title: Isolation and characterization of a dnaK genomic locus in a halotolerant cyanobacterium Aphanothece halophytica.
abstract: We cloned and characterized a genomic locus encoding a distinct member of the DnaK/Hsp70 family of molecular chaperones, dnaK1, from the halotolerant cyanobacterium Aphanothece halophytica. Co-expression of dnaK1 with a plant plastocyanin precursor in Escherichia coli resulted in a dramatic increase in the solubility of the plant protein. This indicates that A. halophytica dnaK1 encodes a functional protein possessing functions assigned to DnaK/Hsp70 chaperone members. The A. halophytica dnaK1 locus also encompasses grpE and dnaJ homologue genes in the order grpE-dnaK1-dnaJ. The transcript content of dnaK1 increased strongly upon subjecting cyanobacterial cells to heat stress. Northern analyses using specific probes indicated transcript species of 2.8, 2.2, 1.3, and 0.7 kb, which comprised grpE-dnaK1, dnaK1, dnaJ, and grpE, respectively. This indicates the presence of different terminators and/or heat stress promoters in this locus. Both dnaK1 transcript and protein levels increased in cyanobacterial cells transferred to hyperosmotic environments, suggesting a role of DnaK1 in the protection and/or recovery of A. halophytica from this particular stress.
authors.affiliation: BioScience Center, School of Agricultural Science, Nagoya University, Aichi, Japan.
authors.forename: B H
authors.initials: BH
authors.lastname: Lee
authors.forename: T
authors.initials: T
authors.lastname: Hibino
authors.forename: J
authors.initials: J
authors.lastname: Jo
authors.forename: A M
authors.initials: AM
authors.lastname: Viale
authors.forename: T
authors.initials: T
authors.lastname: Takabe
mesh_terms: D000595:Amino Acid Sequence; D001483:Base Sequence; D003001:Cloning, Molecular; D000458:Cyanobacteria / Q000235:genetics* / Q000502:physiology; D004926:Escherichia coli / Q000235:genetics; D029968:Escherichia coli Proteins; D015964:Gene Expression Regulation, Bacterial; D005798:Genes, Bacterial; D016680:Genome, Bacterial; D018840:HSP70 Heat-Shock Proteins / Q000096:biosynthesis / Q000737:chemistry / Q000235:genetics* / Q000302:isolation & purification*; D006358:Hot Temperature; D006982:Hypertonic Solutions; D008969:Molecular Sequence Data; D010802:Phylogeny; D011994:Recombinant Proteins / Q000096:biosynthesis; D012965:Sodium Chloride / Q000494:pharmacology
chemical_list: D029968:Escherichia coli Proteins; D018840:HSP70 Heat-Shock Proteins; D006982:Hypertonic Solutions; D011994:Recombinant Proteins; D012965:Sodium Chloride; C063842:dnaK protein, E coli