Table 1: Key conserved Cas proteins and their function.

Cas protein	Function
Cas 1	Specifically exhibits nuclease activity against single stranded and branched DNA, replication forks, and may be implicated in addition of novel repeats and/or spacers.
Cas 2	Involved in novel spacer acquisition, novel repeat synthesis and repeat-spacer insertion at the leader end.
Cas3 (signature gene for type I)	Encodes a nuclease involved in the cleavage of the target DNA so responsible for the processing of crRNA and involved in recognition of target DNA.
Cas 6 (key protein for type Ι)	An endoribonuclease which cleaves the pre-crRNA within the CRISPR repeat sequence during the crRNA maturation process.
Cas 9 (signature gene for type ΙΙ)	Encodes a large protein involved in both crRNA biogenesis and target DNA cleavage.
Cas 10 (signature gene for type III)	Encodes a nuclease implicated in target nucleic acid interference.