Cloning and characterization of the Brucella ovis heat shock protein DnaK functionally expressed in Escherichia coli

The Brucella ovis dnaK gene, homolog to the eukaryotic hsp70 genes, was cloned by using a Drosophila melanogaster probe. Comparison of B. ovis and Escherichia coli sequences revealed a similar organization for the dnaK and dnaJ genes and putative regulatory signals. In E. coli transfected with the cloned fragment, B. ovis hsp70 was expressed at 30 and 50 degrees C apparently under the control of its own promoter. The recombinant protein and a B. ovis native protein displaying the same molecular weight were both recognized by anti-E. coli DnaK serum. Native B. ovis protein was also recognized by sera of sheep either infected or vaccinated with an attenuated Brucella strain, suggesting that Brucella hsp70 could be up-regulated during host colonization. A thermosensitive E. coli dnaK mutant transfected with the cloned fragment recovered colony-forming ability at 42 degrees C, showing that the B. ovis DnaK protein could behave as a functional heat shock protein in E. coli.