DIFFERENT 5'-LEADER SEQUENCES MODULATE BETA-GLUCURONIDASE ACCUMULATION LEVELS IN TRANSGENIC NICOTIANA-TABACUM PLANTS

Three random synthetic leaders and three naturally-occurring leaders, the tobacco mosaic virus (TMV) coat protein, the satellite tobacco necrosis virus (STNV) and the plant chlorophyll a/b-binding protein (Cab22L), were shown to modulate the beta-glucuronidase reporter protein accumulation levels in transient expression experiments. The same chimeric constructs also confer differential distribution patterns of reporter protein accumulation in stably-transformed tobacco calli or regenerated transgenic plants. When the highest expression levels with a given leader are compared, the 31-nucleotide random leader stimulates translation 20- and 100-fold relative to the 9- and 4-nucleotide synthetic leaders respectively. However, this 31-nucleotide random leader is approx. 2 to 3-fold weaker than the 30-nucleotide STNV leader and even 5-fold weaker than both the 79-nucleotide TMV leader and the 66-nucleotide Cab22L leader. These results confirm the findings in transient expression experiments and stress the importance of the 5'-untranslated region for the production of heterologous proteins in transgenic plants.