3 CLUSTERED ORIGINS OF REPLICATION IN A PROMISCUOUS-PLASMID REPLICON AND THEIR DIFFERENTIAL USE IN A POLA+ STRAIN AND A DELTA-POLA STRAIN OF ESCHERICHIA-COLI K-12

A 1,197-bp region of the broad-host-range plasmid pCU1 is adequate for its replication. Analysis of replicating molecules containing this region reveals three clustered origins of vegetative replication and replication proceeds bidirectionally from each in a theta mode. In an Escherichia coli polymerase I deletion mutant, utilization of one of these three origins was not detected. The potentiality for origin utilization may therefore be a determinant of replicon host range.