Fig. 5: Hypothesized model of the inclusion of new phages in the CRISPR memory of a bacterial cell.
From: The coordination of anti-phage immunity mechanisms in bacterial cells
The detection of a phage infection in a bacterial cell up-regulates restriction nucleases that cleave the viral DNA at specific restriction sites, fostering its subsequent digestion by other bacterial enzymes (A). Our model assumes that Cas enzymes are activated in the late stages of the innate response of the bacterial host to the infection (B), once the viral DNA has already undergone a certain degree of nuclease-mediated degradation (C). New spacers against the infecting phage can only be created by the host cell if fragments of its DNA are still present in its cytoplasm after the formation of Cas1-Cas2 complexes (D). Otherwise, Cas nucleases have no substrate to act, which prevents the incorporation of the phage into the CRISPR array of the bacterial cell (E).
