Characterization of in vivo chaperone function by the rescue of nonfunctional missense mutants

Chaperones play a fundamental role in facilitating the proper folding of intracellular proteins. They rescue misfolded or damaged proteins and allow them the opportunity to refold into an enzymatically active form. While previous studies of chaperone proteins have focused on in vitro folding characteristics, this research provides an intracellular examination of chaperone function by analyzing the ability of either GroELS or DnaKJ to rescue misfolded proteins in vivo. Libraries of non-functional missense mutants were obtained for the hisC and hisD genes from Salmonella typhimurium and the lacY, lacZ, and trpA genes from Escherichia coli. Overexpression vectors containing either the dnaKJ or groELS genes from E. coli were introduced into each missense mutant. Twenty-five percent of the 185 inactive missense mutants tested could be suppressed by the overproduction of either DnaKJ or GroELS. The percentage of overlap between the specific mutant alleles that could be suppressed by both chaperones was significant.