Chaperones are conservative proteins present in three kingdoms of life: bacteria, archaea and eukaryotes, with the main responsibility for assisted protein folding. Thermophilic organisms were also found to provide a complex cellular machinery of molecular chaperones. The question how thermophiles adapt could be addressed to the organization of the chaperone system also because chaperones must meet the general requirements that affect every enzymatic function at an elevated temperature. Despite the sequence homology of chaperones from thermophilic and mesophilic organisms, the organization of the hsp70 cluster differs. The clpB gene is not included into the hsp70 gene cluster of the moderately thermophilic bacterium Meiothermus ruber, but it was detected far away from the hsp70 operon. ClpB from M. ruber is the second chaperone of this family, identified in thermophilic organisms so far, and it shows a high sequence homology to the T. thermophilus protein. The internal translation site of M. ruber ClpB upon expression in E. coli cells results in full-length and truncated proteins.

Keywords: Meiothermus ruber, chaperones, hsp70 operone, clpB gene