Project description:The processing of Arabidopsis thaliana microRNAs (miRNAs) from longer primary transcripts (pri-miRNAs) requires the activity of several proteins, including DICER-LIKE1 (DCL1), the double stranded RNA binding protein HYPONASTIC LEAVES1 (HYL1), and the zinc finger protein SERRATE (SE). It has been noted before that the morphological appearance of weak se mutants is reminiscent of plants with mutations in ABH1/CBP80 and CBP20, which encode the two subunits of the nuclear cap-binding complex. We report that, like SE, the cap-binding complex is necessary for proper processing of pri-miRNAs. Inactivation of either ABH1/CBP80 or CBP20 results in decreased levels of mature miRNAs accompanied by increased levels of pri-miRNAs. Whole genome tiling array analyses reveal that se, abh1/cbp80 and cbp20 mutants also share similar pre-mRNA splicing defects, leading to the accumulation of many partially spliced transcripts. This is unlikely to be an indirect consequence of improper miRNA processing or other mRNA turnover pathways, since introns retained in se, abh1/cbp80 and cbp20 mutants are not affected by mutations in other genes required for miRNA processing or for non-sense-mediated mRNA decay. Taken together, our results uncover dual roles in splicing and miRNA processing that distinguish SE and the cap-binding complex from specialized miRNA processing factors such as DCL1 and HYL1. Keywords: Tiling array analysis of RNA populations from wild type, se, abh1 and cbp20 mutants
Project description:N6-methyladenosine (m6A) is the most common prevalent internal modifications found in many of the eukaryotic mRNA and plays an important role in RNA metabolism including pre-mRNA processing, mRNA stability, RNA splicing, RNA export and nuclear retention. Serrate is a component of the Dicer complex, plays as a key factor in RNA metabolism. We here reported SERRATE acts as a key regulator of mRNA m6A modification in Arabidopsis. Loss function of SE results in significant global m6A level reduction in the se-1 mutant comparing to the Col-0. SE positively regulates the transcription of MTA and MTB. In addition, SE physically interacts and functionally works with the m6A writer complex MTA and MTB which affects the binding of m6A methylase to mRNA. Taking together, our data provides a molecular framework that SE modulates m6A mRNA modification in Arabidopsis.
Project description:ARS2 is a highly conserved metazoan protein involved in numerous aspects of nuclear RNA metabolism. As a direct partner of the nuclear cap-binding complex (CBC) it mediates interactions with diverse RNA processing and transport machineries in a transcript-dependent manner. Here we present the human ARS2 crystal structure, which exhibits similarities and metazoan-specific differences to the plant homologue SERRATE, most notably an additional RRM domain. We present biochemical, biophysical and cellular interactome data comparing wild type and mutant ARS2 that identify regions critical for interactions with FLASH (involved in histone mRNA biogenesis), NCBP3 (a putative cap-binding protein involved in mRNA export) and single-stranded RNA. We show that FLASH and NCBP3 have overlapping binding sites on ARS2 and that CBC-ARS2-NCBP3 form a ternary complex that is mutually exclusive with CBC-ARS-PHAX (involved in snRNA export). Our results support that mutually exclusive higher order CBC-ARS2 complexes are critical in determining Pol II transcript fate.
Project description:Adaptive response to stress involves an extensive reprogramming of gene expression. Under stressful conditions, the induction of efficient changes in mRNA production is crucial for maximized plant survival. Transcription and pre-mRNA processing are two closely related steps in mRNA biogenesis, yet how they are controlled in plant stress response remains elusive. Here, we show that the Arabidopsis nuclear cap-binding complex (CBC) component CBP20 directly interacts with ELF7, a subunit of the transcription elongation factor RNA Pol II-associated factor 1 complex (PAF1c) to promote RNA Pol II transcription in plant response to salt stress. CBP20 and ELF7 co-regulate the expression of a large number of genes including those crucial for salt tolerance. Both CBP20 and ELF7 are required for enhanced RNA Pol II elongation at salt-activated genes. Though CBP20 also regulates intron splicing, this function is largely independent of ELF7. Our study reveals the function of an RNA processing regulator CBC in assisting efficient RNA Pol II transcription and pinpoints the complex roles of CBC on mRNA production in plant salt stress resistance.
Project description:Gene expression in Eukaryotic cells is profoundly shaped by the post-transcriptional processing of mRNAs, including the splicing of introns in the nucleus and both nuclear and cytoplasmic degradation pathways. Here we report the use of a splicing isoform specific microarray platform to investigate the effects of a host of diverse stress conditions on both splicing pre-mRNA fate. Interestingly, We find that diverse stresses cause distinct patterns of changes at the level of pre- mRNA processing. The responses we observed are most dramatic for the RPGs and can be categorized into three major classes. The first is characterized by accumulation of RPG pre-mRNA and is seen in multiple types of amino acid starvation regimes; the magnitude of splicing inhibition correlates with the severity of the stress. The second class is characterized by a rapid decrease in both pre- and mature RPG mRNA and is seen in many stresses that inactivate the TORC1 kinase complex. These decreases depend on nuclear turn-over of the intron-containing pre-RNAs. The third class is characterized by a decrease in RPG pre-mRNA with only a modest reduction in the mature species; this response is observed in hyperosmotic and cation-toxic stresses. We show that casein kinase 2 (CK2) makes important contributions to the changes in pre-mRNA processing, particularly for the first two classes of stress responses. In total, our data suggest that complex post-transcriptional programs cooperate to fine-tune expression of intron-containing transcripts in budding yeast. Splicing-specific microarrays were used to assay the changes to splicing caused by a wide variety of environmental stresses and nutrient conditions.
Project description:MicroRNAs (miRNAs) play key regulatory roles in numerous developmental and physiological processes in animals and plants. The elaborate mechanism of miRNA biogenesis involves transcription and multiple processing steps. Here, we report the identification of a pair of evolutionarily conserved NOT2_3_5 domain containing proteins, NOT2a and NOT2b (previously known as At-NOT2 and VIP2, respectively), as components involved in Arabidopsis miRNA biogenesis. NOT2 was identified by its interaction with the Piwi/Ago/Zwille (PAZ) domain of Dicer-like 1 (DCL1), an interaction that is conserved between rice and Arabidopsis. Inactivation of both NOT2 genes in Arabidopsis caused severe defects in male gametophytes, and weak lines show pleiotropic defects reminiscent of miRNA pathway mutants. Impairment of NOT2s decreases the accumulation of pri-miRNAs and mature miRNAs and increases DCL1-containing nuclear speckle number in vivo. In addition, NOT2b protein interacts with Pol II and other miRNA processing factors including two cap-binding proteins, CBP80/ABH1, CBP20 and SERRATE (SE). Therefore, these results suggest that NOT2 proteins promote MIR transcription and facilitate efficient DCL1 recruitment in Arabidopsis. Examination of transcriptome of not2 and wild type by RNA-seq.
Project description:Primary telomerase RNA transcripts are processed into shorter mature forms that assemble into a complex with the catalytic subunit and provide the template for telomerase activity. In diverse fungi telomerase RNA 3â end processing involves a single cleavage reaction by the spliceosome akin to the first step of splicing. Longer forms of human telomerase RNA (hTR) have been reported, but how the mature form of precisely 451 nucleotides is generated is still unknown. We now show that the splicing inhibitor isoginkgetin causes accumulation of long hTR transcripts, but find no evidence for a direct role for splicing in hTR processing. Instead, isoginkgetin mimics the effects of inhibiting the RNA exosome. Depletion of exosome components and accessory factors reveals functions for the cap binding complex (CBC) and the nuclear exosome targeting (NEXT) complex in hTR turnover. Whereas longer transcripts are predominantly degraded, shorter precursor RNAs are oligo-adenylated by TRF4-2 and either processed by poly (A) specific ribonuclease (PARN) or degraded by the exosome. Our results reveal that hTR biogenesis involves a kinetic competition between RNA processing and quality control pathways and suggest new treatment options for dyskeratosis congenita caused by mutations in RNA processing factors. We cloned and sequenced 3â ends by RLM-RACE coupled with high-throughput sequencing to gain further insights into hTR processing.
Project description:Dynamic RNA-protein interactions govern the co-transcriptional packaging of RNA polymerase II (RNAPII)-derived transcripts. Yet, our current understanding of this process in vivo primarily stems from steady state analysis. To remedy this, we here conduct temporal-iCLIP (tiCLIP), combining RNAPII transcriptional synchronisation with UV cross-linking of RNA-protein complexes at serial timepoints. We apply tiCLIP to the RNA export adaptor, ALYREF; a component of the Nuclear Exosome Targeting (NEXT) complex, RBM7; and the nuclear cap binding complex (CBC). Regardless of function, all tested factors interact with nascent RNA as it exits RNAPII. Moreover, we demonstrate that the two transesterification steps of pre-mRNA splicing temporally separate ALYREF and RBM7 binding to splicing intermediates, and that exon-exon junction density drives RNA 5’end binding of ALYREF. Finally, we identify underappreciated steps in snoRNA 3’end processing performed by RBM7. Altogether, our data provide an unprecedented temporal view of RNA-protein interactions during the early phases of transcription.
Project description:MicroRNAs (miRNAs) regulate plant development by post-transcriptional regulation of target genes. In Arabidopsis thaliana, DCL1 processes precursors (pri-miRNAs) to miRNA duplexes, which associate with AGO1. Additional proteins act in concert with DCL1 (e.g. HYL1 and SERRATE) or AGO1, respectively, to facilitate efficient and precise pri-miRNA processing and miRNA loading. In this study, we show that the accumulation of plant microRNAs depends on RECEPTOR FOR ACTIVATED C KINASE 1 (RACK1), a scaffold protein found in all higher eukaryotes. miRNA levels are reduced in rack1 mutants and our data suggest that RACK1 affects the microRNA pathway via several distinct mechanisms involving direct interactions with known microRNA factors: RACK1 ensures the accumulation and processing of some pri-miRNAs, directly interacts with SERRATE and is part of an AGO1 complex. As a result, mutations in RACK1 lead to misregulation of miRNA target genes, which is important for ABA responses and phyllotaxy. In conclusion, our study discovered complex functioning of RACK1 proteins in the Arabidopsis miRNA pathway, which are important for miRNA production and therefore plant development.
Project description:We show that in S. cerevisiae pre-snoRNA processing by the endonuclease Rnt1 occurs co-transcriptionally, removing the m7G cap to facilitate the formation of box C/D snoRNA. Failure to remove m7G cap from box C/D pre-snoRNA affects 3’ end processing, ribonucleoprotein complex formation and causes mislocalization to the cytoplasm. Consequently, Rnt1-dependent 5’ end processing of box C/D snoRNA is critical for snoRNA-dependent methylation of ribosomal RNA. Our results reveal that the 5’ end processing defines a distinct pathway for snoRNA maturation.