Since the adaptation module in M. mazei seems to be repressed under standard growth conditions with no detectable Cas1, Cas2 and Cas4 proteins [27], and no MetSV-derived spacers were detectable after virus infection [26], we analyzed the ability of MM_0565 to bind to the leader region of the corresponding CRISPR-array, which contains important elements for the acquisition of new spacers into the CRISPR array [56,57,58,59]. Here, CASS4 is linked to viral infectious disease.