Translation of turnip yellow mosaic virus RNA in vitro: a closed and an open coat protein cistron.

Sucrose gradient centrifugation of heat-denatured RNA of turnip yellow mosaic virus permitted the isolation of five RNA classes with molecular weights ranging from 2.0 to 0.25 X 10(6). The infectivity was shown to be confined to an RNA molecule of molecular weight 2.0 X 10(6). No significant increase in infectivity was obtained by combination of the latter RNA with the RNA classes of smaller size. Translation in vitro of the RNAs of different size classes in a wheat germ cell-free system revealed that the infectious RNA (molecular weight 2.0 X 10(6) does not promote the synthesis of the coat protein of turnip yellow mosaic virus. Efficient production of this coat protein was found exclusively when the smallest RNA class (molecular weight 250,000) was used as a messenger. It is concluded that RNA molecules of turnip yellow mosaic virus of molecular weight 2.0 X 10(6) contain a closed coat protein cistron and that RNA molecules of molecular weight about 2 to 3 X 10(5) with an open coat protein cistron can be isolated from the virions

The location of coat protein and viral RNAs of alfalfa mosaic virus in infected tobacco leaves and protoplasts

The location of coat protein of alfalfa mosaic virus (AIMV) strain 425 was determined in protoplasts isolated from infected tobacco leaves and in in vitro inoculated tobacco protoplasts, using immunocytochemistry on ultrathin frozen sections labeled with colloidal gold. In infected tobacco leaves 5 days postinoculation (p.i.) coat protein is present in the cytoplasm and nucleus, especially around the nucleolus. In in vitro inoculated tobacco protoplasts coat protein was not present in the nucleus 6 hr p.i. These results indicate that the presence of coat protein in the nucleus is not necessary for viral replication. However, coat protein could be detected in the nucleus 48 hr p.i. Probably coat protein or virus particles accumulate in the nucleus late in infection. Minus-strand RNA, as part of the replication complex, could be detected in a 650 g pellet fraction of infected tobacco leaves but not in the nucleus, suggesting that replication of AIMV occurs outside the nucleus