HIGH-AFFINITY BINDING OF HEMIMETHYLATED ORIC BY ESCHERICHIA-COLI MEMBRANES IS MEDIATED BY A MULTIPROTEIN SYSTEM THAT INCLUDES SEQA AND A NEWLY IDENTIFIED FACTOR, SEQB

The binding of hemimethylated oriC to Escherichia coli membranes has b een implicated in the prevention of premature reinitiation at newly re plicated chromosomal origins in a reaction that involves the SeqA prot ein. We describe the resolution of the membrane-associated oriC-bindin g activity into two fractions, both of which are required for the high -affinity binding of hemimethylated oriC, The active component in one fraction is identified as SeqA, The active component of the second fra ction is a previously undescribed protein factor, SeqB, The reconstitu ted system reproduced the salient characteristics of the membrane-asso ciated binding activity, suggesting that the membrane-associated oriC- binding machinery of E. coli is likely to be a multiprotein system tha t includes the SeqA and SeqB proteins.