CRISPR (clustered regularly interspaced short palindromic repeat), is an adaptive immune system that provides protection against mobile genetic elements (viruses, transposable elements and conjugative plasmids). CRISPR clusters contain sequences complementary to antecedent mobile elements and target invading nucleic acids. CRISPR clusters are transcribed and processed into CRISPR RNA (crRNA). Recognizes a short motif in the CRISPR repeat sequences (the 5' PAM or protospacer adjacent motif, TTTN in this organism) to help distinguish self versus nonself, as targets within the bacterial CRISPR locus do not have PAMs (PubMed:26422227). Has dsDNA endonuclease activity, results in staggered 4-base 5' overhangs 19 and 22 bases downstream of the PAM on the non-targeted and targeted strand respectively (PubMed:26422227). Non-target strand cleavage by the RuvC domain is probably a prerequisite of target strand cleavage by the Nuc domain (PubMed:27114038). In this CRISPR system correct processing of pre-crRNA requires only this protein and the CRISPR locus (By similarity). Endonucleolytic cleavage to 5'-phosphodinucleotide and 5'-phosphooligonucleotide end-products. RNA = a 5'-hydroxy-ribonucleotide + n nucleoside-2',3'-cyclophosphates. Monomer (PubMed:27114038). Has a bilobed structure, with the REC lobe (residues 35-526) connected to the NUC lobe (residues 1-35 and 526-1307) by a discontinuous wedge domain (PubMed:27114038, PubMed:27444870). The crRNA-target DNA heteroduplex is bound in the channel between the 2 lobes (PubMed:27114038, PubMed:27444870). One nuclease site is found in the discontinuous RuvC domain which probably cuts target DNA strand in the crRNA-DNA heteroduplex (residues 884-940, 957-1066 and 1262-1307), the other in the NUC domain and probably cuts the non-target DNA strand outside the heteroduplex (residues 1067-1261) (PubMed:27114038). Target DNA binding induces domain movement (PubMed:27444870). This class of CRISPR enzymes recognize a 5' T-rich protospacer adjacent motif (PAM, TTTN for this specific enzyme), unlike Cas9 enzymes which recognize 3' G-rich PAMs, thus this enzyme increases the possibilites for genome editing (PubMed:26422227). When appropriately expressed in a human cell line mediates human genome editing via indel formation; its T-rich PAM sequence may make it useful for engineering of AT-rich genomes or of regions such as scaffold-matrix attachment areas (PubMed:26422227, PubMed:27347757). It has also been engineered to recognize altered PAM sequences, which will enlarge its target scope (PubMed:28595896). Part of a type V-A CRISPR-Cas system. Belongs to the CRISPR-associated endonuclease Cas12a family.