ICln-Sm interactions

Sm proteins bind to "uridine rich small nuclear ribonucleic acid" (UsnRNA) and are thus an integral part of the spliceosome, a macromolecular machine that catalyzes the removal of introns from pre-mRNA. The methylosome is a protein complex that contains the type II methyltransferase JBP1 and symmetrically dimethylates the Sm proteins D1, D3 and possibly B/B`. Once methylated, these Sm proteins bind to the "Survival of Motor Neuron" (SMN) complex, which will facilitate their transfer to UsnRNA. Sm proteins and the methylosome interact with ICln, a protien that assists cell volume regulation. In splicing, ICln is believed to sequester Sm proteins in the cytosol and thus to direct these proteins into a pathway that allows a coordinated assembly of the spliceosome. The interactions between Sm proteins, the methylosome and ICln per se have been described in vitro, but no information on the dynamics of these interactions in the living cell as well as the structure and hence functioning of these complexes is available. It is the aim of this study to combine structural proteomics and cell biology to investigate the structure of ICln-Sm complexes by NMR and electron microscopy, and to study the spatiotemporal regulation of ICln-Sm interactions in the living cell under physiologically relevant conditions. Results of this study can contribute to a better understanding of the structural basis and hence the functioning of ICln-Sm complexes, their assembly, the methylation of Sm proteins by the methylosome, and the involvement of ICln in this process.

Sm proteins bind to "uridine rich small nuclear ribonucleic acid" (UsnRNA) and are thus an integral part of the spliceosome, a macromolecular machine that catalyzes the removal of introns from pre-mRNA. The methylosome is a protein complex that contains the type II methyltransferase JBP1 and symmetrically dimethylates the Sm proteins D1, D3 and possibly B/B`. Once methylated, these Sm proteins bind to the "Survival of Motor Neuron" (SMN) complex, which will facilitate their transfer to UsnRNA. Sm proteins and the methylosome interact with ICln, a protien that assists cell volume regulation. In splicing, ICln is believed to sequester Sm proteins in the cytosol and thus to direct these proteins into a pathway that allows a coordinated assembly of the spliceosome. The interactions between Sm proteins, the methylosome and ICln per se have been described in vitro, but no information on the dynamics of these interactions in the living cell as well as the structure and hence functioning of these complexes is available. It is the aim of this study to combine structural proteomics and cell biology to investigate the structure of ICln-Sm complexes by NMR and electron microscopy, and to study the spatiotemporal regulation of ICln-Sm interactions in the living cell under physiologically relevant conditions. Results of this study can contribute to a better understanding of the structural basis and hence the functioning of ICln-Sm complexes, their assembly, the methylation of Sm proteins by the methylosome, and the involvement of ICln in this process.