Methylation of vaccinia virus-specific mRNA in the interferon-treated chick cell☆

Abstract Results obtained with cell-free protein-synthesizing systems imply a mediating role of the methylated 5′-terminal “cap” structure in the regulation of poxvirus-specific protein synthesis. In order to study a possible involvement of methylation in the interferon-induced inhibition of virus-specific protein synthesis in Vaccinia-infected cells, the extent of methylation of Vaccinia mRNA synthesized in interferon-pretreated and control chick embryo fibroblasts was compared. Induction of the antiviral state by pretreatment of chick cells with homologous interferon does not markedly reduce the degree of overall methylation of virus-specific mRNAs. Besides the two predominant “cap I” structures m 7 GpppAmpN and m 7 GpppGmpN, “incomplete” structures m 7 GpppA and m 7 GpppG can be detected in Vaccinia mRNA isolated from interferon-treated as well as from control cells. The ratio of complete to incomplete “cap I” structures is decreased in the viral RNA from interferon-treated cells. This qualitative change in “cap” methylation seems not to be limited to virus-specific mRNA. Possible implications of these findings on translational control in the interferon-treated cell are discussed.