THE RELATIONSHIP BETWEEN HETERO-OLIGOMER FORMATION AND FUNCTION OF THE TOPOLOGICAL SPECIFICITY DOMAIN OF THE ESCHERICHIA-COLI MINE PROTEIN

MinE is an oligomeric protein that, in conjunction with other Min prot eins, is required for the proper placement of the cell division site o f Escherichia coli. We have examined the self-association properties o f MinE by analytical ultracentrifugation and by studies of hetero-olig omer formation in non-denaturing polyacrylamide gets. The self-associa tion properties of purified MinE predict that cytoplasmic MinE is like ly to exist as a mixture of monomers and dimers. Consistent with this prediction, the C-terminal MinE(22-88) fragment forms hetero-oligomers with MinE(+) when the proteins are co-expressed. In contrast, the Min E(36-88) fragment does not form MinE(+)/MinE(36-88) hetero-oligomers, although MinE36-88 affects the topological specificity of septum place ment as shown by its ability to induce minicell formation when co-expr essed with MinE(+) in wild-type cells. Therefore, hetero-oligomer form ation is not necessary for the induction of mini-celling by expression of MinE(36-88) in wild-type cells. The interference with normal septa l placement is ascribed to competition between MinE(36-88),nd the corr esponding domain in the complete MinE protein for a component required for the topological specificity of septal placement.