The iteron regions necessary for the RepE-iteron interaction in vivo in mini-F plasmids of Escherichia coli

We have determined the nucleotide positions of an incC iteron essential for RepE binding by analyzing mutated incC iterons defective in exerting incom patibility towards mini-F plasmids, The mutations affecting this incompatib ility occurred mostly at two positions within the incC iteron, i.e. an iter on conserved position and a mini-F specific position. Most of the herons wi th a base-change at either of these two positions had lost the binding affi nity for RepE. This agrees with the crystallographic structure of the RepE- iteron complex which showed that the N and C terminal domains of RepE inter act with the two major grooves on one face of the iteron DNA. These grooves contain the iteron conserved and mini-F specific positions necessary for R epE binding, Thus the binding mode may be common to in the case of mini-F l ike plasmids.