Sequence comparison of the genes for immunity, DNA replication, and cell lysis of the P22-related Salmonella phages ES18 and L.

Complementation and hybridization experiments with the generalized transducing Salmonella phages P22, ES18 and L revealed strong similarity between the phages L and P22; the genome of ES18 shows a mosaic structure. About half of its genome, including the early genes, is similar or completely homologous to P22; the other half of the morphologically different ES18 does not show any similarity to P22 nor to E. coli phage lambda. Sequence comparison of the early genes has confirmed that the C-immunity region of ES18 is identical with that of P22, whereas the same region of phage L shows poor (repressor gene) or no similarity. The 5'-terminus of the DNA replication gene 12 of ES18, however, is homologous to the same section of gene O of phage lambda. The lysis genes of ES18 again are identical to those of P22; only gene 15 is mosaic-like and has more similarity to gene Rz of phage lambda. These results will be discussed in terms of the theory of modular genome organization.