Processing of the intron-encoded U18 small nucleolar RNA in the yeast Saccharomyces cerevisiae relies on both exo- and endonucleolytic activities.
Many small nucleolar RNAs (snoRNAs) are encoded within introns of protein-encoding genes and are released by processing of their host pre-mRNA. We have investigated the mechanism of processing of the yeast U18 snoRNA, which is found in the intron of the gene coding for translational elongation factor EF-1beta. We have focused our analysis on the relationship between splicing of the EF-1beta pre-mRNA and production of the mature snoRNA. Mutations inhibiting splicing of the EF-1beta pre-mRNA have been shown to produce normal U18 snoRNA levels together with the accumulation of intermediates deriving from the pre-mRNA, thus indicating that the precursor is an efficient processing substrate. Inhibition of 5'-->3' exonucleases obtained by insertion of G cassettes or by the use of a rat1-1 xrn1Delta mutant strain does not impair U18 release. In the Exo- strain, 3' cutoff products, diagnostic of an endonuclease-mediated processing pathway, were detected. Our data indicate that biosynthesis of the yeast U18 snoRNA relies on two different pathways, depending on both exonucleolytic and endonucleolytic activities: a major processing pathway based on conversion of the debranched intron and a minor one acting by endonucleolytic cleavage of the pre-mRNA.
Villa
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Istituto Pasteur-Fondazione Cenci Bolognetti, Dipartimento di Genetica e Biologia Molecolare, Università "La Sapienza," Rome, Italy.
Ceradini
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F
Presutti
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Bozzoni
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I
D004268:DNA-Binding Proteins / Q000378:metabolism; D004706:Endodeoxyribonucleases / Q000378:metabolism*; D043211:Exodeoxyribonuclease V; D005090:Exodeoxyribonucleases / Q000378:metabolism*; D005095:Exoribonucleases / Q000378:metabolism*; D005656:Fungal Proteins / Q000235:genetics / Q000378:metabolism; D007438:Introns; D020648:Peptide Elongation Factor 1; D010445:Peptide Elongation Factors / Q000235:genetics / Q000378:metabolism; D012322:RNA Precursors / Q000378:metabolism; D012326:RNA Splicing; D012342:RNA, Small Nuclear / Q000235:genetics*; D012261:Ribonucleoproteins / Q000235:genetics / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000235:genetics*; D029701:Saccharomyces cerevisiae Proteins
D004268:DNA-Binding Proteins; D005656:Fungal Proteins; D020648:Peptide Elongation Factor 1; D010445:Peptide Elongation Factors; D012322:RNA Precursors; D012342:RNA, Small Nuclear; D012261:Ribonucleoproteins; D029701:Saccharomyces cerevisiae Proteins; C075577:RAT1 protein, S cerevisiae; D004706:Endodeoxyribonucleases; D005090:Exodeoxyribonucleases; D005095:Exoribonucleases; C068398:XRN1 protein, S cerevisiae; D043211:Exodeoxyribonuclease V