Family | Experimental/in silicoevidence | Prediction |
---|---|---|
Cas1 | Metal-dependent deoxyribonuclease; a unique fold consisting of a N-terminal β strand domain and a C-terminal α-helical domain [21, 68]; also binds RNA [21, 68] | Involved in integration of spacer DNA into CRISPR repeats. |
Cas2 | RNAse specific to U-rich regions [23] | Facilitates spacer selection and/or integration. Could be involved in further crRNA cleavage. |
Cas3 (helicase and HD domain) | Single-stranded DNA nuclease (HD domain) and ATP-dependent helicase [24]; required for interference [13]. | Cuts DNA during interference; promotes strand separation. |
Stand alone HD nuclease | Metal-dependent deoxyribonuclease specific for double-stranded oligonucleotides [69]. | Cuts DNA during interference. |
Cas4 | RecB-like nuclease homolog with three-cysteine C-terminal cluster [5] | Might be involved in spacer acquisition |
Cas5 | Might substitute for Cas6 if catalytically active. Otherwise might be involved in both interference and adaptation stages. | |
Cas6 | RAMP [5]; metal-independent endoribonuclease that generates crRNAs, subunit of Cascade complex [8, 13–15, 17]. |  |
Cas7 | RAMP [5], subunit of Cascade complex [13]; present Cascade complex of I-E systems in 6 copies [8] and in several copies in I-A systems [16]. | Implicated in interference; binds crRNA; if enzymatically active, might be involved in RNA-guided RNA cleavage. |
Cas8 (large subunit) | Subunit of Cascade complex [13]. | Inactivated Cas10 polymerase-like protein, binds DNA, interacts with HD domain and a RAMP carrying crRNA; could be involved in both interference and spacer selection stages. |
Cas10 (large subunit, CRISPR polymerase) | Subunit of Cascade (Cmr) complex [15]; homologous to Palm domain polymerases and cyclases. | Same as Cas8, but fused to HD and thus cuts ssDNA; might be involved in strand separation. |
Small subunit | Small, mostly alpha helical protein, subunit of Cascade complex [13, 15]; present in Cascade complex of I-E systems in two copies [8] | Specifically binds DNA; might recognize PAM. |