Isolation of Plasmid‐Protein Complexes from Escherichia coli

Abstract

A procedure is described for the isolation of complexes between pMB9 plasmids and protein from E. coli which are stable during centrifugation on sucrose gradients and are not destroyed in the presence of competitor DNA. The proteins in these complexes were analyzed by dodecyl sulfate/polyacrylamide gel electrophoresis. Only 10 polypeptide species are found in significant quantities, many of which are bound to the plasmid and host DNA. The presence of 1 protein which binds to a specific DNA sequence inserted in the plasmid was also detected.