Translational regulation of expression of the brome-mosaic-virus RNA genome in vitro.

Total brome mosaic virus (BMV) RNA, comprising four mRNA molecules, was translated in the wheat germ system. It was shown that at a low ratio of total BMV RNA to cell-free extract all four BMV genes were expressed. At a high excess of total BMV RNA over the cell-free extract, the only BMV gene translated was the coat protein cistron (RNA 4). The effect was due to diminished initiation of synthesis of non-coat proteins in the presence of a high excess of template over 23 000 X g extract. This leads to exclusion from the translational machinery of all but coat protein genes. The effect is responsible for regulation of expression of BMV genes in vitro and can be of importance for enhancement of coat protein synthesis as expected in the late phase of virus development in vivo.