U14 BASE-PAIRS WITH 18S RIBOSOMAL-RNA - A NOVEL SNORNA INTERACTION REQUIRED FOR RIBOSOMAL-RNA PROCESSING

U14 is a conserved small nucleolar RNA (snoRNA) required for processin g of yeast 18S rRNA. The presence of two long sequences (13 and 14 nuc leotides) with strong complementarity to 18S rRNA suggests that U14 ba se-pairs with pre-rRNA. Evidence of direct binding was developed by sh owing that mutations in these U14 elements mimic U14 depletion and tha t function can be rescued by a compensatory sequence change in 18S RNA . The U14 elements are functionally interdependent, indicating that bo th participate in binding. folding models predict that binding might o ccur through both rRNA elements simultaneously. Potential roles of U14 in rRNA folding, maturation, and ribosome assembly are discussed. U14 is one of several snoRNAs with long complementarities to rRNA and the first snoRNA in this class shown to interact directly with rRNA.