The effect of ultraviolet radiation on the expression of the genes of vesicular stomatitis virus (VSV) was studied in a cell-free system which executed coupled transcription and translation of the viral genes.

Incubation of the mouse l‐cell‐free system with a concentration of pppA2′p5′A2′p5′A [(2′‐5′)An] just sufficient to inhibit protein synthesis results in formation of a high‐molecular‐weight, heatlabile inhibitor and enhanced ribonuclease activity and in the rapid breakdown of (2′‐5′)An to ATP. The (2′‐5′)An‐enhanced ribonuclease activity is also unstable and in the absence of a (2′‐5′)An‐regenerating system inhibition of protein synthesis is transient. Although interferon treatment enhances the synthesis of (2′‐5′)An, the rates of degradation of (2′‐5′)An and levels of activatible nuclease are similar in extracts prepared from control or interferon‐treated cells. Interestingly, the sensitivity of different cell‐free systems to (2′‐5′)An varies with the source of the cell‐free systems and with the methods used in their preparation. There is, however, no obvious correlation between the sensitivities of the system and the rate of breakdown of (2′‐5′)An. The significance of these results is discussed in relation to a possible control function for the (2′‐5′)An system in both interferontreated and control cells.

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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 thatthe 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.

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