Figure 4.

Map of the replication and partitioning region of pAD1. Two clusters of iterons (TAGTARRR) are shown between repA and repBC. Isolated iteron sequences are also located within the promoters of repA and repBC. RepC binds cooperatively to iteron sequences; in the presence of ATP, RepB also binds. RepC binding to the isolated iterons probably affects expression of repBC and repA. A “folded” conformation may be stabilized by the binding and effect interaction between the opposing promoters. Phase variation resulting from changes in the number of iterons could affect this interaction and modulate expression of RepBC and RepA (redrawn from ref. 131).