(a) The methodology of our approach is outlined (refer also ). (b) The targeting landscape of a sgRNA:Cas9 complex reveals that it is potentially tolerant to 1–3 mutations in its target sequences. (c) The sgRNA:Cas9 complex is also largely insensitive to point mutations, except those localized to the PAM sequence. Notably this data reveals that the predicted PAM for the S. pyogenes Cas9 is not just NGG but also NAG. (d) Introduction of 2 base mismatches significantly impairs the sgRNA:Cas9 complex activity, primarily when these are localized to the 8–10 bases nearer the 3′ end of the sgRNA target sequence (in the heat plot the target sequence positions are labeled from 1–23 starting from the 5′ end). (e) Similarly examining the TALE off-targeting data for an 18-mer TALE reveals that it can potentially tolerate 1–2 mutations in its target sequence, and fails to activate a large majority of 3 base mismatch variants in its targets. (f) The 18-mer TALE is, similar to the sgRNA:Cas9 complexes, largely insensitive to single base mismatched in its target. (g) Introduction of 2 base mismatches significantly impairs the 18-mer TALE activity. Notably we observe that TALE activity is more sensitive to mismatches nearer the 5′ end of its target sequence (in the heat plot the target sequence positions are labeled from 1–18 starting from the 5′ end). Statistical significance symbols are: *** for P<.0005/n, ** for P<.005/n, * for P<.05/n, and N.S. (Non-Significant) for P>= .05/n, where n is the number of comparisons (refer ).