Translation by Entrapment

Abstract

MOLECULAR BIOLOGY A group of relatively obscure plant viruses captured the attention of molecular biologists some 30 years ago when it was discovered that their RNA genomes contain a 3'-terminal transfer RNA (tRNA)-like structure (TLS) that can be aminoacylated. Work by Barends et al . now reveals a fascinating role for tRNA mimicry in the viral life cycle. Studying turnip yellow mosaic virus, whose proteins are encoded within a single polycistronic messenger RNA (mRNA), they find that the TLS appears to entrap ribosomes in a manner that promotes internal initiation of protein synthesis on the mRNA. This yields a viral RNA replication polyprotein, which incorporates the TLS-bound amino acid (valine) at its N-terminus instead of the customary methionine. From the perspective of the virus, changing the efficiency of this internal initiation mechanism would not only affect the relative levels of the viral proteins, but also alter the balance between viral mRNA translation, RNA replication, and virion assembly. In a broader sense, this finding raises the intriguing possibility that the TLS is a molecular fossil of an ancient RNA world in which chimeric RNAs with properties of both tRNA and mRNA functioned as protoribosomes. — PAK Cell 112 , 123 (2003) .