Microbial warfare against viruses

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Science  02 Mar 2018:
Vol. 359, Issue 6379, pp. 993
DOI: 10.1126/science.aas9430

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Immune systems are divided into two types: innate and adaptive immunity. The innate immune system consists of components that are present in host organisms before infection by a pathogen and provides the first line of defense. For example, the restriction endonuclease system in prokaryotes degrades invader DNA (1). The adaptive immune system is activated after infection and provides immunological memory and long-lasting protection against the same pathogen. The CRISPR system captures a small piece of foreign DNA as a memory and recognizes and cleaves the same foreign DNA on reexposure (2), serving as adaptive immunity in prokaryotes. On page 1008 of this issue, Doron et al. (3) unveil previously unknown immune systems in bacteria and archaea against invading genetic elements, including plasmid DNA and bacteriophages (viruses that infect bacteria). Some of these systems may provide powerful tools for biomedical research and biotechnology, like restriction endonucleases and CRISPR.