Biochemical dissection, functional characterization and regulatory cues of the assembly machinery for U snRNPs

• Applicants: Professor Dr. Utz Fischer; Professor Dr. Oliver Gruß
• Subject Area: Cell Biology
• Term: from 2009 to 2022
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 119111219

Macromolecular complexes composed of proteins or proteins and nucleic acids perform a wide spectrum of different cellular tasks. The assembly of these macromolecular complexes often depends on trans-acting factors in vivo, as isolated subunits may aggregate or engage in wrong interactions. A paradigm for assisted assembly is the formation of the common Sm/LSm core of spliceosomal and histone-mRNA processing U snRNPs. The key assembly factors of this process are united in PRMT5- and SMN-complexes and facilitate binding of seven Sm/LSm proteins onto U snRNA. Assembly is initiated by the PRMT5-complex subunit pICln, which pre-arranges Sm/LSm proteins into spatial positions occupied in the mature U snRNP. The SMN complex then takes over these Sm/LSm units, displaces pICln and unites them with U snRNA. We have shown in the past funding period that newly synthesized Sm/LSm proteins remain bound to the ribosome even upon translation termination and that Sm/LSm guidance into the assembly pathway is dependent on pICln. Our studies uncovered an elaborate assembly line for U snRNPs in which the ribosome plays a crucial part as a quality control hub and the starting point for the chaperone-mediated assembly process. Building on these findings we are now planning to test the hypothesis that the coordinated hand-over of Sm/LSm proteins from the ribosome to the assembly machinery prevents their mis-assembly and/or aggregation and determines cellular U snRNP biogenesis. The second part of the proposal builds on our finding that several components of the SMN complex are phosphorylated and that this post-translational modification impacts on the function and sub-cellular distribution of the SMN complex. We aim to identify and further characterize signalling cues that modify the SMN complex and propose experiments that will shed light on the functional relevance of these modifications for U snRNP biogenesis and homeostasis.

• DFG Programme: Research Grants