REQUIREMENT FOR INTRON-ENCODED U22 SMALL NUCLEOLAR RNA IN 18S RIBOSOMAL-RNA MATURATION

The nucleoli of vertebrate cells contain a number of small RNAs that a re generated by the processing of intron fragments of protein-coding g ene transcripts. The host gene (UHG) for intron-encoded human U22 is u nusual in that it specifies a polyadenylated but apparently noncoding RNA. Depletion of U22 from Xenopus oocytes by oligonucleotide-directed ribonuclease H targeting prevented the processing of 18S ribosomal RN A (rRNA) at both ends. The appearance of 18S rRNA was restored by inje ction of in vitro-synthesized U22 RNA. These results identify a cellul ar function for an intronencoded small RNA.