Construction and analysis of hybrid Escherichia coli Bacillus subtilis dnaK genes

The highly conserved DnaK chaperones consist of an N-terminal ATPase domain , a central substrate-binding domain, and a C-terminal domain whose functio n is not known. Since Bacillus subtilis dnaK was not able to complement an Escherichia coli dnaK null mutant, we performed domain element swap experim ents to identify the regions responsible for this finding. It turned out th at the B, subtilis DnaK protein needed approximately normal amounts of the cochaperone DnaJ to be functional in E, coli, The ATPase domain and the sub strate-binding domain form a species-specific functional unit, while the C- terminal domains, although less conserved, are exchangeable. Deletion of th e C-terminal domain in H. coli DnaK affected neither complementation of gro wth at high temperatures nor propagation of phage lambda but abolished degr adation of sigma(32).