The small nucleolar RNP protein NOP1 (fibrillarin) is required for pre-rRNA processing in yeast

D. Tollervey, H. Lehtonen, M. Carmo-Fonseca, E. C. Hurt

Research output: Contribution to journalArticlepeer-review


The yeast snoRNP protein, NOP1, is structurally and functionally homologous to vertebrate fibrillarin and is essential for viability. A conditionally lethal allele was constructed by placing NOP1 expression under the controlof a GAL promoter. Growth on glucose medium results in the depletion of NOP1 over several generations, during which cell growth is progressively impaired. Pulse labelling of proteins shows that NOP1 depleted strains are greatly impaired in the production of cytoplasmic ribosomes, and they have a reduced level of rRNA. Northern hyhridization and pulse-chase labelling of pre-rRNA show a progressive impairment of all pre-rRNA processing steps. The pathway leading to 18S rRNA is particularly affected. Methylation of pre-rRNA is concomitantly impaired and unmethylated pre-rRNA accumulates and is not processed over long periods. NOP1 depletion does not prevent the accumulation of seven snoRNAs tested including U3; the levels of two species, U14 and snR190, decline. The snoRNAs synthesized in the ahsence of NOP1 retain TMG cap structures. Subnuclear fractionation and immunocytochemistry indicate that they continue to be localized in the nucleolus.

Original languageEnglish
Pages (from-to)573-583
Number of pages11
JournalEMBO Journal
Issue number3
Publication statusPublished - 18 Mar 1991


  • nucleolus
  • pre-rRNA processing
  • Saccharomyces cerevisiae
  • snRNA
  • snRNP


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