INTRON-MEDIATED ENHANCEMENT OF TRANSGENE EXPRESSION IN MAIZE IS A NUCLEAR, GENE-DEPENDENT PROCESS

In monocots, transgene expression can be stimulated by over two magnit udes by including an intron in the 5' untranslated region (UTR). The u nderlying mechanism is presently unknown. Inclusion of the salT intron into the 5' UTR of cat and bar genes stimulated expression of the fir st gene only, indicating that intron-mediated enhancement of expressio n (IME) is gene-dependent. Stimulation was associated with increased c at RNA levels, which did not result from a reduced cytoplasmic turnove r and were not associated with increased translation. This implies tha t IME acts in the nucleus. importantly the cytoplasmic accumulation of spliced cat transcripts, even with IME, is less than that encoded by the intronless bar gene. As the cat and bar genes were flanked by iden tical regulatory signals, and the transcripts had a similar cytoplasmi c stability, it may mean that IME rescues rather than stimulates gene expression.