A Golden Gate-based Protocol for Assembly of Multiplexed gRNA Expression Arrays for CRISPR/Cas9

The CRISPR (clustered regularly interspaced short palindromic repeats)-associated protein 9 (Cas9) has become the most broadly used and powerful tool for genome editing. Many applications of CRISPR-Cas9 require the delivery of multiple small guide RNAs (gRNAs) into the same cell in order to achieve multiplexed gene editing or regulation. Using traditional co-transfection of single gRNA expression vectors, the likelihood of delivering several gRNAs into the same cell decreases in accordance with the number of gRNAs. Thus, we have developed a method to efficiently assemble gRNA expression cassettes (2-30 gRNAs) into one single vector using a Golden-Gate assembly method (Vad-Nielsen et al., 2016). In this protocol, we describe the detailed step-by-step instructions for assembly of the multiplexed gRNA expression array. The gRNA scaffold used in our expression array is the gRNA 1.0 system for the Cas9 protein from Streptococcus pyogenes driven by the human U6 promoter.