A 31 base pair synthetic oligonucleotide based on the genes for the Escherichia coli heat shock sigma factor (rpoH) and the Pseudomonas aeruginosa housekeeping sigma factor (rpoD) was employed in conjunction with the Tanaka et al. (K. Tanaka, T. Shiina, and H. Takahashi, 1988. Science (Washington, D.C.), 242: 1040-1042) RpoD box probe to identify the location of the rpoH gene in P. aeruginosa genomic digests. This gene was cloned into plasmid pGEM3Z(f+), sequenced, and found to share 67% nucleotide identity and 77% amino acid homology with the rpoH gene and its product (sigma 32) of E. coli. The plasmid containing the rpoH gene complemented the function of sigma 32 in an E. coli rpoH deletion mutant. Furthermore, this plasmid directed the synthesis of a 32-kDa protein in an E. coli S-30 in vitro transcription-translation system. Primer extension studies were used to identify the transcriptional start sites under control and heat-stressed (45 and 50 degrees C) conditions. Two promoter sites were identified having sequence homology to the E. coli sigma 70 and sigma 24 consensus sequences.