Solution structure of conserved AGNN tetraloops: insights into Rnt1p RNA processing. |
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Authors: | I Lebars B Lamontagne S Yoshizawa S Aboul-Elela D Fourmy |
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Institution: | Laboratoire de RMN, ICSN-CNRS, 1 ave de la terrasse, F-91190 Gif-sur-Yvette, France. |
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Abstract: | Rnt1p, the yeast orthologue of RNase III, cleaves rRNAs, snRNAs and snoRNAs at a stem capped with conserved AGNN tetraloop. Here we show that 9 bp long stems ending with AGAA or AGUC tetraloops bind to Rnt1p and direct specific but sequence-independent RNA cleavage when provided with stems longer than 13 bp. The solution structures of these two tetraloops reveal a common fold for the terminal loop stabilized by non-canonical A-A or A-C pairs and extensive base stacking. The conserved nucleotides are stacked at the 5' side of the loop, exposing their Watson-Crick and Hoogsteen faces for recognition by Rnt1p. These results indicate that yeast RNase III recognizes the fold of a conserved single-stranded tetraloop to direct specific dsRNA cleavage. |
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