Viral infections disturb the host physiological balance and can trigger host antiviral defense systems. Some of these defense systems alter vital cellular processes by blocking a crucial step of virus multiplication and ending up with the host cell dormancy or even death .
The blockage is mediated by host proteins, designed here as toxins, that are activated upon infection. The vast majority of toxins found so far interfere with the translation process, mostly via mRNA or tRNA cleavage .
Some of these toxins are part of a toxin-antitoxin system (TA) where the toxin is normally kept inactive by the antitoxin. Some toxins have been named Abi (abortive infection) according to the fatal outcome .
Prokaryotic viruses can counteract these defense systems by making up for the altered function or by mimicking the antitoxin molecule in order to protect themselves against the negative effects of toxin activation.
Here are some examples of viruses counteracting the host translational shutoff:
|Family||Genus||Virus||Host bacteria||Bacterial toxin||Toxin activation||Toxin activity||Viral evasion strategy||Ref.|
|Myoviridae||unclassified||ΦTE||Pectobacterium atrosepticum||ToxN||Degradation of antitoxin ToxI||mRNAs site-specific endoribonuclease||Viral pseudo-ToxI RNA|
|Myoviridae||Punalikevirus||Enterobacteria phage P1||E.coli||MazF||Degradation of antitoxin MazE||mRNAs site-specific endoribonuclease||?|
|Myoviridae||T4likevirus||Enterobacteria phage T4||E.coli||RnlA||Degradation of antitoxin RnlB||mRNAs endoribonuclease||Viral antitoxin Dmd|
|Myoviridae||T4likevirus||Enterobacteria phage T4||E.coli||LsoA||Degradation of antitoxin LsoB||mRNAs endoribonuclease||Viral antitoxin Dmd|
|Myoviridae||T4likevirus||Enterobacteria phage T4||E.coli||PrrC||By T4 Stp||tRNALys anticodon nuclease||T4 polynucleotide kinase or RNA ligase repair enzymes|
|Myoviridae||T4likevirus||Enterobacteria phage T4||E.coli||LitA||Complex of T4 Gol and host EF-Tu||Host EF-Tu cleavage||Mutations in Gol|
|Siphoviridae||unclassified||Lactococcus phage P008||L.lactis||AbiQ||Degradation of antitoxin mRNA||Endoribonuclease||gp38 mediated?|