Mok_Hok_Sok

Contributors: Jean Cury

Description

The Mok Hok Sok system was discovered as a type 1 toxin-antitoxin system to stabilize plasmid R1 () . 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 (, ) . 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 processed in their active form and trigger cell death by depolarization of the membrane () 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.

Here is an example found in the RefSeq database:

The Mok_Hok_Sok system in Escherichia fergusonii (GCF_013819565.1, NZ_CP057221) is composed of 1 protein: Hok (WP_096937776.1)

Distribution of the system among prokaryotes

Among the 22,803 complete genomes of RefSeq, the Mok_Hok_Sok is detected in 1656 genomes (7.26 %).

The system was detected in 83 different species.

Proportion of genome encoding the Mok_Hok_Sok system for the 14 phyla with more than 50 genomes in the RefSeq database.

Structure

Mok_Hok_Sok

Example 1

Experimental validation

      
graph LR;
    Pecota_1996[Pecota and  Wood, 1996] --> Origin_0
    Origin_0[R1 plasmid of Salmonella paratyphi 
WP_001372321.1] --> Expressed_0[Escherichia coli]
    Expressed_0[Escherichia coli] ----> T4
    subgraph Title1[Reference]
        Pecota_1996
end
    subgraph Title2[System origin]
        Origin_0
end
    subgraph Title3[Expression species]
        Expressed_0
end
    subgraph Title4[Protects against]
        T4
end
    style Title1 fill:none,stroke:none,stroke-width:none
    style Title2 fill:none,stroke:none,stroke-width:none
    style Title3 fill:none,stroke:none,stroke-width:none
    style Title4 fill:none,stroke:none,stroke-width:none

    

References

10.1128/jb.178.7.2044-2050.1996
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10.1016/0022-2836(92)90714-u
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10.1128/jb.161.1.292-298.1985
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10.1016/j.mib.2007.03.003
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10.1093/nar/gkl750
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10.1006/jmbi.1995.0186
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