purification / Q000502:physiology*; D006360:Heat-Shock Proteins / Q000235:genetics* / Q000302:isolation & purification / Q000378:metabolism / Q000502:physiology*; D008969:Molecular Sequence Data; D009154:Mutation; D011489:Protein Denaturation; D015854:Up-Regulation
chemical_list: D001426:Bacterial Proteins; D004268:DNA-Binding Proteins; C066312:DnaA protein, Bacteria; D029968:Escherichia coli Proteins; D006360:Heat-Shock Proteins; C502771:HspQ protein, E coli