The appearance of circular DNA after lysogenic induction in Escherichia coli CR34(lambda).

A circular (non-ended) form of DNA is synthesized both after ultraviolet light and after thymineless induction of the lysogen Escherichia coli CR34(lambda). This new DNA species is shown to have characteristics identical to the circular DNA formed from lambda phage DNA immediatelyafter infection. Thus, the formation of a circular lambda DNA isnot limited to that derived directly from an infecting phage DNA but is also formed during the normal replication of the lambda DNA after lysogenic induction. The circular lambda DNA formed after lysogenic induction contains no detectable amounts of the bacterial genome. Once formed in the cell, the circular DNA species is stable and not significantly degraded.