Journal: Nucleic Acids Research
Article Title: Elimination of cis -cleavage in CRISPR diagnostics for one-pot rapid nucleic acid detection
doi: 10.1093/nar/gkag267
Figure Lengend Snippet: SCas12a system enables PAM- and cis- cleavage-free detection of DNA. ( a ) Schematic illustration of the SCas12a assay for detecting RNA and DNA targets. ( b ) Cis-cleavage of target dsDNA plasmids by As, Lb, and Ct Cas12a proteins, with or without a PAM sequence (TTTG). The reactions contained 100 nM Cas12a, 200 nM split crRNA, and 10 nM target dsDNA plasmids containing HPV16 target sequences. ( c ) Fluorescence-based detection of WT Cas12a’s trans-cleavage activity in the presence of target dsDNA substrates containing canonical, suboptimal, or absent PAM sequences, using a complete crRNA targeting the gene fragment of HPV16. The reactions contained 250 nM Cas12a, 500 nM crRNA, 10 nM target dsDNA substrate, and 1000 nM FAM-labeled ssDNA fluorescence probes. ( d ) Fluorescence-based detection of SCas12a system’s trans-cleavage activity in the presence of target dsDNA substrates containing canonical, suboptimal, or absent PAM sequences, using a split crRNA targeting the gene fragment of HPV16. The reactions contained 250 nM Cas12a, 500 nM crRNA, 10 nM target dsDNA substrate, and 1000 nM FAM-labeled ssDNA fluorescence probes. ( e ) Heatmap representing a comparison of the trans-cleavage activity between the SCas12a and WT Cas12a systems on identical DNA substrates with or without PAM sequences. ( f ) Detection of PAM-free dsDNA substrates by As, Lb, and Ct Cas12a proteins. The reaction mixtures were incubated for 60 min at 37°C for AsCas12a and LbCas12a, and at 55°C for CtCas12a, and contained 250 nM Cas12a, 500 nM crRNA, 10 nM target dsDNA substrate, and 1000 nM FAM-labeled ssDNA fluorescence probes. ( g ) Comparison of the maximum fluorescence values among As, Lb, and Ct Cas12a in Fig. . Mean ± s.d. of n = 3 technical replicates for panels (c–g). a.u., arbitrary units.
Article Snippet: FAM-labeled ssDNA probes, DNA and RNA oligonucleotides, and gene fragments were synthesized by Sangon Biotech (Shanghai, China).
Techniques: Sequencing, Fluorescence, Activity Assay, Labeling, Comparison, Incubation