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Related Experiment Video

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Functional Characterization of RING-Type E3 Ubiquitin Ligases In Vitro and In Planta
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Structure and function of the 5'-->3' exoribonuclease Rat1 and its activating partner Rai1.

Song Xiang1, Amalene Cooper-Morgan, Xinfu Jiao

  • 1Department of Biological Sciences, Columbia University, New York, New York 10027, USA.

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|February 6, 2009
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Summary

The study reveals how Rai1 activates the Rat1 exoribonuclease, enhancing its ability to degrade RNA. This research uncovers a novel pyrophosphohydrolase activity in Rai1, suggesting new roles in eukaryotic RNA metabolism.

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Area of Science:

  • Biochemistry
  • Molecular Biology
  • Structural Biology

Background:

  • 5'-->3' exoribonucleases (XRNs) are crucial for RNA metabolism and interference in eukaryotes.
  • XRN2 (Rat1 in yeast) functions in the nucleus and is vital for transcription termination by RNA polymerase II.
  • The exoribonuclease activity of Rat1 is known to be stimulated by the protein Rai1.

Purpose of the Study:

  • To elucidate the molecular mechanism of Rat1 activation by Rai1.
  • To determine the structural basis for Rat1's exoribonuclease activity.
  • To investigate potential novel functions of Rai1/Dom3Z in RNA metabolism.

Main Methods:

  • X-ray crystallography was used to determine the structures of Schizosaccharomyces pombe Rat1 in complex with Rai1, and of Rai1 and murine Dom3Z alone.
  • Biochemical assays were performed to confirm structural observations and assess exoribonuclease activity.
  • Site-directed mutagenesis was employed to investigate the function of conserved residues in Rai1.

Main Results:

  • The crystal structures revealed the mechanism by which Rai1 activates Rat1 and confers exclusive exoribonuclease activity.
  • Rai1 was shown to enhance Rat1's degradation of RNAs with stable secondary structures.
  • A novel pyrophosphohydrolase activity of Rai1 towards 5' triphosphorylated RNA was discovered, with conserved residues in a unique pocket coordinating a divalent cation.

Conclusions:

  • Rai1 acts as a crucial activator of the Rat1 exoribonuclease, with structural insights into the mechanism.
  • The findings suggest that Rai1/Dom3Z may possess additional, previously unrecognized functions in eukaryotic RNA metabolism, particularly in processing 5' triphosphorylated RNA.
  • This study expands our understanding of RNA degradation pathways and the roles of XRN family enzymes in eukaryotes.