Identification of the heat-shock sigma factor RpoH and a second RpoH-like protein in Sinorhizobium meliloti.
Hybridization to a PCR product derived from conserved sigma-factor sequences led to the identification of two Sinorhizobium meliloti DNA segments that display significant sequence similarity to the family of rpoH genes encoding the sigma(32) (RpoH) heat-shock transcription factors. The first gene, rpoH1, complements an Escherichia coli rpoH mutation. Cells containing an rpoH1 mutation are impaired in growth at 37 degrees C under free-living conditions and are defective in nitrogen fixation during symbiosis with alfalfa. A plasmid-borne rpoH1-gusA fusion increases in expression upon entry of the culture into the stationary phase of growth. The second gene, designated rpoH2, is 42% identical to the S. meliloti rpoH1 gene. Cells containing an rpoH2 mutation have no apparent phenotype under free-living conditions or during symbiosis with the host plant alfalfa. An rpoH2-gusA fusion increases in expression during the stationary phase of growth. The presence of two rpoH-like sequences in S. meliloti is reminiscent of the situation in Bradyrhizobium japonicum, which has three rpoH genes.
Oke
Valerie
V
Department of Biological Sciences, A527A Langley Hall, University of Pittsburgh, Pittsburgh, PA 15260, USA3.|Department of Biological Sciences1 and Howard Hughes Medical Institute2, Stanford University, Stanford, CA 94305, USA.
Rushing
Brenda G
BG
Department of Biological Sciences1 and Howard Hughes Medical Institute2, Stanford University, Stanford, CA 94305, USA.
Fisher
Emily J
EJ
Department of Biological Sciences, A527A Langley Hall, University of Pittsburgh, Pittsburgh, PA 15260, USA3.
Moghadam-Tabrizi
Mohamad
M
Department of Biological Sciences1 and Howard Hughes Medical Institute2, Stanford University, Stanford, CA 94305, USA.
Long
Sharon R
SR
Department of Biological Sciences1 and Howard Hughes Medical Institute2, Stanford University, Stanford, CA 94305, USA.
D001426:Bacterial Proteins / Q000235:genetics*; D002874:Chromosome Mapping; D004269:DNA, Bacterial / Q000235:genetics / Q000302:isolation & purification; D004926:Escherichia coli / Q000235:genetics; D005798:Genes, Bacterial; D006360:Heat-Shock Proteins / Q000235:genetics*; D008969:Molecular Sequence Data; D016254:Mutagenesis, Insertional; D009154:Mutation; D010957:Plasmids / Q000235:genetics; D011993:Recombinant Fusion Proteins / Q000235:genetics; D012808:Sigma Factor / Q000235:genetics*; D016962:Sinorhizobium meliloti / Q000235:genetics*; D014157:Transcription Factors / Q000235:genetics*
D001426:Bacterial Proteins; D004269:DNA, Bacterial; D006360:Heat-Shock Proteins; D011993:Recombinant Fusion Proteins; D012808:Sigma Factor; D014157:Transcription Factors; C069774:heat-shock sigma factor 32