ENHANCEMENT OF TRANSLATIONAL ACTIVITY MEDIATED BY A POTYVIRAL 5'UNTRANSLATED SEQUENCE IN-VIVO BUT NOT IN-VITRO

The effect of the potato virus Y 5' untranslated region on the transla tion of heterologous reporter genes have been investigated in two diff erent plant protoplasts systems (Nicotiana tabacum and Brassica napus) and in rabbit reticulocytes lysates. In both types of plant protoplas ts, the reporter activity was found to increase 2 to 5 fold, depending on whether DNA or RNA were used compared to a control 5' untranslated sequence. The PVY 5' UTR was unable to stimulate translation of a rep orter gene in rabbit reticulocyte lysates. In all experiments, the TMV Omega' sequence, a well characterized translational enhancer, was use d as a control for activation. Its enhancing activity in protoplasts w as found to be equivalent to that of the PVY 5' UTR. In contrast, the TMV Omega' sequence resulted in a 20 fold increase of the reporter act ivity in vitro. This suggests that these 5' UTR, derived from two diff erent plant viruses, use distinct mechanisms for initiation of transla tion.