Project description:N6-methyladenosine (m6A) is the most abundant internal modification of eukaryotic mRNA. This modification has previously been shown to alter the export kinetics for mRNAs though the molecular details surrounding this phenomenon remain poorly understood. Here we show that the m6A complex (WTAP, KIAA1429, METTL3/14) drives recruitment of the TREX mRNA export complex onto m6A modified mRNAs and this process is essential for the efficient export of certain mRNAs. Depletion of the core m6A complex leads to loss of TREX from mRNAs which undergo the m6A modification. We show that TREX stimulates recruitment of the m6A reader protein YTHDC1 to the mRNP and the m6A complex influences the interaction of TREX with YTHDC1. We suggest that m6A acts as a surrogate for other TREX recruitment mechanisms such as splicing and 5’ capping, in long internal and final exons which may otherwise be devoid of this essential complex for mRNA export.
Project description:N6-methyladenosine (m6A) is the most abundant internal modification of eukaryotic mRNA. This modification has previously been shown to alter the export kinetics for mRNAs though the molecular details surrounding this phenomenon remain poorly understood. Recruitment of the TREX mRNA export complex to mRNA is driven by transcription, 5' capping and pre-mRNA splicing. Here we identify a fourth mechanism in human cells driving the association of TREX with mRNA involving the m6A methylase complex. We show that the m6A complex recruits TREX to m6A modified mRNAs and this process is essential for their efficient export. TREX also stimulates recruitment of the m6A reader protein YTHDC1 to the mRNA and the m6A complex influences the interaction of TREX with YTHDC1. Together our studies reveal a key role for TREX in the export of m6A modified mRNAs.
Project description:Transcription termination of mRNAs transcribed from a given locus has a decisive role in regulating the gene function as it determines the coding potential and inclusion of regulatory sequence elements. Failure in appropriate transcription termination leads to read-through transcription, resulting in the synthesis of antisense RNAs which can have profound impact on overall gene expression. However, molecular mechanisms which regulate transcription termination and chimeric RNA formation are poorly understood. We explored the regulatory function of transcription and export complex (THO/TREX) in transcription termination. We show that two members of THO/TREX complex, TREX COMPONENT 1 (TEX1) and HYPER RECOMBINATION1(HPR1) are critical for the correct transcription termination in Arabidopsis. We first demonstrate this by showing defective termination of the bacterial nopaline synthase (NOS) terminator on a transgene in tex1 and hpr1 mutants. Additionally, we show that RNA termination defects in tex1 and hpr1 mutants are widespread at the whole genome levels leading to 3’UTR extensions, truncations and in some cases in the formation of intergenic chimeric transcripts. Chromatin immunoprecipitation coupled with quantitative PCR experiments confirmed the presence of RNA polymerase II beyond the canonical termination sites on genes with defective RNA termination in tex1 and hpr1 mutants. These results demonstrate that THO/TREX complex is a novel regulator of transcription termination in Arabidopsis.
Project description:During gene expression, RNA export factors are mainly known for driving nucleocytoplasmic transport. While early studies suggested that the Exon Junction Complex (EJC) may provide a binding platform for them, subsequent work proposed that they are only recruited by the Cap-Binding Complex (CBC) to the 5’ end of RNAs, as part of the TREX complex. Using iCLIP, we show that the export receptor Nxf1 and two TREX subunits, Alyref and Chtop, are actually recruited to the whole mRNA co-transcriptionally via splicing but before 3’-end processing. Consequently, Alyref can alter splicing decisions and Chtop regulates alternative polyadenylation. Surprisingly, we observe that eIF4A3 stimulates Alyref deposition on single exon or spliced RNAs close to EJC sites. Additional experiments suggest that Alyref is recruited to the 5’-end of RNAs by CBC before binding RNAs near EJCs. Our study reveals mechanical insights into the co-transcriptional recruitment of mRNA export factors and how this shapes the human transcriptome.
Project description:During gene expression, RNA export factors are mainly known for driving nucleocytoplasmic transport. While early studies suggested that the Exon Junction Complex (EJC) may provide a binding platform for them, subsequent work proposed that they are only recruited by the Cap-Binding Complex (CBC) to the 5’ end of RNAs, as part of the TREX complex. Using iCLIP, we show that the export receptor Nxf1 and two TREX subunits, Alyref and Chtop, are actually recruited to the whole mRNA co-transcriptionally via splicing but before 3’-end processing. Consequently, Alyref can alter splicing decisions and Chtop regulates alternative polyadenylation. Surprisingly, we observe that eIF4A3 stimulates Alyref deposition on single exon or spliced RNAs close to EJC sites. Additional experiments suggest that Alyref is recruited to the 5’-end of RNAs by CBC before binding RNAs near EJCs. Our study reveals mechanical insights into the co-transcriptional recruitment of mRNA export factors and how this shapes the human transcriptome.
Project description:Nuclear pore complexes (NPCs) influence gene expression besides their established function in nuclear transport. The TREX-2 complex localizes to the NPC basket and affects gene-NPC interactions, transcription and mRNA export. How TREX-2 regulates the gene expression machinery is unknown. Here, we show that TREX-2 interacts with the Mediator complex, an essential regulator of RNA Polymerase (Pol) II. Structural and biochemical studies identify a conserved region on TREX-2, which directly binds the Mediator Med31/Med7N submodule. TREX-2 regulates assembly of Mediator with its Cdk8 kinase and is required for recruitment and site-specific phosphorylation of Pol II. Transcriptome and phenotypic profiling confirm that TREX-2 and Med31 are functionally interdependent. TREX-2 additionally uses its Mediator-interacting surface to regulate mRNA export suggesting a mechanism for coupling transcription initiation and early steps of mRNA processing at the Mediator level. In sum, we provide insight into how NPC-associated adaptor complexes can access the core transcription machinery. RNAseq was performed from WT, sac3∆, cdk8∆ and Sac3 R288D mutant cells. For each strain triplicates were analyzed. WT strain was sac3∆ transformed with pRS315 SAC3 WT
Project description:Unlike in metazoans, the stepwise biogenesis of microRNAs (miRNAs) occurs within the nucleus in plants. Whether or how the major steps in miRNA biogenesis are coordinated is largely unknown. Here, we show that the plant TREX-2 complex promotes multiple steps in miRNA biogenesis, including transcription, processing and nuclear export. Core subunits of TREX-2, THP1 and SAC3A, interact and co-localize with RNA Polymerase II to promote the transcription of MIR genes in the nucleoplasm. TREX-2 interacts with the microprocessor component SERRATE and promotes the formation of Dicing bodies in the nucleoplasm. THP1 also interacts and co-localizes with a nucleoporin protein NUP1 at the nuclear envelope. NUP1 and THP1 promote the nuclear export of miRNAs and AGO1. These results suggest that TREX-2 coordinates the transcription, processing and export steps in miRNA biogenesis to ensure efficient miRNA production.
Project description:Unlike in metazoans, the stepwise biogenesis of microRNAs (miRNAs) occurs within the nucleus in plants. Whether or how the major steps in miRNA biogenesis are coordinated is largely unknown. Here, we show that the plant TREX-2 complex promotes multiple steps in miRNA biogenesis, including transcription, processing and nuclear export. Core subunits of TREX-2, THP1 and SAC3A, interact and co-localize with RNA Polymerase II to promote the transcription of MIR genes in the nucleoplasm. TREX-2 interacts with the microprocessor component SERRATE and promotes the formation of Dicing bodies in the nucleoplasm. THP1 also interacts and co-localizes with a nucleoporin protein NUP1 at the nuclear envelope. NUP1 and THP1 promote the nuclear export of miRNAs and AGO1. These results suggest that TREX-2 coordinates the transcription, processing and export steps in miRNA biogenesis to ensure efficient miRNA production.
Project description:THO/TREX is a conserved nuclear complex that functions in mRNP biogenesis at the interface of transcription-RNA export with a key role in preventing transcription-associated genome instability. We used microarrays to analyze the impact of different THO/TREX mutations on gene expression and found that THO-Sub2 deletions have a high functional impact on highly expressed, long and G+C-rich genes regardless of gene function. S. cerevisiae strains were grown in YPAD liquid culture, total RNA was isolated and hybridized on Affymetrix microarrays.