Mechanisms of human mRNA packaging and export

ongoing

Eukaryotic gene expression is partitioned across two cellular compartments: the nucleus, where messenger RNA (mRNA) is produced, and the cytoplasm, where protein translation occurs. mRNA export across the nuclear membrane is highly selective, ensuring that only fully processed and mature mRNA is transported to the cytoplasm. Yet how does the multi-step mRNA maturation process converge to a binary decision, ‘to export or not to export’? While we know many of the proteins involved in packaging and export of nuclear mRNA ribonucleoprotein complexes (mRNPs), how a defined set of conserved proteins package and export all nuclear mRNA remains poorly understood. To reveal how specificity towards mature mRNA is achieved and to identify regulatory checkpoints, I propose to visualize key mRNP intermediates using a state-of-the-art integrative structural biology approach. First, we will determine the human THO/TREX complex structure to reveal how this key packaging factor is organized and brought to mRNA (aim 1). Second, we will determine the structure of a human mRNP 5’-end to explain how two key features of mature mRNPs, the 5’-cap and the first splice junction, are recognized and integrated by THO/TREX to achieve export competence (aim 2). Third, we will obtain the architecture of endogenous human mRNPs to reveal their dynamics and to determine how mRNAs of varied length and sequence are packaged (aim 3). These data will enable the complementary and targeted in vitro and in vivo structure-function analysis. Taken together, the expected results will reveal novel insights into the mechanisms that underlie an important step of gene expression, which mediates nuclear mRNA quality control and links transcription to translation. My background in structural biology, mRNA transcription and processing is ideally suited to carry out this high-impact proposal.