a. The reaction scheme shows the relevant region of the primer and template and two possible outcomes of the primer elongation. Elongation of the primer in the presence of dGTP or ACV-TP is indicated by the “Z” in red, which refers to the incorporated monophosphate dGMP or ACV-MP, respectively. Incorporation events following position “Z” with dTTP are in blue underlined.
b. The primer (S, lane C) was initially elongated to incorporate dGMP or ACV-MP, respectively at the 3’-end referred to as “Z”. Incubation with increasing concentrations of the next nucleotide dTTP resulted in three nucleotide incorporation events with the dGMP terminated primer, that are labeled as products (P). Note that the ACV-MP terminated primer is not extended, which shows that the inhibitor acts as a chain-terminator.