Description:
The biological role of Ap3A synthesized in cells by tryptophanyl‐tRNA synthetase (WRS) is unknown. Previously we have demonstrated that the cellular level of Ap3A significantly increases after interferon treatment. Here we show that the human 46 kDa 2‐5A synthetase efficiently utilizes Ap3A as a primer for oligoadenylate synthesis. The Km for Ap3A is several‐fold lower than for Ap4A and 100‐fold lower than for ATP. This implies that Ap3A might be a natural primer for the 2′‐adenylation reaction catalysed by 2‐5A synthetase. Since WRS and 2‐5A synthetase are both interferon‐inducible proteins, a new link between two interferon‐dependent enzymes is established.