Cell-free protein synthesis of CRISPR ribonucleoproteins (RNP)

Cell-free protein synthesis is a powerful tool to produce recombinant proteins, and as an open system, can often integrate all or part of downstream assays. Here we describe in vitro synthesis of the Streptococcus pyogenes type II-A CRISPR-Cas9 ribonucleoproteins (SpCas9 RNPs), consisting of the effector protein and the single guide RNAs (sgRNAs). In spite of its large molecular weight (160 kDa), the SpCas9 effector is expressed relatively well from linear DNA templates under T7 promoter in commercial reconstituted cell-free protein synthesis systems. sgRNAs can be added before the effector synthesis reaction, or transcribed directly from linear DNA templates during the synthesis reaction. The newly synthesized SpCas9 effector forms an active RNP complex with sgRNAs. When a reconstituted cell-free system is used, the target DNA templates can also be added in the reactions, thereby combining CRISPR-Cas synthesis and activity assay.