Suppression of ftsH mutant phenotypes by overproduction of molecular chaperones.

Decreased intracellular levels of FtsH, a membrane-bound ATPase, led to retardation of growth and protein export, as well as to an abnormal translocation of alkaline phosphatase that had been attached to a cytoplasmic domain of a multispanning membrane protein, SecY. The last phenotype is designated Std (stop transfer defective). In this study, we examined the effects of overproduction of some molecular chaperones on the phenotypes of ftsH mutants. The growth retardation was partially suppressed by overproduction of GroEL/GroES (Hsp60/Hsp10) or HtpG (Hsp90), although these chaperones could not totally substitute for FtsH. Overproduction of HtpG specifically alleviated the Std phenotype, while that of GroEL/GroES alleviated the protein export defect of ftsH mutants. These results suggest that FtsH functions can be somehow compensated for when the cellular concentrations of some molecular chaperones increase.