Mixed Messages: Dynamic and Compositional Heterogeneity of Nuclear Messenger Ribonucleoprotein (mRNP) Complexes

Messenger ribonucleoprotein (mRNP) complexes assemble co-transcriptionally in the nucleus as RNA-binding proteins (RBPs) engage nascent transcripts. Ongoing RNA processing and RBP dynamics generate a diverse set of mRNPs, often producing a mature mRNA-capped, spliced, and polyadenylated-within a compact mRNP particle poised for nuclear export. The processing, packaging, and export of nuclear mRNPs are tightly regulated to ensure the fidelity of gene expression and to reprogram cellular function under changing organismal and environmental conditions. Understanding the compositional and organizational dynamics of nuclear mRNP assembly and maturation is essential, as dysregulation is linked to viral infections and a range of human diseases, including neurological disorders and cancer. Recent structural, biochemical, and in-cell studies have revealed key roles for the evolutionarily conserved Yra1/ALYREF proteins and the TRanscription-EXport (TREX) complex in mRNP packaging and export, highlighting broadly conserved functions across eukaryotes. While many questions remain, these advances have deepened our understanding of nuclear mRNA metabolism and offer new opportunities to investigate how disruptions in mRNA biogenesis and export factors, and their associated processes, contribute to disease. This article is categorized under: RNA Interactions with Proteins and Other Molecules > RNA-Protein Complexes RNA Interactions with Proteins and Other Molecules > Protein-RNA Interactions: Functional Implications RNA Export and Localization > Nuclear Export/Import.