Translational studies with turnip yellow mosaic virus RNAs isolated from major and minor virus particles

The major and minor nucleoprotein components in turnip yellow mosaic virus (TYMV) preparations have been fractionated by four cycles of CsCl gradient equilibrium centrifugations. RNAs isolated from the various fractions were translated in a rabbit reticulocyte cell-free system. Three classes of RNAs were studied: genomic RNA with an Mr of 2.0 x 10(6), the subgenomic coat protein messenger with an (r) of 2.4 x 10(5) (H. Guilley and J. P. Briand, 1978, Cell15, 113-122) and RNA molecules of intermediate sizes. Genomic RNA is found in the major TYMV components. These particles do not contain the coat protein messenger. The latter messenger has mainly been detected in two types of minor components, those which have an RNA content exceeding that of the major TYMV virions and particles which contain the coat protein messenger as their sole RNA constituent. RNAs of intermediate sizes are found in minor components less dense than the major particles; the full-length translational products of these RNAs and of genomic RNA overlap with one another and share a common NH2 terminus. It is concluded that a number of intermediate-sized RNAs and the genomic RNA have a common site for initiation of translation located close to their 5'-termini.