The final step in the formation of 25S rRNA in saccharomyces cerevisiae is performed by 5'->3' exonucleases

T.H. Geerlings, J.C. Vos, H.A. Raue

Research output: Contribution to JournalArticleAcademicpeer-review

Abstract

The final stage in the formation of the two large subunit rRNA species in Saccharomyces cerevisiae is the removal of internal transcribed spacer 2 (ITS2) from the 27SB precursors. This removal is initiated by endonucleolytic cleavage approximately midway in ITS2. The resulting 7S pre-rRNA, which is easily detectable, is then converted into 5.8S rRNA by the concerted action of a number of 3' → 5' exonucleases, many of which are part of the exosome. So far the complementary precursor to 25S rRNA resulting from the initial cleavage in ITS2 has not been detected and the manner of its conversion into the mature species is unknown. Using various yeast strains that carry different combinations of wild-type and mutant alleles of the major 5' → 3' exonucleases Ratlp and Xrnlp, we now demonstrate the existence of a short-lived 25.5S pre-rRNA whose 5' end is located closely downstream of the previously mapped 3' end of 7S pre-rRNA. The 25.5S pre-rRNA is converted into mature 25S rRNA by rapid exonucleolytic trimming, predominantly carried out by Ratlp. In the absence of Rat1p, however, the removal of the ITS2 sequences from 25.5S pre-rRNA can also be performed by Xrnlp, albeit somewhat less efficiently.
Original languageEnglish
Pages (from-to)1698-1703
Number of pages5
JournalRNA
Volume6
DOIs
Publication statusPublished - 2000

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