Tige-boucle

Résumé

thumb|right|Structure en tige et boucle formée par une séquence répétée inversée sur l'ARN. Une tige-boucle (ou "structure en tige et boucle"), également connue sous le nom de structure en épingle à cheveux, est une structure intramoléculaire qui se forme sur un brin d'acide nucléique. On les trouve principalement dans l'ARN, qui existe principalement sous forme simple-brin dans les cellules. Elle se forme lorsque deux régions de la même molécule contenant des séquences répétées inversées de bases complémentaires s'apparient pour former localement une structure en double hélice. Par exemple, si l'ARN contient les deux séquences suivantes : --GUGCCACG----CGUGGCAC--, celles-ci forment un motif répété inversé, les nucléotides du second segment étant les complémentaires de ceux du premier, après inversion de leur sens de lecture. Ces deux segments peuvent donc s'apparier de manière antiparallèle pour former une région localement en double-hélice. La région entre les deux segments forme alo

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https://fr.wikipedia.org/wiki/Tige-boucle

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Regulation of mRNA stability by RNA-protein interactions contributes significantly to quantitative aspects of gene expression. We have identified potential mRNA targets of the AU-rich element binding protein AUF1. Myc-tagged AUF1 p42 was induced in mouse NIH/3T3 cells and RNA-protein complexes isolated using anti-myc tag antibody beads. Bound mRNAs were analyzed with Affymetrix microarrays. We have identified 508 potential target mRNAs that were at least 3-fold enriched compared to control cells without myc-AUF1. 22.3% of the enriched mRNAs had an AU-rich cluster in the ARED Organism database, against 16.3% of non-enriched control mRNAs. The enrichment towards AU-rich elements was also visible by AREScore with an average value of 5.2 in the enriched mRNAs versus 4.2 in the control group. Yet, numerous mRNAs were enriched without a high ARE score. The enrichment of tetrameric and pentameric sequences suggests a broad AUF1 p42-binding spectrum at short U-rich sequences flanked by A or G. Still, some enriched mRNAs were highly unstable, as those of TNFSF11 (known as RANKL), KLF10, HES1, CCNT2, SMAD6, and BCL6. We have mapped some of the instability determinants. HES1 mRNA appeared to have a coding region determinant. Detailed analysis of the RANKL and BCL6 3'UTR revealed for both that full instability required two elements, which are conserved in evolution. In RANKL mRNA both elements are AU-rich and separated by 30 bases, while in BCL6 mRNA one is AU-rich and 60 bases from a non AU-rich element that potentially forms a stem-loop structure.

PUBLIC LIBRARY SCIENCE2018

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Destabilization of interleukin-6 mRNA requires a putative RNA stem-loop structure, an AU-rich element, and the RNA-binding protein AUF1

Barbara Grisoni-Neupert, Lukas Kühn

Interleukin-6 mRNA is unstable and degraded with a half-life of 30 min. Instability determinants can entirely be attributed to the 3' untranslated region. By grafting segments of this region to stable green fluorescent protein mRNA and subsequent scanning mutagenesis, we have identified two conserved elements, which together account for most of the instability. The first corresponds to a short noncanonical AU-rich element. The other, 80 nucleotides further 5', comprises a sequence predicted to form a stem-loop structure. Neither element alone was sufficient to confer full instability, suggesting that they might cooperate. Overexpression of myc-tagged AUF1 p37 and p42 isoforms as well as suppression of endogenous AUF1 by RNA interference stabilized interleukin-6 mRNA. Both effects required the AU-rich instability element. Similarly, the proteasome inhibitor MG132 stabilized interleukin-6 mRNA probably through an increase of AUF1 levels. The mRNA coimmunoprecipitated specifically with myc-tagged AUF1 p37 and p42 in cell extracts but only when the AU-rich instability element was present. These results indicate that AUF1 binds to the AU-rich element in vivo and promotes IL-6 mRNA degradation.

2006

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Expression of the human transferrin receptor (hTR) and its mRNA is strongly induced by iron deprivation. By measuring transcription elongation rates, levels of hTR-specific nuclear RNA, and mRNA half-lives, we found this regulation to occur posttranscriptionally in the cytoplasm. Analysis of hTR cDNA mutants with deletions in the 3' untranslated region revealed the existence of two distinct domains, both of which are essential for regulation in mouse L cells. The regulated phenotype correlates with the presence of a stem-loop structure predicted by a computer algorithm. Expression of point and deletion mutants affecting the stem-loop confirmed the requirement for this secondary structure in regulation. The 3' untranslated region of hTR cDNA was sufficient to confer iron-dependent regulation on another gene.

1988

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