Marie-Dominique Morch

Stop making sense: or regulation at the level of termination in eukaryotic protein synthesis

An increasing number of examples of translational regulation at the level of termination has been recently reported in eukaryotes. This paper reviews our present knowledge on this topic and proposes an understanding of these regulations by relating the study of viral gene expression to a comprehensive view of the mechanisms and components of the translational process.

Plant viruses and new perspectives in cross-protection

Cross-protection in plants is the phenomenon whereby a plant preinoculated with a mild virus strain becomes resistant to subsequent inoculation by a related severe strain. It has been used on a large scale in cases where no resistant plants are available. Although several hypotheses have been proposed to explain the molecular mechanism underlying cross-protection, no single hypothesis can account for all the data obtained. Recently, a phenomenon akin to cross-protection has been achieved in transformed plants harboring the cDNA of a part of a viral RNA genome. These results obtained by genetic engineering raise new hopes for obtaining plants resistant to virus infection.

Comparison of three different cell-free systems for turnip yellow mosaic virus RNA translation

The two proteins of molecular weights 150,000 and 195,000 specific of turnip yellow mosaic virus (TYMV) RNA translation in reticulocyte lysates have now also been detected in two other cell-free systems programmed with TYMV RNA: the wheat germ extract and the Ehrlich ascites cell-free system. The wheat germ extract contains proteases that affect the nascent TYMV polypeptide chains. The specific post-translational maturation of the protein of molecular weight 195,000 known to occur in the reticulocyte lysate has been investigated in the ascites system. An N-terminal fragment and a C-terminal fragment of molecular weights 120,000 and 78,000, respectively, could be detected co-migrating with the post-translational cleavage products observed in the reticulocyte lysate. Similarly, a C-terminally labelled 78,000 molecular weight fragment could be observed in the wheat germ system. The differences between the three in vitro systems with respect to TYMV RNA translation are discussed.

Regulation of Translation of Viral mRNAs

Translation constitutes a crucial step in virus development, since it leads to the production of the structural and nonstructural proteins required by the virus. Because of their relative simplicity, viral genomes, and in particular viral RNA genomes, have served as model systems to investigate the steps involved in protein synthesis and have successfully helped to unravel the various strategies of translation known to occur on mRNA templates.

Can Plant RNA Viruses Exchange Genetic Material

The problem of the exchange of genetic material among viruses is intimately related to that of the evolution of these viruses, as are also the acquisition or the loss of genetic material. Similarly, the concept of virus evolution is associated with that of the origin of viruses.