The Na+ pump-deficient mutant, Napl, of Vibrio alginolyticus was found to lack three subunits of Na+-dependent NADH:quinone oxidoreductase complex. Although a spontaneous Na+ pump positive revertant did not appear from Napl, transconjugants that recovered both the Na+ pump activity and the subunits were isolated from Napl conjugated with the wild type. Moreover, the wild type was found to contain two different sizes of plasmids. These results suggest the possibility that the Na+ pump is encoded by a plasmid.
