Chapter 25 DnaJ homologs and protein transport

Abstract

Abstract A variety of intracellular protein transport processes require or are stimulated by members of the evolutionarily conserved 70 kDa heat shock protein (HSP70) family and other unidentified factors. The ability of HSP70s to control protein folding and assembly is thought to be the basis for their role in protein transport. In Escherichia coli, genetic and biochemical evidence suggests that the unique bacterial HSP70, DnaK, does not act alone but functions in concert with two other heat shock proteins, DnaJ and GrpE, to mediate such protein folding and assembly. Complete and partial DnaJ homologs have now been identified in other bacterial species as well as in the yeast, Saccharomyces cerevisiae . Genetic evidence suggests a role in protein transport for three of the four yeast homologs. Based on the functional complex of DnaJ and DnaK in E. coli , we propose that DnaJ homologs will interact with HSP70s via an evolutionarily conserved 'J-region' to mediate protein folding and assembly reactions important for protein transport processes. It will be of great interest to determine if the unidentified factors that are required along with HSP70s for maximum stimulation of some transport processes correspond to DnaJ homologs.