Plasmid-phage recombination in T7 infected Escherichia coli

Recombination between genetically marked T7 bacteriophage and plasmids containing inserts of T7 DNA has been studied in order to gain some insight into the phage recombination process. The results suggest that plasmid-phage recombination requires the products of T7 genes 3 (endonuclease), 4 (DNA primase), 5 (DNA polymerase), and 6 (exonuclease), as has been demonstrated previously for phage-phage recombination. Plasmid replication does not compensate for a complete block in phage polymerase synthesis, suggesting a direct role for this enzyme in recombination, rather than an indirect role, by means of producing replicative structures that are recombinogenic. In most respects, plasmid-phage recombination appears to be similar to phage-phage recombination. The participation of two autonomous, structurally dissimilar, homologues, however, might render certain aspects of the recombination process more amenable to analysis. As examples, the characterization of an apparent marker effect and the demonstration of genetic heterozygotes among the products of plasmid-phage recombination are presented.