Yeast Rrp9p is an evolutionarily conserved U3 snoRNP protein essential for early pre-rRNA processing cleavages and requires box C for its association

摘要

Pre-rRNA processing in eukaryotic cells requires participation of several snoRNPs, These include the highly conserved and abundant Us snoRNP, which is essential far synthesis of 18S rRNA. Here we report the characterization of Rrp9p, a novel yeast Us protein, identified via its homology to the human U3-55k protein, Epitope-tagged Rrp9p specifically precipitates Us snoRNA, but Rrp9p is not required for the stable accumulation of this snoRNA, Genetic depletion of Rrp9p inhibits the early cleavages of the primary pre-rRNA transcript at A(0), A(1), and A(2) and, consequently, production of 18S, but not 25S and 5.8S, rRNA, The hU3-55k protein can partially complement a yeast rrp9 null mutant, indicating that the function of this protein has been conserved. Immunoprecipitation of extracts from cells that coexpress epitope-tagged Rrp9p and various mutant forms of Us snoRNA limits the region required for association of Rrp9p to the Us-specific box B/C motif, Box C is essential, whereas box B plays a supportive role. [References: 53]