Rat1p and Rai1p function with the nuclear exosome in the processing and degradation of rRNA precursors.
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.
Fang
Feng
F
Department of Microbiology and Immunology, University of Rochester Medical Center, Rochester, NY 14642, USA.
Phillips
Seasson
S
Butler
J Scott
JS
D000963:Antimetabolites / Q000494:pharmacology; D005095:Exoribonucleases / Q000235:genetics / Q000378:metabolism*; D005472:Fluorouracil / Q000494:pharmacology; D005656:Fungal Proteins / Q000378:metabolism*; D008954:Models, Biological; D009687:Nuclear Proteins / Q000235:genetics / Q000378:metabolism*; D012322:RNA Precursors / Q000378:metabolism*; D012323:RNA Processing, Post-Transcriptional; D012331:RNA, Fungal / Q000235:genetics / Q000378:metabolism; D012335:RNA, Ribosomal / Q000378:metabolism; D016601:RNA-Binding Proteins; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012441:Saccharomyces cerevisiae / Q000201:enzymology / Q000235:genetics / Q000254:growth & development / Q000378:metabolism; D029701:Saccharomyces cerevisiae Proteins / Q000235:genetics / Q000378:metabolism*
D000963:Antimetabolites; D005656:Fungal Proteins; D009687:Nuclear Proteins; D012322:RNA Precursors; D012331:RNA, Fungal; D012335:RNA, Ribosomal; D016601:RNA-Binding Proteins; C473024:Rai1 protein, S cerevisiae; D029701:Saccharomyces cerevisiae Proteins; C075577:RAT1 protein, S cerevisiae; D005095:Exoribonucleases; D005472:Fluorouracil