Physiological transition of a coliphage lambda DNA replication.

The "rolling-circle" replicative intermediate (sigma-type molecules) which is normally produced in the late stage of coliphage lambda DNA replication can be found during the first round of lambda DNA replication if cells infected with lambda replication mutant Ots28 are incubated at the nonpermissive temperature until the late stage of the latent period of lambda infection. After shifting to the permissive temperature, the vast majority of replicating forms are sigma-type rolling circle even during the first round of DNA replication. Concatemeric lambda DNA molecules, produced from these sigma-type intermediates, are efficiently packaged into progeny phage, indicating that in the first round of lambda DNA replication, double-branched theta-type molecules are not required for production of viable progeny phage.