Protein covalently linked to foot-and-mouth disease virus RNA

Abstract

THE RNA in picornaviruses can function directly as mRNA (ref. 1). In contrast to the great majority of cellular and virus mRNA molecules, however, a ‘cap’ structure has not been found at the 5′-end of the RNAs of polio^2,3 and encephalomyocarditis (EMC) (ref. 4) virus particles or on poliovirus specific mRNA in infected cells^2,3. The 5′-terminus of poliovirus mRNA extracted from polyribosomes was found to be pUp^2,3 but no nucleotide could be identified at the 5′-end of the RNA in virus particles. This is because a small protein is covalently linked to the 5′-terminal nucleotide of the RNA (refs 5, 6). The RNAs of EMC virus and foot-and-mouth disease virus (FMDV) contain a tract of about 100–200 cytidylic acid residues located near the 5′-end^7,8 but such a sequence was not found in poliovirus RNA (ref. 9). It was of interest, therefore, to determine whether a protein is also covalently linked to FMDV RNA and whether it is attached to the poly C tract. We show here that FMDV RNA is not capped and demonstrate the presence of a protein of molecular weight (MW) about 4,000 covalently linked to the RNA. The protein is not attached directly to the poly C tract but is probably attached to the 5′-terminus and can be removed without loss of infectivity.