Physical mapping of the genomes of lytic and temperate forms of phage theta

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Abstract
Restriction maps of genomes of the lytic form and diverse temperate mutants of phage ϱ of Bacillus licheniformis were constructed. Most temperate mutants produced fragmentation patterns identical to that of the parent lytic form, ϱc: in other mutants the only detectable change in the map was the deletion of a BglII restriction endonuclease site at 46.5% genome length. In the genomes of two other temperate mutants, ϱ1 and ϱ2, the central part of the genome was replaced by a piece of DNA of equal length, but with a different distribution of restriction sites; the maps of the two mutants failed to reveal any similarity in the location of restriction sites in the inserted DNA. It seems that any alteration comprising the locus around the coordinate 46.5% of the ϱc genome, brings about a transition from the lytic to temperate phenotype, indicating the position of a regulatory gene responsible for positive control of phage replication.