Expression of subunits a and c of the sodium-dependent ATPase of Propionigenium modestum in Escherichia coli.

The aim of the present study was to construct functional hybrid ATPases consisting of all Escherichia coli ATPase subunits excepts the F0 subunits a or c which were replaced by the respective subunits of the Propionigenium modestum ATPase. This would give valuable information on the subunit(s) conferring the coupling ion specificity. Plasmids were constructed that carried the gene for subunit c (uncE) or subunit a (uncB) behind a tac promoter. These plasmids were transformed into E. coli strains which differed with respect to the unc operon and the expression of the P. modestum genes was verified biochemically. Enhanced expression of the P. modestum genes led to strong growth inhibition of all E. coli strains tested. However, the expressed P. modestum proteins could not functionally complement E. coli strains that lacked the homologous subunit.