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 nec rosis virus (STNV) and the plant chlorophyll a/b-binding protein (Cab2 2L), were shown to modulate the beta-glucuronidase reporter protein ac cumulation levels in transient expression experiments. The same chimer ic constructs also confer differential distribution patterns of report er protein accumulation in stably-transformed tobacco calli or regener ated transgenic plants. When the highest expression levels with a give n leader are compared, the 31-nucleotide random leader stimulates tran slation 20- and 100-fold relative to the 9- and 4-nucleotide synthetic leaders respectively. However, this 31-nucleotide random leader is ap prox. 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-nucleot ide Cab22L leader. These results confirm the findings in transient exp ression experiments and stress the importance of the 5'-untranslated r egion for the production of heterologous proteins in transgenic plants .