Project description:The nuclear export of messenger RNAs (mRNAs) is intimately coupled to their synthesis. pre-mRNAs assemble into dynamic ribonucleoparticles as they are being transcribed, processed and exported. The role of ubiquitylation in this process is increasingly recognized as the ubiquitylation of many key players have been shown to affect mRNA nuclear export. While a few E3 ligases have been shown to regulate nuclear export, evidence for deubiquitylases is currently lacking. Here, we identified the deubiquitylase Ubp15 as a regulator of nuclear export in Saccharomyces cerevisiae. Ubp15 interacts both with RNA polymerase II and with the nuclear pore complex, and its deletion reverts the nuclear export defect of mutants of the E3 ligase Rsp5. The deletion of UBP15 leads to hyper-ubiquitylation of the main nuclear export receptor Mex67 and affects its association with THO, a complex coupling transcription to mRNA processing and involved in the recruitment of mRNA export factors to nascent transcripts. Collectively, our data support a role for Ubp15 in coupling transcription to mRNA export.
Project description:Transcription termination and mRNA export from the nucleus are closely regulated and coordinated processes. Nuclear export factors are recruited to actively transcribed genes through their interactions with protein complexes associated with transcription and co-transcriptional pre-mRNA processing. We determine a new role for the kinase WNK1 in the cross-talk of transcription termination and mRNA export. WNK1 was previously attributed a cytoplasmic role as a regulator of ion transport. However, we now show a nuclear function for this kinase where it is required for efficient mRNA export along with the transcription termination factor PCF11. Finally, we identify the phosphorylation of the CID domain of PCF11 as an important step for the release of the mRNA from the transcription locus, thus allowing efficient mRNA export to the cytoplasm.
Project description:Nuclear export of messenger RNAs (mRNAs) is intimately coupled to their synthesis. pre-mRNAs assemble into dynamic ribonucleoparticles as they are being transcribed, processed, and exported. The role of ubiquitylation in this process is increasingly recognized but, while a few E3 ligases have been shown to regulate nuclear export, evidence for deubiquitylases is currently lacking. Here we identified deubiquitylase Ubp15 as a regulator of nuclear export in Saccharomyces cerevisiae. Ubp15 interacts with both RNA polymerase II and the nuclear pore complex, and its deletion reverts the nuclear export defect of E3 ligase Rsp5 mutants. The deletion of UBP15 leads to hyper-ubiquitylation of the main nuclear export receptor Mex67 and affects its association with THO, a complex coupling transcription to mRNA processing and involved in the recruitment of mRNA export factors to nascent transcripts. Collectively, our data support a role for Ubp15 in coupling transcription to mRNA export.
Project description:The eukaryotic mRNA life cycle includes transcription, nuclear mRNA export and degradation. To quantify all these processes simultaneously, we perform thiol-linked alkylation after metabolic labeling of RNA with 4-thiouridine (4sU), followed by sequencing of RNA (SLAM-seq) in the nuclear and cytosolic compartments. We develop a model that reliably quantifies mRNA synthesis, nuclear export, and nuclear and cytosolic degradation rates on a genome-wide scale. We find that nuclear degradation of polyadenylated mRNA is negligible and nuclear mRNA export is slow, while cytosolic mRNA degradation is comparatively fast. Consequently, an mRNA molecule generally spends most of its life in the nucleus. We also observe large differences in the nuclear export rates of different 3’UTR transcript isoforms. Furthermore, we identify genes whose expression is abruptly induced upon metabolic labeling. These transcripts are exported substantially faster than average mRNAs, suggesting the existence of alternative export pathways. Our results highlight nuclear mRNA export as a limiting factor in mRNA metabolism and gene regulation.
Project description:Alternative polyadenylation (APA) produces mRNA isoforms with different 3’UTR lengths. Previous studied indicated that 3’ end processing and mRNA nuclear export are intertwined in gene regulation. Here, we show that mRNA export factors generally facilitate usage of distal cleavage and polyadenylation sites (PASs), leading to expression of long 3’UTR isoforms. By focusing on the export receptor NXF1, which exhibits the most potent effect on APA in this study, we reveal a number of gene features that impact NXF1-dependent APA, including 3’UTR size, gene size and AT content. Surprisingly, downregulation of NXF1 results in accumulation of RNAP II at the 3’ end of genes, correlating with its role in APA regulation. Moreover, we show that NXF1 cooperates with CFI-68 to facilitate nuclear export of long 3’UTR isoform with UGUA motifs. Together, our work reveals several important roles of NXF1 in coordinating RNAPII distribution, 3’ end processing, and mRNA export of long 3’UTR transcripts, implicating NXF1 as the nexus of gene expression regulation.
Project description:PGC-1α plays a central role in maintaining the mitochondrial and energy metabolism homeostasis, linking external stimuli to the transcriptional co-activation of genes involved in adaptive and age-related pathways. The carboxyl-terminus encodes a serine/arginine-rich (RS) region and a putative RNA recognition motif, however potential RNA-processing role(s) have remained elusive for the past 20 years. Here, we show that the RS domain of human PGC-1α directly interacts with RNA and the nuclear RNA export factor NXF1. Inducible depletion of endogenous PGC-1α and expression of RNAi-resistant RS-deleted PGC-1α further demonstrate that the RNA-binding activity is required for nuclear export of co-activated transcripts and mitochondrial homeostasis. Moreover, a quantitative proteomics approach confirmed PGC-1α-dependent RNA transport and mitochondrial-related functions, identifying also novel mRNA nuclear export targets in age-related telomere maintenance. Discovering a novel function for a major cellular homeostasis regulator provides new directions to further elucidate the roles of PGC-1α in gene expression, metabolic disorders, ageing and neurodegenerative diseases.
Project description:mRNA export is central to gene regulation and expression. In trypanosomes, transcription is polycistronic, all mRNAs are processed by trans-splicing and export is mediated by non-canonical mechanisms. We have described several conserved mRNA export pathway components in Trypanosoma cruzi, including orthologs of Sub2, a component of the TREX complex, and eIF4AIII, a core component of the exon junction complex (EJC). Few orthologs of proteins involved in mRNA export in higher eukaryotes are detectable in trypanosome genomes and examples of mechanistic divergence well known. To uncover additional components of the trypanosome mRNA maturation and export system we undertook an unbiased search for protein interactors of TcSub2 and TceIF4AIII. Significant overlap between TcSub2 and TceIF4AIII interacting protein cohorts suggests that both proteins associate with similar machinery. We confirmed several interactions with conserved core components of the EJC and multiple additional complexes, together with identification of proteins specific to trypanosomatids. The highly interactive super-interactome uncovered here, capable of supporting RNA processing from splicing through to nuclear export and cytoplasmic events, highlights kinetoplastid-specific and conserved components creating an amalgam to support the unique mRNA maturation mechanisms in trypanosomes.