HRCA, ENCODING THE REPRESSOR OF THE GROEL GENES IN STREPTOMYCES-ALBUS-G, IS ASSOCIATED WITH A 2ND DNAJ GENE

Expression of the principal chaperones of the heat shock stimulon of S treptomyces albus G are under the negative control of different repres sors. The dnaK operon is regulated by hspR, the last gene of the opero n (dnaK-grpE-dnaJ-hspR). hsp18, encoding a member of the small heat sh ock protein family, is regulated by orfY, which is in the opposite ori entation upstream of hsp18. The groES-groEL1 operon and the groEL2 gen e are regulated differently. They present tandem copies of the CIRCE e lement found in the 5' region of many heat shock genes and shown to ac t in Bacillus subtilis as an operator for a repressor encoded by hrcA (hrc stands for heat regulation at CIRCE). We report the identificatio n in S. albus of a new heat shock operon containing hrcA and dnaJ homo logs. Disruption of hrcA increased the transcription of the groES-groE L1 operon and of the groEL2 gene. These features were lost when the mu tant was complemented in trans by an intact copy of hrcA. Despite cons iderable accumulation of the GroE chaperones in the hrcA mutant, there was no effect on formation of the aerial mycelium and sporulation, in dicating that neither hrcA nor the level of groE gene expression is di rectly involved in the regulation of Streptomyces morphological differ entiation.