RADAR

Contributors: Hugo Vaysset, Aude Bernheim

Description

RADAR (Restriction by an Adenosine Deaminase Acting on RNA) is comprised of two genes, encoding respectively for an adenosine triphosphatase (RdrA) and a divergent adenosine deaminase (RdrB), which are in some cases associated with a small membrane protein (RdrC or D). They were first uncovered in a study exploring the content of defense islands ()

Molecular mechanism

In the initial study describing RADAR, RADAR was found to perform RNA editing of adenosine to inosine during phage infection () . Editing sites were broadly distributed on the host transcriptome, which could prove deleterious leading to observed growth arrest of RADAR upon phage infection.   Further structural studies revealed potentially different mechanisms of actions (, ) . RdrA and RdrB assemble to form a giant 10 MDa complex. The RADAR defense system limits phage replication by catalyzing ATP deamination. Within this system, RdrB functions as an adenosine deaminase, leading to the buildup of ITP (Inosine Tri-Phosphate) and dITP. RdrA induces RdrB activity and potentially regulates the detection of phage infections.

Example of genomic structure

A total of 2 subsystems have been described for the RADAR system.

Here is some examples found in the RefSeq database:

The radar_I system in Vibrio splendidus (GCF_022812155.1, NZ_CP089205) is composed of 2 proteins rdrA_I (WP_243585344.1) rdrB_I (WP_243585345.1)

The radar_II system in Enterobacter sp. JH25 (GCF_021725435.1, NZ_CP091319) is composed of 3 proteins rdrD_II (WP_022649082.1) rdrB_II (WP_227746616.1) rdrA_II (WP_022649084.1)

Distribution of the system among prokaryotes

Among the 22,803 complete genomes of RefSeq, the RADAR is detected in 135 genomes (0.59 %).

The system was detected in 44 different species.

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

Structure

Experimentally determined structure

From () in Escherichia coli:

From () in Streptococcus suis:

From () in Escherichia coli:

radar_I

Example 1

radar_II

Example 1

Experimental validation

      
graph LR;
    Gao_2020[Gao et al., 2020] --> Origin_0
    Duncan-Lowey_2022[Duncan-Lowey et al., 2023] --> Origin_0
    Origin_0[Citrobacter rodentium 
WP_012906049.1, WP_012906048.1] --> Expressed_0[Escherichia coli]
    Expressed_0[Escherichia coli] ----> T2 & T4 & T5 & T3 & T6
    Duncan-Lowey_2022[Duncan-Lowey et al., 2023] --> Origin_1
    Origin_1[Escherichia coli 
2548796856, 2548796855] --> Expressed_1[Escherichia coli]
    Expressed_1[Escherichia coli] ----> T2 & T4 & T6
    Duncan-Lowey_2022[Duncan-Lowey et al., 2023] --> Origin_2
    Origin_2[Streptococcus suis 
2706833061, 2706833062] --> Expressed_2[Escherichia coli]
    Expressed_2[Escherichia coli] ----> T2 & T4 & T5 & T6
    subgraph Title1[Reference]
        Gao_2020
        Duncan-Lowey_2022
end
    subgraph Title2[System origin]
        Origin_0
        Origin_0
        Origin_1
        Origin_2
end
    subgraph Title3[Expression species]
        Expressed_0
        Expressed_0
        Expressed_1
        Expressed_2
end
    subgraph Title4[Protects against]
        T2
        T4
        T5
        T3
        T6
        T2
        T4
        T5
        T3
        T6
        T2
        T4
        T6
        T2
        T4
        T5
        T6
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

10.1016/j.cell.2023.01.026
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10.1016/j.cell.2023.01.012
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10.1126/science.aba0372
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