Toluene-treated Escherichia coli replicate only that DNA which was about to be replicated in vivo.

DNA density-transfer experiments with Escherichia coli strain B/r indicate that the DNA synthesized from exogenous substrates after treatment with toluene is made semiconservatively from that region of the chromosome about to be replicated at the time of toluene treatment. Up to 15% of the chromosome is replicated, at a rate 10-20% of that in vivo. A minor fraction of nonconservatively replicated DNA is readily distinguished.