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Mol. Cell. Biol., 07 1997, 3702-3713, Vol 17, No. 7
BA Peculis
Ribosome biogenesis in eucaryotes involves many small nucleolar
ribonucleoprotein particles (snoRNP), a few of which are essential for
processing pre-rRNA. Previously, U8 snoRNA was shown to play a critical
role in pre-rRNA processing, being essential for accumulation of mature 28S
and 5.8S rRNAs. Here, evidence which identifies a functional site of
interaction on the U8 RNA is presented. RNAs with mutations, insertions, or
deletions within the 5'-most 15 nucleotides of U8 do not function in
pre-rRNA processing. In vivo competitions in Xenopus oocytes with
2'O-methyl oligoribonucleotides have confirmed this region as a functional
site of a base-pairing interaction. Cross-species hybrid molecules of U8
RNA show that this region of the U8 snoRNP is necessary for processing of
pre-rRNA but not sufficient to direct efficient cleavage of the pre-rRNA
substrate; the structure or proteins comprising, or recruited by, the U8
snoRNP modulate the efficiency of cleavage. Intriguingly, these 15
nucleotides have the potential to base pair with the 5' end of 28S rRNA in
a region where, in the mature ribosome, the 5' end of 28S interacts with
the 3' end of 5.8S. The 28S- 5.8S interaction is evolutionarily conserved
and critical for pre-rRNA processing in Xenopus laevis. Taken together
these data strongly suggest that the 5' end of U8 RNA has the potential to
bind pre-rRNA and in so doing, may regulate or alter the pre-rRNA folding
pathway. The rest of the U8 particle may then facilitate cleavage or
recruitment of other factors which are essential for pre-rRNA processing.
Copyright © 1997, American Society for Microbiology
The sequence of the 5' end of the U8 small nucleolar RNA is critical for 5.8S and 28S rRNA maturation
Genetics and Biochemistry Branch, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, Maryland 20892-1766, USA. bp51h@nih.gov
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