DarTG
Description
The DarTG defense system is a toxin-antitoxin (TA) system that provides defense against bacteriophages by ADP-ribosylating viral DNA, thereby preventing replication and the production of mature virions. This system consists of two subfamilies, DarTG1 and DarTG2, which protect against different phages. When infected by specific phages, the DarT toxin, a DNA ADP-ribosyltransferase, is released, modifying viral DNA and inhibiting replication.
Molecular mechanism
DarT uses NAD+ to ADP-ribosylates thymidine on ssDNA, while DarG catalyzes the reverse reaction. ADP-ribosylation of ssDNA prevents DNA replication and triggers the cell's SOS response. While initially proposed to work on bacterial ssDNA as a TA system (N/A) , Leroux et al. (N/A) show that it mostly modifies viral DNA and therefore blocks viral replication and perturb the transcription of phage genes. They conclude that "DarTG does not ultimately kill the host cell as in a conventional Abi mechanism, but instead acts to thwart phage replication directly."
Example of genomic structure
The DarTG is composed of 2 proteins: DarT and DarG.
Here is an example found in the RefSeq database:
The DarTG system in Leptodesmis sichuanensis (GCF_021379005.1, NZ_CP075171) is composed of 2 proteins DarT (WP_233744308.1) DarG (WP_233744309.1)
Distribution of the system among prokaryotes
Structure
Group | Structure | Foldseek | System | Gene name | Subtype | Proteins in structure | System genes | Prediction type | N genes in sys | pLDDT | iptm+ptm | pDockQ |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| No data available | ||||||||||||