Oligonucleotide inhibitor of protein synthesis made in extracts of interferon-treated chick embryo cells: comparison with the mouse low molecular weight inhibitor

Abstract

Cytoplasmic extracts of interferon-treated primary chick embryo cells contain an enzyme activity that synthesized an inhibitor of chick cell-free protein synthesis. The same activity was detected in extracts of cells treated with mock preparations of interferon, but at <0.3% of the level found in interferon-treated cell extracts. The enzyme was activated by double-stranded RNA and could be isolated by binding to columns of poly(I)-poly(C)-agarose. In the column-bound state, the enzyme reacted with ATP to synthesize the inhibitor, which could then be continuously eluted from the column. The inhibitor was purified and its structure and function were compared with those of the low molecular weight inhibitor of protein synthesis made by an enzyme from interferon-treated mouse L cells. The avian and mammalian inhibitors comigrated on thin layers of polyethyleneimine-cellulose during chromatography in three different solvent systems, and they coeluted as a series of peaks from columns of DEAE-cellulose during sodium chloride gradient elution. Digestion with bacterial alkaline phosphatase or snake venom phosphodiesterase yielded products that similarly comigrated. Functionally, the two inhibitors were interchangeable: both inhibited protein synthesis in extracts of mammalian and avian cells, producing 50% inhibition at a concentration of about 0.3 nM (AMP equivalents). We conclude that the chick cell-derived oligonucleotide inhibitor has a structure that is closely related or identical to that of the inhibitor made in the mouse system, and that both preparations inhibit cell-free protein synthesis in a non-species-specific manner.