Physical map of a 470 × 10 3 base-pair region flanking the terminus of DNA replication in the Escherichia coli K12 genome

Abstract

In a dnaC28 mutant population synchronized by temperature shifts, the DNA replication rate after initiation is constant for 32 to 34 minutes at 40.5 °C, and then decreases exponentially with a half-time of two minutes to a residual relative rate of 2 to 3%. The DNA of a dnaC28 strain carrying a prophage Mu in the trp operon was labeled during the period of exponential decrease. After lysis the DNA was digested by EcoRI, HindIII or PstI endonucleases, and fractionated on agarose gels. Fractionated DNA from each track was isolated from gel slices and was digested further by the appropriate second and third enzymes and by a mixture of these enzymes. The resulting double and triple digestion products were separated by electrophoresis and were subjected to a fluorographic analysis. From the data obtained a 470 kb † † Abbreviation used: kb, 10 3 base-pairs. restriction map of the DNA flanking the Escherichia coli K12 terminus of replication has been deduced.