Presence of Poly (A) in the Polyribosome-associated RNA of Sindbis-infected BHK Cells

Abstract

POLYNUCLEOTIDE sequences rich in adenylic acid (poly (A)) have been found in a variety of eukaryotic messenger, heterogenous nuclear (Hn) and viral RNAs^1–5. Poly (A) tracts in HeLa and ascites cell polyribosome-associated RNA sediment at 4-5S in sucrose gradients and contain 85–99% AMP^6,7. In Polyacrylamide gels, their mobility suggests a nucleotide content of 150–250 residues. Experiments using actinomycin D and cordycepin indicate that poly (A) in Hn RNA may be added after transcription⁸. Similar poly (A) sequences have been described in the early and late mRNA produced by vaccinia and adeno viruses^{9, 10}. Vaccinia DNA contains dT sequences which hybridize with poly (A) and may code for the poly (A) in vaccinia mRNA. Adeno DNA does not contain sequences which can hybridize to poly (A), and it was suggested that the poly (A) in adeno mRNA arises, not by transcription of viral DNA, but by addition of cellular poly (A) to viral mRNA in the nucleus of infected cells¹⁰. We report here the isolation of poly (A) from viral-specific polyribosomes isolated from BHK 21 cells infected with Sindbis, a group A arbovirus which replicates exclusively in the cytoplasm.