What is a single guide RNA?

“Single guide RNA” (a.k.a. sgRNA) is a term commonly used in prokaryotic DNA editing involving CRISPR and Cas9, which recruits the nuclease activity and confers target sequence specificity to the CRISPR-Cas9 system. It is an artificially programmed combination of two RNA molecules, trans-activating CRISPR RNA (tracrRNA) and CRISPR RNA (crRNA). The component of crRNA is a sequence with 18-20 base pairs that bind to the target DNA, while tracrRNA functions as a scaffold for the crRNA-Cas9 interaction. Multiple crRNAs can be incorporated into a crRNA array and then packaged with tracrRNA to form a sgRNA. In the CRISPR-Cas9 system, sgRNAs first bind to Cas9 and further guide the sgRNA-Cas9 complex to a specific location on the foreign DNA, where Cas9 cuts the target DNA strand with its endonuclease activity.