The C-terminal domain of coilin interacts with Sm proteins and U snRNPs |
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Authors: | Hongzhi Xu Ramesh S. Pillai Teldja N. Azzouz Karl B. Shpargel Christian Kambach Michael D. Hebert Daniel Schümperli A. Gregory Matera |
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Affiliation: | (1) Department of Biochemistry, The University of Mississippi Medical Center, Jackson, MS 39216-4505, USA;(2) Institute of Cell Biology, University of Bern, Baltzerstrasse 4, 3012 Bern, Switzerland;(3) Department of Genetics, Case Western Reserve University, 10900 Euclid Avenue, Cleveland, OH 44106-4955, USA;(4) Paul Scherrer Institute, Life Sciences, 5232 Villigen PSI, Switzerland;(5) Present address: Friedrich Miescher Institute, Maulbeerstrasse 66, 4058 Basel, Switzerland |
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Abstract: | Coilin is the signature protein of the Cajal body (CB), a nuclear suborganelle involved in the biogenesis of small nuclear ribonucleoproteins (snRNPs). Newly imported Sm-class snRNPs are thought to traffic through CBs before proceeding to their final nuclear destinations. Loss of coilin function in mice leads to significant viability and fertility problems. Coilin interacts directly with the spinal muscular atrophy (SMA) protein via dimethylarginine residues in its C-terminal domain. Although coilin hypomethylation results in delocalization of survival of motor neurons (SMN) from CBs, high concentrations of snRNPs remain within these structures. Thus, CBs appear to be involved in snRNP maturation, but factors that tether snRNPs to CBs have not been described. In this report, we demonstrate that the coilin C-terminal domain binds directly to various Sm and Lsm proteins via their Sm motifs. We show that the region of coilin responsible for this binding activity is separable from that which binds to SMN. Interestingly, U2, U4, U5, and U6 snRNPs interact with the coilin C-terminal domain in a glutathione S-transferase (GST)-pulldown assay, whereas U1 and U7 snRNPs do not. Thus, the ability to interact with free Sm (and Lsm) proteins as well as with intact snRNPs, indicates that coilin and CBs may facilitate the modification of newly formed snRNPs, the regeneration of ‘mature’ snRNPs, or the reclamation of unassembled snRNP components. |
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