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Mol Cell. 2008 Mar 28;29(6):717-28. doi: 10.1016/j.molcel.2008.02.018.

Structure of the active subunit of the yeast exosome core, Rrp44: diverse modes of substrate recruitment in the RNase II nuclease family.

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European Molecular Biology Laboratory, Meyerhofstrasse 1, D-69117 Heidelberg, Germany.


The eukaryotic exosome is a macromolecular complex essential for RNA processing and decay. It has recently been shown that the RNase activity of the yeast exosome core can be mapped to a single subunit, Rrp44, which processively degrades single-stranded RNAs as well as RNAs containing secondary structures. Here we present the 2.3 A resolution crystal structure of S. cerevisiae Rrp44 in complex with single-stranded RNA. Although Rrp44 has a linear domain organization similar to bacterial RNase II, in three dimensions the domains have a different arrangement. The three domains of the classical nucleic-acid-binding OB fold are positioned on the catalytic domain such that the RNA-binding path observed in RNase II is occluded. Instead, RNA is threaded to the catalytic site via an alternative route suggesting a mechanism for RNA-duplex unwinding. The structure provides a molecular rationale for the observed biochemical properties of the RNase R family of nucleases.

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