the 5proximal hairpin of turnip yellow mosaic virus rna its role in translation and encapsidation the rna genome of turnip yellow mosaic virus tymv consists of more than 6000 nucleotides during a study of the roles of the two hairpins located in its 90nucleotide 5 untranslated region it was observed that stabilization of the 5proximal hairpin leads to a delay in the development of symptoms on plants this delay in symptom development for both locally and systemically infected leaves was found to be dependent on a change in the free energy of the hairpin caused by introduced mutations a protoplast transfection assay revealed that the accumulation of plusstrand fulllength rna and subgenomic rna as well as protein expression levels was affected by hairpin stability stabilization of this hairpin inhibited translation a model is proposed in which a destabilized 5proximal hairpin allows maximal translation of the viral proteins it is suggested that this hairpin may exist in close proximity to the 5 cap as long as its stability is low enough to enable translation however at an acidic ph the hairpin structure becomes more stable and is functionally transformed into the initiation signal for viral packaging slightly acidic conditions can be found in chloroplasts where tymv assembly is driven by a low ph generated by active photosynthesis