Yeast exosome mutants accumulate 3'-extended polyadenylated forms of U4 small nuclear RNA and small nucleolar RNAs.
The exosome is a protein complex consisting of a variety of 3'-to-5' exonucleases that functions both in 3'-to-5' trimming of rRNA precursors and in 3'-to-5' degradation of mRNA. To determine additional exosome functions, we examined the processing of a variety of RNAs, including tRNAs, small nuclear RNAs (snRNAs), small nucleolar RNAs (snoRNAs), RNase P, RNase MRP, and SRP RNAs, and 5S rRNAs in mutants defective in either the core components of the exosome or in other proteins required for exosome function. These experiments led to three important conclusions. First, exosome mutants accumulate 3'-extended forms of the U4 snRNA and a wide variety of snoRNAs, including snoRNAs that are independently transcribed or intron derived. This finding suggests that the exosome functions in the 3' end processing of these species. Second, in exosome mutants, transcripts for U4 snRNA and independently transcribed snoRNAs accumulate as 3'-extended polyadenylated species, suggesting that the exosome is required to process these 3'-extended transcripts. Third, processing of 5.8S rRNA, snRNA, and snoRNA by the exosome is affected by mutations of the nuclear proteins Rrp6p and Mtr4p, whereas mRNA degradation by the exosome required Ski2p and was not affected by mutations in RRP6 or MTR4. This finding suggests that the cytoplasmic and nuclear forms of the exosome represent two functionally different complexes involved in distinct 3'-to-5' processing and degradation reactions.
van Hoof
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Department of Molecular Biology, Howard Hughes Medical Institute, University of Arizona, Tucson, Arizona 85721, USA.
Lennertz
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Parker
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D053487:DEAD-box RNA Helicases; D004722:Endoribonucleases / Q000378:metabolism; D005095:Exoribonucleases / Q000235:genetics / Q000378:metabolism*; D063326:Exosome Multienzyme Ribonuclease Complex; D005656:Fungal Proteins / Q000235:genetics / Q000378:metabolism; D005796:Genes / Q000235:genetics; D005800:Genes, Fungal / Q000235:genetics / Q000502:physiology; D007438:Introns / Q000235:genetics; D007700:Kinetics; D009097:Multienzyme Complexes / Q000235:genetics / Q000378:metabolism; D009154:Mutation / Q000235:genetics*; D010641:Phenotype; D011061:Poly A / Q000235:genetics / Q000378:metabolism*; D020365:RNA Helicases / Q000235:genetics / Q000378:metabolism; D012323:RNA Processing, Post-Transcriptional / Q000235:genetics*; D012331:RNA, Fungal / Q000235:genetics / Q000378:metabolism; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D012342:RNA, Small Nuclear / Q000235:genetics / Q000378:metabolism*; D020537:RNA, Small Nucleolar / Q000235:genetics / Q000378:metabolism*; D016601:RNA-Binding Proteins / Q000235:genetics / Q000378:metabolism; D043244:Ribonuclease III; D012441:Saccharomyces cerevisiae / Q000201:enzymology / Q000235:genetics*; D029701:Saccharomyces cerevisiae Proteins; D014158:Transcription, Genetic / Q000235:genetics
D005656:Fungal Proteins; D009097:Multienzyme Complexes; D012331:RNA, Fungal; D012333:RNA, Messenger; D012342:RNA, Small Nuclear; D020537:RNA, Small Nucleolar; D016601:RNA-Binding Proteins; D029701:Saccharomyces cerevisiae Proteins; D011061:Poly A; D004722:Endoribonucleases; D005095:Exoribonucleases; D063326:Exosome Multienzyme Ribonuclease Complex; C112610:RRP6 protein, S cerevisiae; C468367:RNT1 protein, S cerevisiae; D043244:Ribonuclease III; C101004:MTR4 protein, S cerevisiae; D053487:DEAD-box RNA Helicases; D020365:RNA Helicases