Increased nuclease activity in cells treated with pppA2'p5'A2'p5' A.

A series of 2'-5'-linked oligo(adenylic acid) triphosphate (2'-5' A) inhibitors of protein synthesis were described recently. These inhibitors are synthesized from ATP by an enzyme activated in interferon-treated cell extracts or rabbit reticulocyte lysates by double-stranded RNA. We show here that 2'-5' A is a potent inhibitor of protein synthesis in intact cells of different origin (human, monkey, hamster, and mouse). At a concentration of 10 nM (in AMP equivalents), protein synthesis is inhibited by 50-85%. There is also a secondary effect on the total RNA synthesis which becomes evident several hours after inhibition of protein synthesis. All of these effects, however, are transient and, after a recovery period, both RNA and protein synthesis resume rates comparable to the appropriate controls. A nuclease activity is detected in cells after treatment with 2'-5'A. The total polyadenylylated RNA is much reduced in comparison to that from untreated cells, and electrophoretic analysis in polyacrylamide slab gels provides evidence for its degradation. Similarly, there is an apparent degradation of ribosomal RNA. Consistent with these results, extracts from cells that had been treated with 2'-5'A manifest an enhanced nuclease activity in vitro on incubation with exogenous RNA. Here, we propose that, as in cell-free systems, the mechanism of action of 2'-5'A in intact cells involves activation of a nuclease. This activation is transient, but the nuclease remains sensitive to further activation by the inhibitor.