Progress in the resolution of the cytoplasmic membrane DNA initiation complex of Escherichia coli.

The attachment of the bacterial chromosome to the cytoplasmic membrane in Escherichia coli was studied. The initiator DNA was specifically labeled and the outer and cytoplasmic membranes were separated in a step sucrose gradient. The labeled DNA was localized mainly in the cytoplasmic membrane fraction. The DNA . cytoplasmic membrane complex was isolated from cells uniformly labeled with [Me-3H]thymidine, solubilized with deoxycholate and chromatographed on Sepharose 4B. A high percent of the labeled DNA was excluded in the void volume but a small fraction eluted associated with the second protein elution peak. The isolation of such a DNA . cytoplasmic membrane protein complex, suggests useful strategies for future studies about the molecular components of the initiation complex in E. coli.