Structure of the RBM7-ZCCHC8 core of the NEXT complex reveals connections to splicing factors.

Sebastian Falk,Mireille Melko,Christian Benda,Søren Lykke-Andersen,Torben Heick Jensen,Ksenia Finogenova,Elena Conti

doi:10.1038/ncomms13573

Sebastian Falk, Mireille Melko + Show 5 more

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https://doi.org/10.1038/ncomms13573

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Abstract

The eukaryotic RNA exosome participates extensively in RNA processing and degradation. In human cells, three accessory factors (RBM7, ZCCHC8 and hMTR4) interact to form the nuclear exosome targeting (NEXT) complex, which directs a subset of non-coding RNAs for exosomal degradation. Here we elucidate how RBM7 is incorporated in the NEXT complex. We identify a proline-rich segment of ZCCHC8 as the interaction site for the RNA-recognition motif (RRM) of RBM7 and present the crystal structure of the corresponding complex at 2.0 Å resolution. On the basis of the structure, we identify a proline-rich segment within the splicing factor SAP145 with strong similarity to ZCCHC8. We show that this segment of SAP145 not only binds the RRM region of another splicing factor SAP49 but also the RRM of RBM7. These dual interactions of RBM7 with the exosome and the spliceosome suggest a model whereby NEXT might recruit the exosome to degrade intronic RNAs.

Highlights

The eukaryotic RNA exosome participates extensively in RNA processing and degradation
Since full-length RBM7 precipitated during purification, we used a truncated fragment of RBM7 lacking part of the unstructured C-terminal region of the protein
We found that RBM71–137 co-precipitated with GST-ZCCHC8, but not with GST-hMTR4 (Fig. 1b, lanes 7 and 8)

Summary

Introduction

The eukaryotic RNA exosome participates extensively in RNA processing and degradation. Three accessory factors (RBM7, ZCCHC8 and hMTR4) interact to form the nuclear exosome targeting () complex, which directs a subset of non-coding RNAs for exosomal degradation. RBM7/ interacts with the exosome and with proteins (ZC3H18 and ARS2) that connect it to the nuclear cap-binding complex, which resides on the 50-cap structures of nuclear RNA polymerase II-derived transcripts[30,32] While this presumably explains the moderate cap-proximal nature of RBM7 binding to RNA in cells, it has remained unclear how RBM7/ gets targeted to the 30-ends of introns[31].

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