THE INTERACTION OF REPC INITIATOR WITH ITERONS IN THE REPLICATION OF THE BROAD-HOST-RANGE PLASMID RSF1010

The replication origin of the broad host-range plasmid RSF1010 contain s 3.5 copies of a 20mer iteron sequence that bind specifically to the plasmid-encoded initiator, RepC. Here we demonstrated that even a sing le iteron was bent upon binding of RepC. Moreover, the bending angle s eems to become larger along with the increment of the number of iteron s. In a mutational analysis of the iteron sequence, we isolated seven kinds of base-substitution mutants of iterons, and estimated the repli cation activity of these mutants in vivo. We found that each of the su bsections in the 20mer iteron sequence made a distinct contribution to the initiation of RSF1010 DNA replication. With the binding assay of RepC and mutated iterons in vitro, we found that the formation of a pr oductive RepC-iteron complex was required for the initiation of plasmi d DNA replication.