Map position of the replication origin on the E. coli chromosome.

Strains carrying a dnaA temperature sensitive (t.s.) mutation and a Mu-1 prophage inserted within different genes near the origin of replication have been constructed. For each strain, integratively suppressed Hfrs, named G and D in which the ori region was replicated clockwise and counterclockwise respectively, were isolated. The strand preferences of Mu-1 specific Okazaki fragments were subsequently determined for each t.s. strain and its Hfr derivatives. Their comparison led us to establish the direction of replication of the Mu-1 marker from ori. The site ori was confined to the bglB-C--rbsK-P interval.