Replication fork in a P1 lysogen. Modified from Meisel et al. (132). The asymmetric EcoP1 recognition sequences are represented by differentially shaded arrows, with the arrowheads pointing in the direction of the cleavage sites. In the parental DNA molecule all EcoP1 sites are methylated (indicated by circles). In the two daughter molecules only those sites that inherited a methyl group are modified. However, as in each daughter molecule all unmodified sites have the same orientation, no convergently tracking enzyme complexes will collide and thus the daughter molecules are not cleaved. EcoP1 enzyme complexes trailing the replication forks will then de novo modify the unmetylated sites, ensuring continued protection for the next round of replication (133).