Identification of the heat-shock sigma factor RpoH and a second RpoH-like protein in Sinorhizobium meliloti

Microbiology (Reading). 2001 Sep;147(Pt 9):2399-2408. doi: 10.1099/00221287-147-9-2399.


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.

Publication types

  • Research Support, U.S. Gov't, Non-P.H.S.
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Bacterial Proteins / genetics*
  • Chromosome Mapping
  • DNA, Bacterial / genetics
  • DNA, Bacterial / isolation & purification
  • Escherichia coli / genetics
  • Genes, Bacterial
  • Heat-Shock Proteins / genetics*
  • Molecular Sequence Data
  • Mutagenesis, Insertional
  • Mutation
  • Plasmids / genetics
  • Recombinant Fusion Proteins / genetics
  • Sigma Factor / genetics*
  • Sinorhizobium meliloti / genetics*
  • Transcription Factors / genetics*


  • Bacterial Proteins
  • DNA, Bacterial
  • Heat-Shock Proteins
  • Recombinant Fusion Proteins
  • Sigma Factor
  • Transcription Factors
  • heat-shock sigma factor 32

Associated data

  • GENBANK/AF128845
  • GENBANK/AF149031