Messenger RNA (mRNA) is the genetic carrier of information from DNA to protein. In eukaryotes, mRNA production in the nucleus is separated from mRNA translation in the cytoplasm. This separation requires mechanisms for selective mRNA transport, to ensure that only fully matured mRNAs are transported into the cytoplasm and yield functional proteins. Despite its importance, the molecular basis for how mature mRNAs are recognised, discriminated from immature precursors, and prepared ('packaged') for nuclear export remains poorly understood. Further, defects in mRNA maturation and packaging are frequently linked with disease, such as cancer. A molecular understanding of these key gene expression steps may therefore aid in the therapeutic treatment of disease. In this project, we combine structural and functional studies to study how the essential and conserved transcription-export export complex selects and packages human mRNA-protein complexes for productive nuclear export. Further, we aim to understand how human mRNPs organize in three-dimensions, which is important to understand mRNA regulation. Towards these goals, we defined three objectives to (1) determine the three-dimensional structure of the transcription-export complex, (2) of parts of mRNA-protein complexes, and (3) of complete maturing human mRNPs. Combined with functional validation of the structural data, we expect that these findings will make a major contribution to our understanding of human mRNA packaging and export. In the current reporting period, we have completed aim 1, and are making progress towards aims 2 and 3. Our current results are summarised in two publications (Puehringer et al., eLife, 2020; Pacheco-Fiallos et al., Nature, 2023), which provide novel mechanisms for how human mRNPs are recognised and packaged for mRNA nuclear export.
