Therefore, once a bacteria survives a virus infection, it integrates the viral DNA in its genome, creating thus a registry of all past infections. This DNA is used not only to protect the bacteria from new infections, but it is passed on to new generations, by which new bacteria are automatically “vaccinated” against those viruses. The question was how these CRISPR segments led to viral immunity in bacteria. A second player was then discovered, a series of proteins associated to CRISPR (Cas), which are able to cleave DNA. These CRISPR/Cas complexes are the enforcing arm in this immune system, whereby CRISPR signals the position and Cas cuts out the foreign DNA.
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