Servizio Comunitario di Informazione in materia di Ricerca e Sviluppo - CORDIS

Control of translation of specific viral and cellular messenger ribonucleic acids in plants

The project concerns detecting and characterizing the plant cell factors involved in the preferential translation of specific messenger ribonucleic acids (mRNA). The role of untranslated regions, the leaders and trailers of several viral RNAs and a host mRNA was analysed. For tobacco mosaic virus (TMV) RNA leaders and trailers can cooperate in initiating translation. This is probably achieved by various proteins binding to these RNA regions and to other proteins. Among others, poly(A)-binding protein, polypyrimidine-binding protein, certain initiation factors and elongation factor 1a were found to bind to various non-canonical sites on TMV and other viral RNAs. Also involved in translation from the TMV RNA is a small RNA, produced upon heat shock and active in translation after heat shock. This RNA was found to correspond to the 5'-end of 18S RNA.

Leaders can be highly structured. The predicted conformation of the leader of cauliflower mosaic virus (CaMV) 35S RNA, a low energy elongated hairpin, base pairing the two halves of the leader with a cross like structure at the top, was strongly supported by enzymic probing, chemical modification and phylogenetic comparison. Higher order structures were studied with temperature gradient gel electrophoresis. These are stabilized at higher ionic strength and encompass: a long range pseudoknot connecting central and terminal parts of the leader; a dimer probably initiated by kissing loop interaction. In CaMV and other plant pararetroviruses, such a structure, in combination with a small open reading frame, allowed the transfer of ribosomes from one position of the RNA to another one located several hundred bases further downstream. This process was termed shunting. The role of the 5` leader sequence in regulating the synthesis of a plant transcription factor, Opaque-2 (O2), has been investigated. The leader sequence determined the amount of O2 protein present, a relationship which did not react to varying nutrient conditions.