Schillewaert S, Wacheul L, Lhomme F, Lafontaine DL

Ribosome synthesis entails the formation of mature rRNAs from long precursor molecules, following a complex pre-rRNA processing pathway. Why the generation of mature rRNA ends is so complicated is unclear? Nor is it understood how pre-rRNA processing is coordinated at distant sites on pre-rRNA molecules. Here we characterized, in budding ...

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yeast and human cells, the evolutionarily conserved protein Las1. We found that in both species, Las1 is required to process ITS2, which separates the 5.8S and 25S/28S rRNAs. In yeast, Las1 is required for pre-rRNA processing at both ends of ITS2. It is required for Rrp6-dependent formation of the 5.8S rRNA 3' -end and for Rat1-dependent formation of the 25S rRNA 5' -end. We further show that the Rat1-Rai 5' -3' exoRNase complex functionally connects processing at both ends of the 5.8S rRNA. We suggest that pre-rRNA processing is coordinated at both ends of 5.8S rRNA and both ends of ITS2, which are brought together by pre-rRNA folding, by an RNA processing complex. Consistently, we note the conspicuous presence of ∼7/8 nucleotides extensions on both ends of 5.8S rRNA precursors and at the 5' -end of pre-25S RNAs suggestive of a protected spacer fragment of similar length.

Date: Nov. 14, 2011

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