Interferon, double-stranded RNA, and RNA degradation. Isolation of homogeneous pppA(2'p5'A)n-1 synthetase from Ehrlich ascites tumor cells.

pppA(2'p5'A)n-1 ((2'-5')(A)n) synthetase is one of the mediators of interferon action. On activation by double-stranded RNA, it converts ATP into (2'-5')(A)n; in turn, (2'-5')(A)n activates an endonuclease (RNase L) which cleaves single-stranded RNA. We report a simple procedure for the isolation of pure (2'-5')(A)n synthetase from interferon-treated Ehrlich ascites tumor cells. The procedure involves differential precipitation of the ribosomal salt wash fraction with ammonium sulfate and chromatography on DEAE-cellulose and CM-cellulose. The apparent molecular weight of the enzyme is 105,000 as determined by gel electrophoresis in sodium dodecyl sulfate and about 85,000 when determined by centrifugation through a glycerol gradient. The size range of the (2'-5')(A)n produced by the enzyme extends from the dimer to at least the pentadecamer.