Polarization of the Escherichia coli chromosome. A view from the terminus

The E. coli chromosome replication arms are polarized by motifs such as RRN AGGGS oligomers, found preferentially on leading strands. Their skew increa ses regularly from the origin to dif(the site in the center of the terminus where chromosome dimer resolution occurs), to reach a value of 90% near di f. Convergent information indicates that polarization in opposite direction s from the dif region controls tightly the activity of dif, probably by ori enting mobilization of the terminus at cell division. Another example of po larization is the presence, in the region peripheral to the terminus, of sm all non-divisible zones whose inversion interferes with spatial separation of sister nucleoids. The two phenomena may contribute to the organization o f the Ter macrodomain. (C) 2001 Societe francaise de biochimie et biologie moleculaire / Editions scientifiques et medicales Elsevier SAS.