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). Has endonuclease activity on pre-crRNA and dsDNA, using different active sites. A single-RNA guided endonuclease that is also capable of guiding crRNA processing; correct processing of pre-crRNA requires only this protein and the CRISPR locus (PubMed:26422227, PubMed:27096362). pre-crRNA processing proceeds by an intramolecular nucleophilic attack on the scissile phosphate by the 2'-OH of the upstream ribonucleotide, the divalent cation (which is bound by the crRNA) is probably required for ordering the crRNA pseudoknot and/or increasing RNA binding (PubMed:28431230). RNA mutagenesis studies show pre-crRNA cleavage is highly sequence- and structure-specific (PubMed:27096362). Forms a complex with crRNA and complementary dsDNA, where the crRNA displaces the non-target DNA strand and directs endonucleolytic cleavage of both strands of the DNA (PubMed:26422227, PubMed:27096362, PubMed:28431230). Cleavage results in staggered 5-base 5' overhangs 14-18 and 21-23 bases downstream of the PAM (protospacer adjacent motif) on the non-target and target strands respectively (PubMed:26422227, PubMed:28431230, PubMed:28562584). Both target and non-target strand DNA are probably independently cleaved in the same active site (PubMed:28431230, PubMed:28562584). When this protein is expressed in E.coli it prevents plasmids homologous to the first CRISPR spacer from transforming, formally showing it is responsible for plasmid immunity (PubMed:26422227). Endonucleolytic cleavage to 5'-phosphodinucleotide and 5'-phosphooligonucleotide end-products. RNA = a 5'-hydroxy-ribonucleotide + n nucleoside-2',3'-cyclophosphates. Cleavage of dsDNA requires Mg(2+) (PubMed:26422227, PubMed:28562584). Another report shows DNA cleavage occurs equally well in the presence of Ca(2+) or Mg(2+) (PubMed:27096362). Processing of pre-crRNA requires a divalent cation, preferably Mg(2+) which is bound by the crRNA (PubMed:26593719, PubMed:28431230). Might be a homodimer (PubMed:26422227). Might be a monomer (PubMed:27096362, PubMed:28431230). Has bilobed structure, with the REC lobe (residues 25-591) connected to the NUC lobe (662-1300) by a discontinuous wedge domain (PubMed:28431230, PubMed:28562584). The REC lobe binds the (pre-)crRNA and the crRNA-target DNA heteroduplex (PubMed:28431230, PubMed:28562584). The heteroduplex as well as part of the DNA downstream of the heteroduplex is protected in the central cavity formed by the NUC and REC lobes, which also positions target and non-target DNA for cleavage after domain rearrangement (PubMed:28431230, PubMed:28562584). The LKL region (residues 662 to 679) inserts into target dsDNA initiating its disruption to allow crRNA hybridization, is also involved in determining the non-target strand cleavage site (PubMed:28562584). A 'septum' formed by residues 197-204 and 1061-1070 separates the 2 DNA strands, preventing their reannealing, this region also influences the non-target cleavage site (PubMed:28562584). This class of CRISPR enzymes recognize a 5' T-rich protospacer adjacent motif (PAM, TTN for this specific enzyme), unlike Cas9 enzymes which recognize 3' G-rich PAMs, thus this enzyme increases the possibilites for genome editing (PubMed:26422227). The simplicity of the Cas12a-crRNA directed DNA endonuclease activity has been used to target and modify DNA sequences in rice and tobacco (PubMed:27905529). Part of a type V-A CRISPR-Cas system. Belongs to the CRISPR-associated endonuclease Cas12a family.