Translational strategies in potexviruses: Products encoded by clover yellow mosaic virus, foxtail mosaic virus, and viola mottle virus RNAs in vitro

Abstract

We have examined the template properties of the genomic RNAs from three potexviruses: clover yellow mosaic virus (CYMV), foxtail mosaic virus (FMV), and viola mottle virus (VMV). All three RNAs encode a large (160,000 to 182,000 molecular weight) nonstructural protein when translated in the rabbit reticulocyte cell-free system. Only CYMV RNA is able to direct the synthesis of significant quantities of a product whose electrophoretic mobility, antigenic determinants, and partial peptide map resemble those of authentic coat protein. All three viral RNAs also encode a number of discrete polypeptide products whose molecular weights are intermediate between those of the large nonstructural proteins and those of their respective coat proteins. We have examined the kinetics of synthesis in vitro of these intermediate products. For each of the three viral templates, as well as for papaya mosaic virus RNA, pulse-chase experiments suggest that most, if not all, the intermediate polypeptides are incomplete (“paused”) or prematurely terminated precursors to the corresponding large nonstructural protein. A partial proteolytic map of the in vitro products encoded by CYMV RNA supports this interpretation. Our data, and those of others, are consistent with a model in which all potexviruses would encode a large nonstructural protein.