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Mol. Cell. Biol., Dec 1997, 7088-7098, Vol 17, No. 12
T Gautier, T Berges, D Tollervey and E Hurt
Different point mutations in the nucleolar protein fibrillarin (Nop1p in
Saccharomyces cerevisiae) can inhibit different steps in ribosome
synthesis. A screen for mutations that are synthetically lethal (sl) with
the nop1-5 allele, which inhibits pre-rRNA processing, identified NOP56. An
independent sl mutation screen with nop1-3, which inhibits pre-rRNA
methylation, identified a mutation in NOP58. Strikingly, Nop56p and Nop58p
are highly homologous (45% identity). Both proteins were found to be
essential and localized to the nucleolus. A temperature-sensitive lethal
mutant allele, nop56-2, inhibited many steps in pre-rRNA processing,
particularly on the pathway of 25S/5.8S rRNA synthesis, and led to defects
in 60S subunit assembly. Epitope- tagged constructs show that both Nop56p
and Nop58p are associated with Noplp in complexes, Nop56p and Nop1p
exhibiting a stoichiometric association. These physical interactions
presumably underlie the observed sl phenotypes. Well-conserved homologs are
present in a range of organisms, including humans (52% identity between
human hNop56p and yeast Nop56p), suggesting that these complexes have been
conserved in evolution.
Copyright © 1997, American Society for Microbiology
Nucleolar KKE/D repeat proteins Nop56p and Nop58p interact with Nop1p and are required for ribosome biogenesis
Laboratoire DyOGen, Institut Albert Bonniot, Universite Grenoble I, La Tronche, France.
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