Keyword - Antiviral defense (KW-0051)
Protein synthesized or activated in the cell in response to viral infection, or protein with specific antiviral activity within the cell. Eukaryotic cells have an innate immune mechanism to fight viral infection, which is activated through the interferon signaling pathway or through dsRNA detection in the cytoplasm. It leads to the establishment of an antiviral cell state, which prevents virus replication or induces apoptosis. Most viruses have developed specific proteins to prevent the establishment of an antiviral state. About half of all bacteria and most archaea have a CRISPR (clustered regularly interspersed short plaindromic repeats) system of adaptive immunity to exogenous DNA. CRISPRs clusters are tandem arrays of alternating repeats and spacers, where the spacers in some cases are homologous to sequences from virus and plasmid genomes. The CRISPR arrays are transcribed, processed and in some way aid in detection and resistance to foreign DNA. In at least a few bacteria (E.coli, S.epidermidis) it seems DNA is the target, whereas in Pyrococcus furiosis it seems the CRISPR system targets RNA.