Translation Required for Translational Repression

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Science Signaling  21 Jul 2009:
Vol. 2, Issue 80, pp. ec249
DOI: 10.1126/scisignal.280ec249

Plants respond to changes in sugar concentrations by altering their transcriptional profile and their metabolic processes. Sucrose triggers the translational repression of the transcription factor bZIP11 in Arabidopsis thaliana. Rahmani et al. show that this repression requires the 5′-leader sequence of bZIP11, which, when transferred to a reporter gene, decreased the expression of the reporter gene product (luciferase) in response to sucrose, consistent with sugar-induced translational repression. Deletion analysis revealed that the second upstream open reading frame (uORF2) was required. When the mRNA sequence of uORF2 was mutated without affecting the encoded peptide, sugar-induced translational repression occurred. Transplantation of the 82 nucleotides of the uORF2 sequence into the promoter of a gene not normally regulated by sucrose caused the production of the reporter gene to decrease in response to sucrose. Mutation of the encoded peptide, or changing the length of the encoded peptide, or inserting a frameshift mutation to alter the sequence of the encoded peptide abolished the decrease in reporter gene expression in response to sucrose. The authors propose that the ribosome initiates translation inefficiently at the uORF2 and then dissociates, thus preventing translation of bZIPII, and that bZIP11 is produced by leaky scanning of the promoter by the ribosome. Indeed, production of the reporter gene was notably diminished under basal conditions and further inhibited in response to sucrose when the uORF2 start codon sequence was optimized, but reporter gene production was unaffected by mutation of a gene required for ribosome reinitiation. The authors suggest that sucrose triggers an interaction of the uORF2-encoded peptide with the ribosome, thereby stalling the ribosome and preventing translation. The mechanism by which sucrose mediates this uORF2-mediated ribosome stalling remains unknown.

F. Rahmani, M. Hummel, J. Schuurmans, A. Wiese-Klinkenberg, S. Smeekens, J. Hanson, Sucrose control of translation mediated by an upstream open reading frame-encoded peptide. Plant Physiol. 150, 1356–1367 (2009). [PubMed]

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