Disruption of hspR, the repressor gene of the dnaK operon in Streptomyces albus G

hspR is the distal gene of the Streptomyces albus dnaK operon. It encodes a protein similar to GlnR, the repressor of the Bacillus subtilis glutamine synthetase gene. Transcriptional analysis showed that disruption of hspR led to constitutive high-level expression of the dnaK operon. SDS-PAGE analysis revealed overproduction and accumulation of the chaperone DnaK at low temperature. HSP94, a heat-inducible protein cross-reacting with anti-ClpB antibodies, was also shown to be constitutively overexpressed at low temperature in the hspR mutant. Those features were lost when the mutant was complemented in trans by an intact copy of hspR. The hspR mutant was impaired in its growth on solid rich medium: colonies grow slowly at 30 degrees C. However, formation of aerial mycelium and sporulation was not prevented. In liquid culture growth curves of the mutant and the wild type were similar. The kinetics of groEL gene induction were not modified by the hspR null mutation, indicating that HspR was not directly involved in the control of groEL transcription. Thus, in contrast with B. subtilis and other Gram-positive bacteria, transcription of Streptomyces dnaK and groEL operons is not controlled by the same regulator.