the fo subunits of the escherichia coli f1foatp synthase are sufficient to form a functional proton pore the assembly of the fo sector of the escherichia coli atp synthase has been studied using both structural and functional criteria for assembly crosslinking e coli minicell membranes containing only the fo subunits a b and c with dithiobissuccinimidyl propionate dsp produces b2 and c2 dimers that are generated by crosslinking membranes containing the assembled holoenzyme five plasmids carrying the genes specifying the fo polypeptides in a bacterial strain lacking all of the unc atp synthase genes show a good correlation between fo function and the amount of the membranebound fo polypeptides in this report we revise a conclusion reached previously klionsky dj brusilow wsa and simoni rd 1983 j biol chem 258 1013610143 and present evidence that the fo subunits alone are sufficient to assemble a functional proton pore