The Escherichia coli SeqA protein binds specifically to two sites in fullyand hemimethylated oriC and has the capacity to inhibit DNA replication and affect chromosome topology

The SeqA protein was identified as a factor that prevents reinitiation of n ewly replicated, hemimethylated origins. SeqA also seems to inhibit initiat ion of fully methylated origins, thus contributing to the regulation of chr omosomal replication. The SeqA protein was found to bind to two sites in th e left part of the origin, near the AT-rich region where strand separation takes place during initiation of replication. The same binding sites seemed to be preferred irrespective of whether the origin was in the newly replic ated (hemimethylated) state or not. In addition to binding specifically to groups of GATC sites, the SeqA protein was capable of interacting non-speci fically with negatively supercoiled DNA, restraining the supercoils in a fa shion similar to that seen with histone-like protein HU. The restraint of s upercoils by SeqA was, in contrast to that of HU, cooperative. (C) 2001 Soc iete francaise de biochimie et biologie moleculaire / Editions scientifique s et medicales Elsevier SAS.