The Mok Hok Sok system was discovered as a type 1 toxin-antitoxin system to stabilize plasmid R1 :ref{doi=10.1128/jb.161.1.292-298.1985}. Sok (Suppression of Killing) is an RNA and serves as the antitoxin. Hok (Host killing) is the toxin and Mok (Modulation of killing) is required for the expression of Hok :ref{doi=10.1016/j.mib.2007.03.003,10.1093/nar/gkl750}.
Hok/sok are not related to the T4 head protein Hoc and Soc.
This system defends against T4 phages only, as far as we currently know.
## Molecular mechanism
Upon infection of phage T4, the transcription is halted by the phage, which leads to a decreasing level of the antitoxin Sok within a few minutes. The Hok proteins manage to be process in their active form and trigger cell death by depolarization of the membrane :ref{doi=10.1006/jmbi.1995.0186} before the later stage of the phage infection (assembly, packaging and lysis).
## Example of genomic structure
The Mok_Hok_Sok is composed of 2 proteins: Mok and Hok.
...
...
@@ -51,7 +68,7 @@ graph LR;
Pecota_1996[<ahref='https://doi.org/10.1128/jb.178.7.2044-2050.1996'>Pecota and Wood, 1996</a>] --> Origin_0