Characterization and radio-resistant function of manganese superoxide dismutase of rubrobacter radiotolerans

Rubrobacter radiotolerans is the most radio-resistant eubacterium without spore-formation in the life cycle,and its d37 is 16,000 gy against gamma-rays. to understand the molecular mechanism of the high radio-resistance,we purified and characterized superoxide dismutase (sod) of this organism as enzymatic radical scavenger,and then analyzed its genetic information. the purified sod protein formed homo-tetramerization of 24,000 da-monomer,while maintaining its enzymatic activity against potassium cyanide and hydrogen peroxide. we obtained a partial amino acid sequence of the protein and cloned the gene from it. sequence analysis of the cloned gene indicated that the protein showed a similarity to other bacterial manganese sods (mn-sods). sequencing for adjacent regions of the gene showed that the gene had promoter elements with an open reading frame for putative pas/pac sensor protein at the 5'-adjacent region. introduction of the gene into escherichia coli cells lacking intrinsic sod genes restored the cellular enzymatic activity and resistance to methyl viologen,indicating the gene at work. a mutant cell harboring this gene also became resistant against gamma-rays. the present results suggest that the protein in question is the mn-sod of r. radiotolerans,a good candidate as a radio-protection factor for this bacterial radio-resistance.