Figure 4.

Mutational activity of A3G tyrosine mutants is diminished, especially the Y315A mutant. Mutational activity of A3G mutants due to the expression of cytidine deaminases in E. coli was determined by using a bacterial reverse rifampicin resistance reporter assay (β-subunit of RNA polymerase) (51, 53). Mutational frequency for each WT or mutant A3G strain was calculated as the number of rifampicin-resistant colonies per 10⁸ of viable cells after making correction for the number of colonies on control plates and shown as scatter diagrams with the median value drawn through (red lines). Each experiment was repeated four times. Bacterial strains tested were vector (vector alone); wild type (wild-type A3G); Y181A/Y182A (A3G with double Y181A and Y182A mutations); Y181A (A3G with a single Y181A mutation); Y182A (A3G with a single Y182A mutation); Y315A (A3G with a single Y315A mutation); Y181A/Y182A/Y315A (A3G with a triple Y181A, Y182A, and Y315A mutations).