Synthesis of Plant Virus Coat Proteins in an Animal Cell-free System

Abstract

CELL-FREE systems which are capable of accurate translation of exogenous mRNA have proved invaluable tools for studying the mechanism of protein synthesis both in prokaryotes¹ and, more recently, in eukaryotes². Since the availability of suitable mRNAs is often a limiting factor in such studies, RNA-containing viruses have been widely used as sources of RNA for translation in bacterial, plant, and animal cell-free systems; for example, the bacteriophages f2 (ref. 3) and Qβ (ref. 4), the plant viruses brome mosaic virus⁵ and satellite tobacco necrosis virus⁶, and the picornaviruses, encephalomyocarditis virus⁷ and mengo virus⁸. But, although picornavirus RNA is actively translated in animal cell-free systems, it is not an ideal messenger since its large size⁹ and single polypeptide chain initiation sit^{10, 11} hinder complete translation in vitro¹². As alternative sources of mRNA for animal cell-free systems, we have studied the plant viruses brome mosaic virus (BMV) and tobacco rattle virus (TRV). Here we report the efficient and accurate synthesis of the coat proteins of these viruses in a mammalian cell-free system directed by the viral RNAs.