RT Journal Article SR Electronic(1) A1 Oke, Valerie A1 Rushing, Brenda G A1 Fisher, Emily J A1 Moghadam-Tabrizi, Mohamad A1 Long, Sharon RYR 2001 T1 Identification of the heat-shock sigma factor RpoH and a second RpoH-like protein in Sinorhizobium melilotiThe GenBank accession numbers for the sequences reported in this paper are AF128845 (rpoH1) and AF149031 (rpoH2). JF Microbiology, VO 147 IS 9 SP 2399 OP 2408 DO https://doi.org/10.1099/00221287-147-9-2399 PB Microbiology Society, SN 1465-2080, AB 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 σ32 (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 °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., UL https://www.microbiologyresearch.org/content/journal/micro/10.1099/00221287-147-9-2399