Figure 1.

The kinetic scheme for the three-state nucleotide addition cycle (NAC) with selection. Since the cognate (right) and non-cognate (wrong) nucleotide species are differentiated in the substrate state III, one splits the cycle into two pathways for the right and wrong substrate species. Correspondingly, one has a population vector $\Pi ={\left(P_I,P_{II},P_{III}^r,P_{III}^w\right)}^T$ to describe the overall state probability distributions.