RheA, the repressor of hsp18 in Streptomyces albus G.

In Streptomyces albus, Hsp18, a protein belonging to the family of small heat-shock proteins, can be detected only at high temperature. Disruption of orfY, located upstream and in the opposite orientation to hsp18, resulted in an elevated level of hsp18 mRNA at low temperature. Genetic and biochemical experiments indicated that the product of orfY, now called RheA (Repressor of hsp eighteen), directly represses hsp18. In Escherichia coli, an hsp18'-bgaB transcriptional fusion was repressed in a strain expressing S. albus RheA. DNA-binding experiments with crude extracts of E. coli overproducing RheA indicated that RheA interacts specifically with the hsp18 promoter. Transcription analysis of rheA in the S. albus wild-type and in rheA mutant strains suggested that RheA represses transcription not only of hsp18 but also of rheA itself.