A poly(U) motif in the 5′ untranslated region enhances the translational efficiency of β-glucuronidase mRNA in transgenic tobacco

We examined how the base composition of the 5' untranslated region (UTR) modifies the translational efficiency of plant mRNAs with the aid of chimeric reporter constructs, and transient and stable transformation of tobacco. We inserted 20 base homopolymers of G, A. T and C into the 5' UTR of a beta-glucuronidase (GUS) reporter gene driven by the cauliflower mosaic virus 35S promoter, and the resultant constructs were introduced into tobacco seedlings by particle bombardment. The transient GUS activity of the seedlings became higher only when the (T)(20) Motif was inserted. To elucidate how the (T)(20) motif altered gene expression, we introduced the (T)(20)-inserted GUS construct into tobacco plants by Agrobacterium-mediated stable transformation and examined its expression in comparison with the GUS construct with no insert. The apparent GUS activity of the (T)(20)-GUS transgenic plants was 4.5-fold higher than that of the control GUS transformants, although the GUS mRNA levels were similar between these transgenic lines. The GUS activity/GUS mRNA ratio was 5.6-fold higher in the (T)20-inserted GUS transformants than in the controls. This indicates that the (U)(20) Motif inserted into the 5' UTR enhances the translational efficiency of the GUS reporter mRNA in tobacco cells. (C) 2003 Elsevier Ireland Ltd. All rights reserved.