FIG 2.

Maps showing features common in the origin regions of plasmid P1 and chromosome 2 (Chr2) of V. cholerae. Both regions have a DnaA binding site (black pentagon), an AT-rich region (A+T), multiple initiator binding sites (gray hexagons) (called iterons in plasmids and 12-mers in Chr2), and an autorepressed initiator gene (repA and rctB, respectively). Autorepression is achieved by RepA binding to iterons in P1 and RctB binding to a 29-mer (red square), which is unrelated to 12-mers in sequence. P indicates promoters. The minimal regions that suffice as origins are marked as P1ori and ori2. The iterons and 12-mers outside P1ori and ori2 (called incA and inc2) reduce origin activity, although in Chr2, the activity of inc2 12-mers reverses in the presence of another regulator (39-mer) (shown in Fig. 7).