SUMMARY: A mutant strain of , strain AK23, is devoid of hydrogenase activity when grown anaerobically on glucose and cannot grow on H plus fumarate. From an chromosomal DNA library, a plasmid, pAK23, was isolated which restored hydrogenase activity in this strain. Two smaller plasmids, pAK23C and pAK23S, containing different parts of the insert DNA fragment of plasmid pAK23, were isolated. The former plasmid restored activity in strain AK23 while the latter did not. The smallest active DNA fragment in plasmid pAK23C was 0.9 kb. This gene is designated Plasmids pAK23 and pAK23S restored activity in another hydrogenase-negative strain, SE-3-1 (), while plasmid pAK23C did not, suggesting that plasmid pAK23 contains two genes required for hydrogenase expression. Strain AK23 was also devoid of formate hydrogeniyase and formate dehydrogenase activities and these activities were restored by some of the plasmids. Hydrogenase and formate-related activities in strain AK23-were restored by growth of cells in a high concentration of nickel. Plasmid pAK23C led to synthesis of a polypeptide of subunit molecular mass 36 kDa and plasmid pAK23S led to synthesis of polypeptides of subunit molecular masses 30 and 41 kDa.


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