DOUBLE-STRANDED RNA AND 2′,5′-OLIGOADENYLATES: COMPANIONS IN INTERFERON ACTION?

A number of oligonucleotides have been synthesized and evaluated as antagonists of the protein synthesis inhibitory effects of 2-5A in order to gain information on the oligonucleotide structural features involved in binding to the 2-5A-activated endoribonuclease. The base moieties, the ribose-phosphate backbone and the 5′-monophosphate group of p5′A2′p5′A2′p5′A are strategic regions for binding to the endonuclease; however, rather extensive modification of the 2′-terminal ribose unit is possible without adversely affecting interaction with the endonuclease. Analogues of p5′A2′p5′A2′p5′A, p5′A2′p5′ A2′p5′A2′p5′A or ppp5′A2′p5′A2′p5′A2′p5′A, in which the 2′-terminal ribose has been modified to an N-hexylmorpholine ring have significantly enhanced activity as antagonists of 2-5A action or as inhibitors of protein synthesis. Such analogues are much more resistant to degradation by the phosphodiesterase activity found in L cell extracts. These analogues of p5′A2′p5′A2′p5′A are also effective antagonists of the inhibition of protein synthesis caused by dsRNA in extracts of interferon-treated L cells, and their use demonstrates that 2-5A is the primary mediator of inhibition caused by dsRNA. In accord with this finding, the synthetic dsRNA, poly(A). poly(dUfl), an activator of the protein P 1 kinase but not the 2-5A synthetase, was a potent inhibitor of protein synthesis in rabbit reticulocyte lysates, but was without discernable activity in extracts of interferon-treated L cells. Thus, phosphorylation of eIF-2α and/or protein does not appear to be a sufficient condition for protein synthesis inhibition in extracts of interferon-treated L cells.