pppA2'p5'A2'p5'A: An inhibitor of i with an enzyme fraction from intei

A low molecular weight inhibitor of cell-free protein synthesis effective at subnanomolar concentrations is formed on incubation of cytoplasmic extracts from interferon- treated cells with double-stranded RNA and ATP. It can be conveniently synthesized by incubating a poly(I)*poly(C)- Sepharose-bound enzyme fraction from such cells with (3H)- or (a- or y-32P)ATP. The radioactive inhibitor has been charac- terized by its behavior on DEAE-Sephadex in the presence of urea and on the basis of the products obtained on enzymic, al- kaline, and sequential degradation by periodate oxidation and 3 elimination. Its structure appears to be pppA2'p5'A2'p5'A. We have found no evidence for any modification or abnormality other than the 2'-5' linkage. On occasion the inhibitor prepara- tions have included what seems to be the corresponding dimer (pppA2'p5'A), tetramer (ppp(A2'p)3A), pentamer (ppp(A2'p)4A), and higher oligomers in decreasing amounts. The trimer, tet- ramer, and pentamer are similar in activity, but the dimer is less potent if active at all.