Project description:The nuclear cap-binding complex (CBC) stimulates multiple steps in several RNA maturation pathways, but how it functions in humans is incompletely understood. For small capped RNAs like pre-snRNAs, the CBC recruits PHAX. Here, we identify the CBCAP complex, composed of CBC, Ars2 and PHAX, and show that both CBCAP and CBC-Ars2 complexes can be reconstituted from recombinant proteins. Ars2 stimulates PHAX binding to the CBC as well as snRNAs 3'-end processing, hereby coupling maturation with export. In vivo, CBC and Ars2 bind similar capped non-coding and coding RNAs, and stimulate their 3M-bM-^@M-^Y-end processing. Strongest effects are displayed for cap-proximal polyadenylation sites, thereby favoring premature transcription termination. Ars2 functions in part through the mRNA 3M-bM-^@M-^Y-end cleavage factor CLP1, which binds RNA Polymerase II through PCF11. Ars2 is thus a major CBC effector that stimulates functional and cryptic 3'-end processing sites. In total 12 samples; 4 control IP, 2 Flag- Ars2 IP and 2 Flag-CBP20 IP; 2 control FFL siRNA and 2 siRNA Ars2
Project description:The nuclear cap-binding complex (CBC) stimulates multiple steps in several RNA maturation pathways, but how it functions in humans is incompletely understood. For small capped RNAs like pre-snRNAs, the CBC recruits PHAX. Here, we identify the CBCAP complex, composed of CBC, Ars2 and PHAX, and show that both CBCAP and CBC-Ars2 complexes can be reconstituted from recombinant proteins. Ars2 stimulates PHAX binding to the CBC as well as snRNAs 3'-end processing, hereby coupling maturation with export. In vivo, CBC and Ars2 bind similar capped non-coding and coding RNAs, and stimulate their 3’-end processing. Strongest effects are displayed for cap-proximal polyadenylation sites, thereby favoring premature transcription termination. Ars2 functions in part through the mRNA 3’-end cleavage factor CLP1, which binds RNA Polymerase II through PCF11. Ars2 is thus a major CBC effector that stimulates functional and cryptic 3'-end processing sites.
Project description:The nuclear cap-binding complex (CBC) stimulates processing reactions of capped RNAs, including their splicing, 3'-end formation, degradation, and transport. CBC effects are particular for individual RNA families, but how such selectivity is achieved remains elusive. Here, we analyze three main CBC partners known to impact different RNA species. ARS2 stimulates 3'-end formation/transcription termination of several transcript types, ZC3H18 stimulates degradation of a diverse set of RNAs, and PHAX functions in pre-small nuclear RNA/small nucleolar RNA (pre-snRNA/snoRNA) transport. Surprisingly, these proteins all bind capped RNAs without strong preferences for given transcripts, and their steady-state binding correlates poorly with their function. Despite this, PHAX and ZC3H18 compete for CBC binding and we demonstrate that this competitive binding is functionally relevant. We further show that CBC-containing complexes are short lived in vivo, and we therefore suggest that RNA fate involves the transient formation of mutually exclusive CBC complexes, which may only be consequential at particular checkpoints during RNA biogenesis.
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.
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:Nuclear processing and quality control of eukaryotic RNA is mediated by the multi-subunit RNA exosome, which utilizes accessory factors to regulate its enzymatic activity. However, the mechanism of exosome recruitment to its ribonucleoprotein (RNP) targets remains poorly understood. Here we disclose a physical link between the human nuclear RNA exosome and the cap-binding complex (CBC). The CBC associates with the ARS2 protein to form CBC-ARS2 (CBCA), and then further connects together with the uncharacterized ZC3H18/NHN1 protein to the nuclear exosome targeting (NEXT) complex, forming CBC-NEXT (CBCN). RNA immunoprecipitation analysis using CBCN factors as baits as well as the combinatorial depletion of CBCN and exosome components underscore the functional relevance of CBC-exosome bridging at the level of target RNA. Specifically, CBCA suppresses read-through transcription of several RNA families by promoting their transcriptional termination. We suggest that the RNP 5’cap links transcription termination to exosomal RNA degradation via CBCN.
Project description:Nuclear processing and quality control of eukaryotic RNA is mediated by the multi-subunit RNA exosome, which utilizes accessory factors to regulate its enzymatic activity. However, the mechanism of exosome recruitment to its ribonucleoprotein (RNP) targets remains poorly understood. Here we disclose a physical link between the human nuclear RNA exosome and the cap-binding complex (CBC). The CBC associates with the ARS2 protein to form CBC-ARS2 (CBCA), and then further connects together with the uncharacterized ZC3H18/NHN1 protein to the nuclear exosome targeting (NEXT) complex, forming CBC-NEXT (CBCN). RNA immunoprecipitation analysis using CBCN factors as baits as well as the combinatorial depletion of CBCN and exosome components underscore the functional relevance of CBC-exosome bridging at the level of target RNA. Specifically, CBCA suppresses read-through transcription of several RNA families by promoting their transcriptional termination. We suggest that the RNP 5M-bM-^@M-^Ycap links transcription termination to exosomal RNA degradation via CBCN. In total 10 samples; 4 control IP HeLa, 2 Flag- Ars2 IP, 2 Flag-CBP20 IP; and 2 GFP-RBM7 Ips. The signal intensity data was analyzed with the Affymetrix Tiling Analysis Software (v. 1.1) using parameters: one side upper, 90 bp bandwidth and perfect match only. Output txt files (i.e. result file). TASParam* files include parameter settings and input file information for the TAS analysis for each result file. The description of 'ProcessedDatas_TA.xls' file is provided in the 'README.txt'
Project description:Competing exonucleases that promote 3’ end maturation or degradation direct quality control of small non-coding RNAs, but how these enzymes distinguish normal from aberrant RNAs is poorly understood. The Pontocerebellar Hypoplasia 7 (PCH7)-associated 3’ exonuclease TOE1 promotes maturation of canonical small nuclear RNAs (snRNAs). Here, we demonstrate that TOE1 achieves specificity towards canonical snRNAs by recognizing Sm complex assembly and cap trimethylation, two features that distinguish snRNAs undergoing correct biogenesis from other small non-coding RNAs. Indeed, disruption of Sm complex assembly via snRNA mutations or protein depletions obstructs snRNA processing by TOE1, and in vitro snRNA processing by TOE1 is stimulated by a trimethylated cap. An unstable snRNA variant that normally fails to undergo maturation becomes fully processed by TOE1 when its degenerate Sm binding motif is converted into a canonical one. Our findings uncover the molecular basis for how TOE1 distinguishes snRNAs from other small non-coding RNAs and explain how TOE1 promotes maturation specifically of canonical snRNAs undergoing proper processing.
Project description:Competing exonucleases that promote 3’ end maturation or degradation direct quality control of small non-coding RNAs, but how these enzymes distinguish normal from aberrant RNAs is poorly understood. The Pontocerebellar Hypoplasia 7 (PCH7)-associated 3’ exonuclease TOE1 promotes maturation of canonical small nuclear RNAs (snRNAs). Here, we demonstrate that TOE1 achieves specificity towards canonical snRNAs by recognizing Sm complex assembly and cap trimethylation, two features that distinguish snRNAs undergoing correct biogenesis from other small non-coding RNAs. Indeed, disruption of Sm complex assembly via snRNA mutations or protein depletions obstructs snRNA processing by TOE1, and in vitro snRNA processing by TOE1 is stimulated by a trimethylated cap. An unstable snRNA variant that normally fails to undergo maturation becomes fully processed by TOE1 when its degenerate Sm binding motif is converted into a canonical one. Our findings uncover the molecular basis for how TOE1 distinguishes snRNAs from other small non-coding RNAs and explain how TOE1 promotes maturation specifically of canonical snRNAs undergoing proper processing.
Project description:Ars2 is a component of the nuclear cap-binding complex that is required for cellular proliferation and contributes to microRNA biogenesis. Arrays were performed to determine the repertoire of genes that change following knock-down of Ars2. Knock-down of DGCR8 was also performed to determine which changes in Ars2 knock-down cells resulted from defects in microRNA expression. 9 samples were analyzed including: three biological replicates of control siRNA-transfected HeLa cells, HeLa cells transfected with three independent siRNAs targeting Ars2, or HeLa cells transfected with three independent siRNAs targeting DGCR8.