Northern hybridization and S1 nuclease mapping demonstrated that the groES and groEL genes in Pseudomonas aeruginosa were transcribed as a bicistronic mRNA of 2.2 kb. Two transcription start sites and a transcription termination site were mapped. Overlapping consensus sequences for sigma 32- and sigma 70-dependent promoters were found in the upstream region of groES. Levels of groESL-specific mRNA were increased about 2-fold upon heat shock. This response differs from the dramatic enhancement (more than 10-fold) of groESL transcription after heat shock observed in other bacterial species.