The effects of the sequence identity around the cognate dinucleotide deamination motif (TC) on affinity of A3A for ssDNA was determined by first testing the change in affinity for all nucleotide substitutions at −2 position (3A)-NTC-(6 A). A3A has a preference for pyrimidine over purine at −2 position (Fig. 2b) with TTC and CTC having similar affinities (90 ± 1 nM and 85 ± 1 nM respectively) compared to that of purines ATC and GTC (145 ± 2 nM and 150 ± 3 nM respectively). While not as strong as for −1 position, there is a preference for the smaller pyrimidines at position −2. Next, the effect of +1 position on affinity of A3A to TC was determined (Fig. 2c). A3A did not demonstrate a strong preference for any particular nucleotide, although disfavoring T, at the +1 position (145 ± 2 nM for background versus 209 ± 5 nM).