We have studied the role of the U14 small nucleolar
RNA (snoRNA) in pre-rRNA methylation and processing in
Xenopus oocytes. Depletion of U14 in Xenopus
oocytes was achieved by co-injecting two nonoverlapping
antisense oligonucleotides. Focusing on the earliest precursor,
depletion experiments revealed that the U14 snoRNA is essential
for 2′-O-ribose methylation at nt 427 of the 18S
rRNA. Injection of U14-depleted oocytes with specific U14
mutant snoRNAs indicated that conserved domain B, but not
domain A, of U14 is required for the methylation reaction.
When the effect of U14 on pre-rRNA processing is assayed,
we find only modest effects on 18S rRNA levels, and no
effect on the type or accumulation of 18S precursors, suggesting
a role for U14 in a step in ribosome biogenesis other than
cleavage of the pre-rRNA. Xenopus U14 is, therefore,
a Box C/D fibrillarin-associated snoRNA that is required
for site-specific 2′-O-ribose methylation of pre-rRNA.