In vivo aminoacylation and ‘processing’ of turnip yellow mosaic virus RNA in Xenopus laevis oocytes

Abstract

IT is now well established that several plant and animal virus RNAs possess a ‘tRNA-like’ structure, as they are recognised in vitro by many tRNA-specific enzymes. To approach the problem of the possible physiological significance of these structures for the development of the virus, it seemed important to determine whether they are also recognised in vivo. The most logical approach would have been to use plant protoplast systems to study the behaviour of viral genomes in the infected cells. However, because such systems are still difficult to control, we decided to use the oocyte system. We describe here how turnip yellow mosaic virus (TYMV) RNA, which can be aminoacylated in vitro by valine¹, was microinjected into Xenopus laevis oocytes, incubated in the presence of ³H-valine and the RNA charged in vivo analysed. We conclude that TYMV RNA, the 3′ terminal sequence of which is –CC (refs 2, 3), is amino-acylated in vivo. This indicates that the viral RNA is recognised by the oocyte tRNA nucleotidyltransferase and valyl-tRNA synthetase. Furthermore, the TYMV Val-RNA recovered after the in vivo reaction is fragmented and migrates between 4S and 5S RNA markers. This implies that (an) RNase(s) split(s) the viral genome, liberating this tRNA-like structure.