title: Isolation, identification, and transcriptional specificity of the heat shock sigma factor sigma32 from Caulobacter crescentus.
abstract: We report the identification of the Caulobacter crescentus heat shock factor sigma32 as a 34-kDa protein that copurifies with the RNA polymerase holoenzyme. The N-terminal amino acid sequence of this protein was determined and used to design a degenerate oligonucleotide as a probe to identify the corresponding gene, rpoH, which encodes a predicted protein with a molecular mass of 33,659 Da. The amino acid sequence of this protein is similar to those of known bacterial heat shock sigma factors of Escherichia coli (41% identity), Pseudomonas aeruginosa (40% identity), and Citrobacter freundii (38% identity). The isolated C. crescentus gene complements the growth defect of an E. coli rpoH deletion strain at 37 degrees C, and Western blot (immunoblot) analysis confirmed that the gene product is related to the E. coli sigma32 protein. The purified RpoH protein in the presence of RNA polymerase core enzyme specifically recognizes the heat shock-regulated promoter P1 of the C. crescentus dnaK gene, and base pair substitutions in either the -10 or -35 region of this promoter abolish transcription. S1 nuclease mapping indicates that rpoH transcripts originate from two promoters, P1 and P2, under the normal growth conditions. The P2 promoter is similar to the sigma32 promoter consensus, and the P2-specific transcript increases dramatically during heat shock, while the P1-specific transcript remains relatively constant. These results suggest that although the structure and function of C. crescentus sigma32 appear to be very similar to those of its E. coli counterpart, the C. crescentus rpoH gene contains a novel promoter structure and may be positively autoregulated in response to environmental stress.
authors.affiliation: Lewis Thomas Laboratory, Department of Molecular Biology, Princeton University, Princeton, New Jersey 08544-1014, USA.
authors.forename: J
authors.initials: J
authors.lastname: Wu
authors.forename: A
authors.initials: A
authors.lastname: Newton
mesh_terms: D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D001483:Base Sequence; D001665:Binding Sites; D016935:Caulobacter crescentus / Q000235:genetics* / Q000378:metabolism; D015342:DNA Probes; D004269:DNA, Bacterial / Q000378:metabolism; D012321:DNA-Directed RNA Polymerases / Q000302:isolation & purification / Q000378:metabolism; D029968:Escherichia coli Proteins; D015964:Gene Expression Regulation, Bacterial; D018840:HSP70 Heat-Shock Proteins / Q000235:genetics; D006360:Heat-Shock Proteins / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D006358:Hot Temperature; D008969:Molecular Sequence Data; D017386:Sequence Homology, Amino Acid; D012808:Sigma Factor / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D014157:Transcription Factors; D014158:Transcription, Genetic
chemical_list: D001426:Bacterial Proteins; D015342:DNA Probes; D004269:DNA, Bacterial; D029968:Escherichia coli Proteins; D018840:HSP70 Heat-Shock Proteins; D006360:Heat-Shock Proteins; D012808:Sigma Factor; D014157:Transcription Factors; C069774:heat-shock sigma factor 32; D012321:DNA-Directed RNA Polymerases; C063842:dnaK protein, E coli