Encephalomyocarditis virus RNA. II. Polyadenylic acid requirement for efficient translation

Differentially polyadenylated subpopulatons of encephalomyocarditis (EMC) viral RNA were isolated by affinity chromatography on oligodeoxythymidylic acid-cellulose. Translation of these RNA fractions in several in vitro protein-synthesizing systems, isolated from Ehrlich ascites tumor cells, demonstrated that poly(A)+EMC viral RNA was translated two to three times more efficiently than poly(A)-EMC viral RNA. Sodium dodecyl sulfate-polyacrylamide gel electrophoretic analysis of the polypetides synthesized by the in vitro system in response to the different RNAs showed no detectable differences in the size or relative amount- of the translational products. mRNA saturation curves indicated that the in vitro systems were stimulated maximally by equivalent amounts of RNA, wheter it be poly(A)-or poly(A)+ EMC viral RNA. Time course experiments showed that the differences in translatability were more pronounced late in the reaction when reinitiation was required, and that by eliminating reinitiation with high salt the apparent effect of poly(A) on translation was diminished. Together, these results suggest that poly(A) may be required for efficient initiation and reinitiation of protein synthesis in the cell-free systems. This interpretation is discussed relative to earlier data.