Deletions in bacteriophage P2. Circularity of the genetic map and its orientation relative to the DNA denaturation map.

Several types of viable chromosomal deletions of bacteriophage P2 were isolated. One type gives the immunity insensitive phenotype and may extend to the genes for the immunity repressor (C) and for integrative recombination (int). Two other types delete genes (old and fun) known to be active in the lysogenic state. For such deletion mutants the relationship between particle density and DNA length was established. The deletions were located in respect to previously mapped genes and the results were compared with electron microscopical studies (by Inman and collaborators) of the P2 chromosome. It is concluded that the best representation of the genetic map of P2 is circular. The cohesive ends of the linear P2 DNA molecule are most likely formed between genes old and Q. Except for the neighborhood of gene old, the previously published, linear genetic map of P2 (Lindahl) is colinear with the melting map of the P2 chromosome (Inman). Preliminary evidence for some specific recombination event often accompanying integrative recombination between phage chromosomes is presented.