Fig 1.

Potential advantageous effects of phage-encoded orphan MTases (see text for further details). (A) Methylation of the GATC sites within the pac region of the phage P1 genome by a self-encoded DAM MTase facilitates the efficient release of progeny phage. Generation of both dam mutant hosts and dmt⁻ phage (phage DAM knockout) prevents methylation of the phage DNA during packaging, leading to a decreased level of phage progeny released. (B) Protection of phage genomes from host-encoded restriction endonucleases through the protection afforded by the phage-encoded orphan MTase. (C) DAM methylation is essential for lysogeny of the Shiga toxin-encoding phage 933W and release of Shiga toxin by EHEC. Loss of GATC methylation results in release of integrated phage and loss of Shiga toxin production by EHEC. Me, methyl group.