TREXSpliceosome · Investigating the structural basis of TREX function in mRNA export using cryo-electron microscopy and super-resolution fluorescence microscopy

Eukaryotic mRNA is transcribed, capped, spliced and poly-adenylated in the nucleus, but translated in the cytoplasm. Nuclear mRNA export is a key step in gene expression which is still poorly understood in mechanistic detail, but the multi-subunit transcription and export (TREX) complex plays a central role in the process. TREX bridges transcription, RNA processing and packaging to facilitate mRNA export licensing. Understanding TREX function is relevant to human health, as TREX protects against transcription-associated genome instability, is required for development, and has been linked to human disease, including several types of cancer. Despite its importance, many questions about TREX function remain, in particular, how is TREX recruited to mRNA and how is the export factor NXF1-NXT1 deposited on mature mRNA? Here, I propose to study the mechanistic basis of TREX recruitment and function using structural biology and imaging approaches. The host laboratory recently purified an endogenous multi-megadalton spliceosome–TREX complex, whose three-dimensional cryo-EM structure I aim to determine. This will reveal how TREX is recruited to maturing mRNA to read out and relay the presence of activating and repressive marks to, ultimately, decide whether or not to export the mRNA. In close collaboration with the Balzarotti lab (IMP), I will use super-resolution microscopy (MINFLUX) to visualize post-recruitment functions of TREX in situ and test models of how deposition of the mRNA export factor NXF1-NXT is linked to export competence. Taken together, the proposed work will significantly enhance our understanding of TREX as a chaperone of nuclear mRNA processing and export.