A 245 bp segment of E. coli chromosomal replication origin, oriC, contains 11 repeats of the GATC sequence in which adenine is methylated by Dam methylase. Newly replicated oriC is hemimethylated. The parental strand of the newly replicated oriC is methylated, but the nascent strand is not yet methylated until methylated by Dam methylase. The hemimethylated oriC plays an important role in the regulation of chromosomal replication. Activity in the seqA mutant was identified to bind preferentially to hemimethylated DNA, but not to fully-methylated DNA. This activity may participate in the sequestration of initiation of chromosomal replication.