Physiological consequences of the over-production of E. coli truncated molecular chaperone DnaJ

In Escherichia coli one of the main molecular chaperones is DnaJ (hsp40) which mediates in a variety of highly conserved cellular process including protein folding reactions and assembly/disassembly of protein complexes. In this study we have investigated the toxicity of the over-production of DnaJ and two truncated polypeptides by examining growth rates, cell morphology and cell viability. Full-length DnaJ (1-375 amino acids) and truncated polypeptides, corresponding to the last 176 (containing the substrate binding domain) and 266 (containing the zinc finger-like domain) amino acids of the C-terminus of DnaJ, DnaJ delta 1-199 and delta 1-108 respectively, were over-produced via IPTG induction. High levels of synthesis were determined by SDS-PAGE and Western blotting using anti-DnaJ antibodies. The over-production of full-length DnaJ resulted in a low degree of filamentation and a decrease in cell viability. However, over-production of DnaJ truncated polypeptides, especially DnaJ delta 1-108, was bactericidal and resulted in a loss of viability and defective septation.