AsCas12a (previously AsCpf1) was characterized as an RNA-guided endonuclease capable of efficient mammalian genome-editing activity in 2015. And it has subsequently become a staple in the CRISPR toolbox. Recognizing a thymine-rich 5'-TTTV-3' PAM on the 5' side of the protospacer (on the non-target strand), AsCas12a utilizes a single catalytic site to cleave RNA-complementary double-stranded DNA (cis cleavage), as well as indiscriminately cleave single-stranded DNA (trans cleavage), upon RNA-guided DNA binding. This has led to its use in rapid and highly sensitive nucleic acid detection. AsCas12a and related orthologs LbCas12a and FnCas12a generate staggered cuts within the protospacer but distal to the PAM. Because AsCas12a does not require tracrRNA and can process the CRISPR array into crRNAs internally, it is a good tool for multiplex editing.
