In vitro inhibition of protein synthesis by purified cores from vaccinia virus.

The mechanism of the shutoff of cellular protein synthesis in vaccinia virus-infected cells has been investigated by using in vitro systems. Purified vaccinia cores cause inhibition of endogenous mRNA translation in nonpreincubated reticulocyte lysates and Ehrlich ascites tumor cell-free systems. Translation of viral mRNA from turnip yellow mosaic virus is also impaired in wheat germ cell-free extracts. The block induced by vaccinia cores in protein synthesis is not due to a decrease in the availability of mRNA but rather to an alteration of the cellular translational machinery. No nucleolytic activity able of digesting mRNA could be detected in purified vaccinia cores with three sensitive tests. There is a lack of inhibition in the poly(Phe)-poly(U) system, which bypasses the normal initiation process. An almost complete disaggregation of polyribosomes in the reticulocyte lysate appears when vaccinia cores are present. These results indicate that mRNA translation in a cell-free system is affected predominantly at the level of polypeptide chain initiation.