U17/snR30 Is a Ubiquitous snoRNA with Two Conserved Sequence Motifs Essential for 18S rRNA Production

Abstract

Saccharomyces cerevisiae snR30 is an essential box H/ACA small nucleolar RNA (snoRNA) required for the processing of 18S rRNA. Here, we show that the previously characterized human, reptilian, amphibian, and fish U17 snoRNAs represent the vertebrate homologues of yeast snR30. We also demonstrate that U17/snR30 is present in the fission yeast Schizosaccharomyces pombe and the unicellular ciliated protozoan Tetrahymena thermophila. Evolutionary comparison revealed that the 3′-terminal hairpins of U17/snR30 snoRNAs contain two highly conserved sequence motifs, the m1 (AUAUUCCUA) and m2 (AAACCAU) elements. Mutation analysis of yeast snR30 demonstrated that the m1 and m2 elements are essential for early cleavages of the 35S pre-rRNA and, consequently, for the production of mature 18S rRNA. The m1 and m2 motifs occupy the opposite strands of an internal loop structure, and they are located invariantly 7 nucleotides upstream from the ACA box of U17/snR30 snoRNAs. U17/snR30 is the first identified box H/ACA snoRNA that possesses an evolutionarily conserved role in the nucleolytic processing of eukaryotic pre-rRNA.

We thank Y. de Préval for synthesis of oligonucleotides. We are grateful to D. Tollervey, J.-P. Gélugne, and K. Collins for providing us with yeast strains D190 and 578.SC and Tetrahymena cellular RNA, respectively. We thank Y. Henry and J.-P. Gélugne for helpful discussions.

V.A. was funded by the Deutscher Akademischer Austauschdienst and Fondation pour la Recherche Médicale. P.F. was funded by CNR-NATO and CNRS. Our work was supported by grants from la Ligue Nationale contre le Cancer, Association pour le Recherche contre le Cancer, and MURST (RBNE015MPB and RBNE01KXC9).