Physical Mapping of the Virion and the Prophage DNAs of a Temperate Lactobacillus phage oFSW

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Abstract
The physical structure of the DNA of .vphi.FSW, a temperate phage of L. casei S-1, was analyzed. A circular restriction map of the virion DNA was constructed with 3 restriction endonucleases, BamHI, SalI and XhoI. Other data indicated that the phage genome was circularly permuted. In lysogens, the DNA of the prophage as found to be linearized at a specific site and integrated into a specific locus of the host genome, with the same orientation in each case, as evidenced by Southern filter hybridization. The physical structure of .vphi.FSW was compared with those of its 3 virulent mutants. One had a restriction map indistinguishable from that of .vphi.FSW and 2 contained host-derived DNA sequence(s) in a specific region of the .vphi.FSW genome (V-region). The prophage integration site was mapped on a different segment of the phage genome to the V-region. Derivation of virulent mutants from .vphi.FSW is discussed in relation to the physical structure of the phage genome.