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• Prokaryotes have developed various defense mechanisms against viruses.
• CRISPR is one of the processes that protect prokaryotic organisms from viruses.
• CRISPR allows bacteria to remember DNA from invading viruses and chop off viral DNA to stop the infection.
• Researchers studied the relationship between two of the popular prokaryotic immune systems namely CRISPR and restriction-modification.
• Both mechanisms utilize enzymes that cut a specific DNA sequence of the invading virus; however, CRISPR nucleases are programmed with phage-derived spacer sequences which are integrated into the CRISPR genetic position upon infection.
• Researchers found restriction enzymes help in providing short-term defense which can be quickly overcome through methylation of the viral genome.
• Methylation is a process by which a methyl group is added to DNA and inhibits gene expression.
• Restriction enzymes can cut short DNA sequences so bacteria can utilize these DNA sequences soon after viral infection starts.
• However, few other cells acquired spacer sequences from the cleavage site which moderate a strong type II-A CRISPR-Cas immune mechanism against the methylated virus.
• This mechanism reminds us of the eukaryotic immune response in which the innate immunity provides a first short-term line of defense and also activates a second but stronger adaptive immune response.

Sources:

Maguin, P., Varble, A., Modell, J. W., & Marraffini, L. A. (2022). Cleavage of viral DNA by restriction endonucleases stimulates the type II CRISPR-Cas immune response. Molecular cell, 82(5), 907–919.e7. https://doi.org/10.1016/j.molcel.2022.01.012

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