Map location of the Escherichia coli origin of replication

Working with restriction fragments obtained directly from the Escherichia coli K12 chromosome, the EcoRI-HindIII restriction map of the section of the chromosome containing the replication origin has been extended by 14 kilobase pairs (kb) to cover 56 kb. Within this newly mapped portion, the ilv and rrnC cistrons have been identified by (1) hybridization of individual restriction fragmanents to the ilv-transducing phage lambdadilv5 and (2) a comparison of the restriction map of this region with the EcoRI map of lambda dilv5 and the Hind III map of the plasmid pJC110, a ColEl-ilv hybrid. The replication origin is located approximately 30 kb from the ilvE gene and 20 kb from the rrnC 16S rRNA cistron. This places the origin near 82.7 min on the genetic map, close to uncA.