Purification and characterization of a low-molecular-weight membrane protein with affinity for the Escherichia coli origin of replication.

A purification procedure was devised for a low-molecular-mass (about 10-kilodalton) membrane protein from Escherichia coli that was shown to bind specifically to the chromosomal replication origin region (oriC). Nitrocellulose membrane retention assays showed the binding site to be adjacent to the right boundary of the oriC minimal sequence. We determined the amino acid sequence of the N-terminal and C-terminal regions as well as the global amino acid composition of this membrane protein. Specific antibodies against the protein were produced and used to confirm the cell membrane location of the protein. These results demonstrate that this is a new membrane protein, different from the previously described B' protein, with specific binding activity for the oriC region. We propose that this protein be called membrane oriC-binding protein 2 (MOB2 protein).