Recombination involving transposable elements: role of target molecule replication in Tn1 delta Ap-mediated replicon fusion.

Donor DNA molecules carrying Tn1 or Tn3 deletion 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 Tn1 delta Ap-mediated replicon fusion events involving plasmid R388 and the bacteriophage lambda-derived plasmid p lambda CM, and we find that the role of the recipient molecule is distinct. When p lambda CM carries Tn1 delta Ap, replicon fusion occurs in more than 1% of all cells assayed, whether or not p lambda CM::Tn1 delta Ap can replicate. In contrast, when R388 carries Tn1 delta Ap, replicon fusion occurs only when the p lambda CM target can replicate. Blocks to p lambda 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 10(5) cells assayed.