Ngl2p is a Ccr4p-like RNA nuclease essential for the final step in 3???-end processing of 5.8S rRNA in Saccharomyces cerevisiae

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Abstract
Saccharomyces cerevisiae contains three nonessential genes (NGL1, NGL2, and NGL3) that encode proteins containing a domain with similarity to a Mg2+-dependent endonuclease motif present in the mRNA deadenylase Ccr4p. We have investigated a possible role of these proteins in rRNA processing, because for many of the pre-rRNA processing steps, the identity of the responsible nuclease remains elusive. Analysis of RNA isolated from cells in which the NGL2 gene has been inactivated (ngl2Δ) demonstrates that correct 3′-end formation of 5.8S rRNA at site E is strictly dependent on Ngl2p. No role in pre-rRNA processing could be assigned to Ngl1p and Ngl3p. The 3′-extended 5.8S rRNA formed in the ngl2Δ mutant is slightly shorter than the 6S precursor previously shown to accumulate upon combined deletion of the 3′ → 5′ exonuclease-encoding REX1 and REX2 genes or upon depletion of the exosomal subunits Rrp40p or Rrp45p. Thus, our data add a further component to the set of nucleases required for correct 3′-end formation of yeast 5.8S rRNA.