It was shown that the chaperonin GroEL/GroES and protease Lon influence the expression of the Vibrio fischeri lux regulon in Escherichia coli cells: E. coli groE mutants bearing hybrid plasmid with the lux regulon were weakly luminescent; cells of the E. coli lon- comprising the entire lux regulon display very intense bioluminescence, with no lag period in the induction curve characteristic of lon+ strains. The luxR gene was cloned from the Vibrio fischeri genome in the pGEX-KG vector. It was shown that the active fusion protein GST-LuxR by affinity chromatography on glutathione-sucrose colony is purified only with proteins GroEL and Lon. The present results showed that the LuxR, transcriptional activator of the V. fischeri lux operon, really complexes with GroEL chaperonin and Lon protease. We suppose, that the GroEL/GroES chaperonin systems is required for the folding of LuxR into an active protein, and the LuxR is the target for the ATP-dependent serine Lon protease of E. coli.