Origin and Sequence of Chromosome Replication in Escherichia coli B/r

Charles E. Helmstetter
1968 Journal of Bacteriology  
The initial rates of induced synthesis of tryptophanase, 3-galactosidase, and Dserine deaminase were measured in relation to the chromosome replication cycle of Escherichia coli B/r. Exponentially growing cultures were exposed briefly to 14Cthymidine or the appropriate inducers (or both), and the amount of label or enzyme (or both) in cells of different ages was found by measuring these quantities in their progeny. The rates of induced synthesis of the three enzymes increased abruptly at about
more » ... abruptly at about 4, 20, and 34 min, respectively, after the start of a round of replication lasting 40 min. By matching this sequence to the ind, lac, and Dsdloci on the genetic map of E. coli K-12, it was estimated that replication began at about 8 o'clock (60 min) and proceeded clockwise. In rapidly growing cells, the sequence during the division cycle was consistent with the concept that rounds of replication overlapped.
doi:10.1128/jb.95.5.1634-1641.1968 fatcat:p54htx5jtvhjhclhwypt7u77s4