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  • Title: Rat1p and Rai1p function with the nuclear exosome in the processing and degradation of rRNA precursors.
    Author: Fang F, Phillips S, Butler JS.
    Journal: RNA; 2005 Oct; 11(10):1571-8. PubMed ID: 16131592.
    Abstract:
    Exoribonucleases function in the processing and degradation of a variety of RNAs in all organisms. These enzymes play a particularly important role in the maturation of rRNAs and in a quality-control pathway that degrades rRNA precursors upon inhibition of ribosome biogenesis. Strains with defects in 3'-5' exoribonucleolytic components of the RNA processing exosome accumulate polyadenylated precursor rRNAs that also arise in strains with ribosome biogenesis defects. These findings suggested that polyadenylation might target pre-rRNAs for degradation by the exosome. Here we report experiments that indicate a role for the 5'-3' exoribonuclease Rat1p and its associated protein Rai1p in the degradation of poly(A)(+) pre-rRNAs. Depletion of Rat1p enhances the amount of poly(A)(+) pre-rRNA that accumulates in strains deleted for the exosome subunit Rrp6p and decreases their 5' heterogeneity. Deletion of RAI1 results in the accumulation of poly(A)(+) pre-rRNAs, and inhibits Rat1p-dependent 5'-end processing and Rrp6p-dependent 3'-end processing of 5.8S rRNA. RAT1 and RAI1 mutations cause synergistic growth defects in the presence of rrp6-Delta, consistent with the interdependence of 5'-end and 3'-end processing pathways. These findings suggest that Rai1p may coordinate the 5'-end and 3'-end processing and degradation activities of Rat1p and the nuclear exosome.
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