By EMSA we established that RprY binds to the promoter regions of groES, dnaK and clpB. We reasoned that Na + -depletion caused oxidation of metabolites and proteins, and induction of RprY. Parent cells mount a stress response that included activation of OxyR regulated genes, e.g. superoxide dismutase [25] and repression of RprY-regulated genes, e.g. ahpCF [9] as well as heat shock proteins and chaperones to protect cells from protein oxidation and misfolding. The transcription **data** suggests that RprY acts as a repressor of dnaK, groESL and clpB which may help the parent adapt to Na + stress. In the mutant lacking RprY, groESL, dnaK and clpB expression cannot be repressed which may contribute to the growth defect upon Na + -depletion. The expression of heat shock proteins is tightly controlled by both positive and negative regulation [36,37]. The expression of several of HSP chaperones is maintained at basal levels by mechanisms that include negative feedback loops [38] and blocking of promoters by CIRCE sequences and negative regulators [39]. Positive regulation is achieved by expression of alternate sigma factors [36]. Thus HSP expression is tightly coordinated with cell requirements during stress and non-stress conditions to ensure survival. Analysis of Porphyromonas gingivalis HSP promoter regions did not identify the classic CIRCE sequences required for negative regulation, leading to the assumption that Porphyromonas may utilize different control mechanisms.