Analysis of the role of 5' and 3' flanking sequence elements upon in vivo expression of the plant tRNATrp genes.

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We have isolated the majority (seven) of the tRNA(Trp) genes of Arabidopsis and have studied the 5' and 3' flanking sequence requirements for their efficient expression in vivo by using an assay requiring translational suppression of the luciferase reporter gene. The expressed tRNA(Trp) genes contain no highly conserved 5' flanking sequences; however, these sequences are distinctly AT rich, contain several possible TATA elements, and are bound in vitro by recombinant plant TATA binding protein. Replacement of the natural 5' flanking sequences with three different sequences lacking TATA elements reduced expression in vivo up to 10-fold; the same effect was observed when the TATA elements of the natural 5' sequences were inactivated by point mutations. Introduction of a single TATA element from the adenovirus major late promoter into an artificial 5' flanking region of the tRNA(Trp) gene enhanced expression in vivo when the TATA element was placed at position -32 relative to the first nucleotide of the mature tRNA sequence, but not when it was placed at position -24. Primer extension analyses of in vitro transcripts revealed that the position of the TATA element helps dictate the start site of transcription. Efficient expression of the tRNA genes in vivo also required 3' flanking sequences capable of terminating transcription.

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