INTEGRATION DEFECTIVE MUTANTS OF BACTERIOPHAGE P2

Mutants of phage P2 unable by themselves to be integrated as prophages have been isolated. These mutants (int) are complemented by the wild type allele and may then yield stable lysogenic strains carrying an int prophage at location I in Escherichia coli C. These lysogens produce either no phage or little phage, depending on the int mutant used. All int mutants isolated appear to belong to a single complementation group. Exceptional lysogens carrying two or more int prophages may be obtained: they may produce spontaneously even more phage than normal lysogens, and they segregate out defective, singly lysogenic clones at low frequency. These exceptional lysogens carry both prophages in location I, presumably in tandem. Strains carrying two or more int prophages but defective in phage production were also isolated. One of these carries its prophages at two different, not closely linked, chromosomal locations. © 1969 Springer-Verlag.