Recombination Involving Transposable Elements: Role of Target Molecule Replication in Tn1Δ Ap-Mediated Replicon Fusion

Donor DNA molecules carrying Tn1 or Tn3 delection mutants do not need to replicate in order to participate in replicon fusion recombination events during which the Tn1/Tn3 element is duplicated. We have assayed Tn1Δ Ap-mediated replicon fusion events involving plasmid R388 and the bacteriophage λ -derived plasmid pλ CM, and we find that the role of the recipient molecule is distinct. When pλ CM carries Tn1Δ Ap, replicon fusion occurs in more than 1% of all cells assayed, whether or not pλ CM::Tn1Δ Ap can replicate. In contrast, when R388 carries Tn1Δ Ap, replicon fusion occurs only when the pλ CM target can replicate. Blocks to pλ CM replication by prophage repressor or amber mutations of the O and P cistrons reduce replicon fusion so that it occurs in less than 1 out of 105cells assayed.