8-Azido-ATP is a ribonucleoside triphosphate analog with an azido group substitution at the adenine C-8 position It acts primarily as an ATP mimic interacting with poly(A) polymerase (PAP) specifically illustrated using yeast poly(A) polymerase (yPAP) Incorporation of 8-azido-ATP into growing polyadenylation chains results in premature termination and moderately shorter poly(A) tails relative to natural ATP substrates Due to its chain-terminating capacity and altered substrate specificity 8-azido-ATP is applied in biochemical studies examining enzyme fidelity nucleotide selection mechanisms and RNA polymerase activity