Thermally induced expression of the heat-shock gene groEL is subject to post-transcriptional regulation in Streptomyces albus. When S. albus cells were shifted from 30 degrees C to 41 degrees C, synthesis of three GroEL-like proteins was induced from two genes transcribed from associated promoters P1 and P2. Surprisingly, analyses of transcriptional fusions of these promoters with various reporter genes indicated constitutive expression independent of heat shock. In contrast, neo expression was thermally inducible as a GroEL1-APH translational fusion protein. Furthermore, expression of the groEL1-neo gene was heat inducible even after the groEL1 promoter region was replaced by a heterologous non-heat-inducible promoter such as the Escherichia coli lac promoter. Finally, synthesis of GroE proteins, as well as the GroEL-APH fusion protein, was heat inducible when their transcription was inhibited by rifampicin. Post-transcriptional regulatory signals needed for heat-induced GroEL1 synthesis were mapped within of the groEL1 structural gene.