Viral messenger RNA unmethylated in the 5'-terminal guanosine in interferon-treated HeLa cells infected with vesicular stomatitis virus

The distribution of viral mRNA between polysomal and nonpolysomal fractions was investigated in interferon-treated cells infected with vesicular stomatitis virus (VSV). More than half of the viral mRNA synthesized by these cells is in the nonpolysomal fraction, whereas less than one-third of the mRNA synthesized by control cells is found in this fraction. Polysomal and nonpolysomal mRNA sediment identically on sucrose density gradients, but the nonpolysomal mRNA from interferon-treated cells in under-methylated, as shown by labeling experiments with [methyl-³H]methionine. Analysis of VSV mRNA after digestion with nucleases shows that all molecules are capped but about 60% of the nonpolysomal mRNA isolated from interferon-treated cells is unmethylated in the 5′-terminal G. When tested in an assay for initiation of protein synthesis, only 45% of this mRNA binds to ribosomes, as compared to 80% binding for polysomal mRNA from either control or interferon-treated cells.