RESUMO
In general, mRNAs are assumed to be loaded with ribosomes instantly upon entry into the cytoplasm. To measure ribosome density (RD) on nascent mRNA, we developed nascent Ribo-Seq by combining Ribo-Seq with progressive 4-thiouridine labeling. In mouse macrophages, we determined experimentally the lag between the appearance of nascent mRNA and its association with ribosomes, which was calculated to be 20-22 min for bulk mRNA. In mouse embryonic stem cells, nRibo-Seq revealed an even stronger lag of 35-38 min in ribosome loading. After stimulation of macrophages with lipopolysaccharide, the lag between cytoplasmic and translated mRNA leads to uncoupling between input and ribosome-protected fragments, which gives rise to distorted RD measurements under conditions where mRNA amounts are far from steady-state expression. As a result, we demonstrate that transcriptional changes affect RD in a passive way.
Assuntos
Biossíntese de Proteínas , Ribossomos/genética , Ribossomos/metabolismo , Análise de Sequência de RNA/métodos , Animais , Citoplasma/genética , Cinética , Lipopolissacarídeos/farmacologia , Camundongos , Células-Tronco Embrionárias Murinas/citologia , Células-Tronco Embrionárias Murinas/fisiologia , Células RAW 264.7 , RNA Mensageiro/genética , Proteínas Ribossômicas/biossíntese , Proteínas Ribossômicas/genética , Ribossomos/efeitos dos fármacos , Fatores de TempoRESUMO
The transcription factor p53 exerts its tumour suppressive effect through transcriptional activation of numerous target genes controlling cell cycle arrest, apoptosis, cellular senescence and DNA repair. In addition, there is evidence that p53 influences the translation of specific mRNAs, including translational inhibition of ribosomal protein synthesis and translational activation of MDM2. A challenge in the analysis of translational control is that changes in mRNA abundance exert a kinetic (passive) effect on ribosome densities. In order to separate these passive effects from active regulation of translation efficiency in response to p53 activation, we conducted a comprehensive analysis of translational regulation by comparative analysis of mRNA levels and ribosome densities upon DNA damage induced by neocarzinostatin in wild-type and TP53-/- HCT116 colorectal carcinoma cells. Thereby, we identified a specific group of mRNAs that are preferentially translated in response to p53 activation, many of which correspond to p53 target genes including MDM2, SESN1 and CDKN1A. By subsequent polysome profile analysis of SESN1 and CDKN1A mRNA, we could demonstrate that p53-dependent translational activation relies on a combination of inducing the expression of translationally advantageous isoforms and trans-acting mechanisms that further enhance the translation of these mRNAs.
Assuntos
Ribossomos , Proteína Supressora de Tumor p53 , Pontos de Checagem do Ciclo Celular , Regulação da Expressão Gênica , Humanos , RNA Mensageiro/genética , RNA Mensageiro/metabolismo , Ribossomos/genética , Ribossomos/metabolismo , Fatores de Transcrição/metabolismo , Proteína Supressora de Tumor p53/genética , Proteína Supressora de Tumor p53/metabolismoRESUMO
RNA polymerase (Pol) III is responsible for the transcription of genes encoding small RNAs, including tRNA, 5S rRNA and U6 RNA. Here, we report the electron cryomicroscopy structures of yeast Pol III at 9.9 Å resolution and its elongation complex at 16.5 Å resolution. Particle sub-classification reveals prominent EM densities for the two Pol III-specific subcomplexes, C31/C82/C34 and C37/C53, that can be interpreted using homology models. While the winged-helix-containing C31/C82/C34 subcomplex initiates transcription from one side of the DNA-binding cleft, the C37/C53 subcomplex accesses the transcription bubble from the opposite side of this cleft. The transcribing Pol III enzyme structure not only shows the complete incoming DNA duplex, but also reveals the exit path of newly synthesized RNA. During transcriptional elongation, the Pol III-specific subcomplexes tightly enclose the incoming DNA duplex, which likely increases processivity and provides structural insights into the conformational switch between Pol III-mediated initiation and elongation.
Assuntos
RNA Polimerase III/química , Saccharomyces cerevisiae/enzimologia , Microscopia Crioeletrônica , Modelos Moleculares , Conformação Proteica , Multimerização Proteica , Estrutura Terciária de Proteína , RNA Polimerase III/genética , Saccharomyces cerevisiae/química , Saccharomyces cerevisiae/genética , Homologia Estrutural de Proteína , Transcrição GênicaRESUMO
The integrated stress response (ISR) is a key cellular signaling pathway activated by environmental alterations that represses protein synthesis to restore homeostasis. To prevent sustained damage, the ISR is counteracted by the upregulation of growth arrest and DNA damage-inducible 34 (GADD34), a stress-induced regulatory subunit of protein phosphatase 1 that mediates translation reactivation and stress recovery. Here, we uncover a novel ISR regulatory mechanism that post-transcriptionally controls the stability of PPP1R15A mRNA encoding GADD34. We establish that the 3' untranslated region of PPP1R15A mRNA contains an active AU-rich element (ARE) recognized by proteins of the ZFP36 family, promoting its rapid decay under normal conditions and stabilization for efficient expression of GADD34 in response to stress. We identify the tight temporal control of PPP1R15A mRNA turnover as a component of the transient ISR memory, which sets the threshold for cellular responsiveness and mediates adaptation to repeated stress conditions.
Assuntos
Regiões 3' não Traduzidas , Proteína Fosfatase 1 , Animais , Humanos , Camundongos , Regiões 3' não Traduzidas/genética , Adaptação Fisiológica/genética , Elementos Ricos em Adenilato e Uridilato/genética , Células HEK293 , Proteína Fosfatase 1/metabolismo , Proteína Fosfatase 1/genética , Estabilidade de RNA/genética , RNA Mensageiro/metabolismo , RNA Mensageiro/genética , Estresse Fisiológico/genética , Tristetraprolina/metabolismo , Tristetraprolina/genéticaRESUMO
Polycomb group (PcG) proteins repress transcription by modifying chromatin structure in target genes. dSfmbt is a subunit of the Drosophila melanogaster PcG protein complex PhoRC and contains four malignant brain tumour (MBT) repeats involved in the recognition of various mono- and dimethylated histone peptides. Here, we present the crystal structure of the four-MBT-repeat domain of dSfmbt in complex with a mono-methylated histone H4 peptide. Only a single histone peptide binds to the four-MBT-repeat domain. Mutational analyses show high-affinity binding with low peptide sequence selectivity through combinatorial interaction of the methyl-lysine with an aromatic cage and positively charged flanking residues with the surrounding negatively charged surface of the fourth MBT repeat. dSfmbt directly interacts with the PcG protein Scm, a related MBT-repeat protein with similar methyl-lysine binding activity. dSfmbt and Scm co-occupy Polycomb response elements of target genes in Drosophila and they strongly synergize in the repression of these target genes, suggesting that the combined action of these two MBT proteins is crucial for Polycomb silencing.
Assuntos
Proteínas de Drosophila/química , Proteínas de Drosophila/metabolismo , Histonas/química , Histonas/metabolismo , Lisina/metabolismo , Proteínas Repressoras/química , Proteínas Repressoras/metabolismo , Sequência de Aminoácidos , Animais , Sítios de Ligação , Cristalografia por Raios X , Proteínas de Drosophila/genética , Drosophila melanogaster/genética , Drosophila melanogaster/metabolismo , Histonas/genética , Humanos , Lisina/química , Metilação , Modelos Moleculares , Dados de Sequência Molecular , Mutação Puntual , Complexo Repressor Polycomb 1 , Proteínas do Grupo Polycomb , Ligação Proteica , Estrutura Terciária de Proteína , Proteínas Repressoras/genética , Alinhamento de SequênciaRESUMO
Current models posit that nuclear speckles (NSs) serve as reservoirs of splicing factors and facilitate posttranscriptional mRNA processing. Here, we discovered that ribotoxic stress induces a profound reorganization of NSs with enhanced recruitment of factors required for splice-site recognition, including the RNA-binding protein TIAR, U1 snRNP proteins and U2-associated factor 65, as well as serine 2 phosphorylated RNA polymerase II. NS reorganization relies on the stress-activated p38 mitogen-activated protein kinase (MAPK) pathway and coincides with splicing activation of both pre-existing and newly synthesized pre-mRNAs. In particular, ribotoxic stress causes targeted excision of retained introns from pre-mRNAs of immediate early genes (IEGs), whose transcription is induced during the stress response. Importantly, enhanced splicing of the IEGs ZFP36 and FOS is accompanied by relocalization of the corresponding nuclear mRNA foci to NSs. Our study reveals NSs as a dynamic compartment that is remodeled under stress conditions, whereby NSs appear to become sites of IEG transcription and efficient cotranscriptional splicing.
Assuntos
Genes Precoces , Salpicos Nucleares , Splicing de RNA , Íntrons , Ribonucleoproteína Nuclear Pequena U1/genética , Ribonucleoproteína Nuclear Pequena U1/metabolismo , Precursores de RNA/genética , Precursores de RNA/metabolismo , RNA Mensageiro/genética , RNA Mensageiro/metabolismo , HumanosRESUMO
Drosophila Nurf55 is a component of different chromatin-modifying complexes, including the PRC2 (Polycomb repressive complex 2). Based on the 1.75-Å crystal structure of Nurf55 bound to histone H4 helix 1, we analyzed interactions of Nurf55 (Nurf55 or p55 in fly and RbAp48/46 in human) with the N-terminal tail of histone H3, the first helix of histone H4, and an N-terminal fragment of the PRC2 subunit Su(z)12 using isothermal calorimetry and pulldown experiments. Site-directed mutagenesis identified the binding site of histone H3 at the top of the Nurf55 WD40 propeller. Unmodified or K9me3- or K27me3-containing H3 peptides were bound with similar affinities, whereas the affinity for K4me3-containing H3 peptides was reduced. Helix 1 of histone H4 and Su(z)12 bound to the edge of the ß-propeller using overlapping binding sites. Our results show similarities in the recognition of histone H4 and Su(z)12 and identify Nurf55 as a versatile interactor that simultaneously contacts multiple partners.
Assuntos
Proteínas de Drosophila/química , Histona-Lisina N-Metiltransferase/química , Histonas/química , Proteínas Repressoras/química , Proteína 4 de Ligação ao Retinoblastoma/química , Animais , Sítios de Ligação , Cristalografia por Raios X , Proteínas de Drosophila/genética , Proteínas de Drosophila/metabolismo , Drosophila melanogaster , Histona-Lisina N-Metiltransferase/genética , Histona-Lisina N-Metiltransferase/metabolismo , Histonas/genética , Histonas/metabolismo , Complexo Repressor Polycomb 2 , Proteínas do Grupo Polycomb , Estrutura Secundária de Proteína , Proteínas Repressoras/genética , Proteínas Repressoras/metabolismo , Proteína 4 de Ligação ao Retinoblastoma/genética , Proteína 4 de Ligação ao Retinoblastoma/metabolismoRESUMO
BACKGROUND: Cytoplasmic polyadenylation element-binding protein 4 (CPEB4) is known to associate with cytoplasmic polyadenylation elements (CPEs) located in the 3' untranslated region (UTR) of specific mRNAs and assemble an activator complex promoting the translation of target mRNAs through cytoplasmic polyadenylation. RESULTS: Here, we find that CPEB4 is part of an alternative repressor complex that mediates mRNA degradation by associating with the evolutionarily conserved CCR4-NOT deadenylase complex. We identify human CPEB4 as an RNA-binding protein (RBP) with enhanced association to poly(A) RNA upon inhibition of class I histone deacetylases (HDACs), a condition known to cause widespread degradation of poly(A)-containing mRNA. Photoactivatable ribonucleoside-enhanced crosslinking and immunoprecipitation (PAR-CLIP) analysis using endogenously tagged CPEB4 in HeLa cells reveals that CPEB4 preferentially binds to the 3'UTR of immediate early gene mRNAs, at G-containing variants of the canonical U- and A-rich CPE located in close proximity to poly(A) sites. By transcriptome-wide mRNA decay measurements, we find that the strength of CPEB4 binding correlates with short mRNA half-lives and that loss of CPEB4 expression leads to the stabilization of immediate early gene mRNAs. Akin to CPEB4, we demonstrate that CPEB1 and CPEB2 also confer mRNA instability by recruitment of the CCR4-NOT complex. CONCLUSIONS: While CPEB4 was previously known for its ability to stimulate cytoplasmic polyadenylation, our findings establish an additional function for CPEB4 as the RNA adaptor of a repressor complex that enhances the degradation of short-lived immediate early gene mRNAs.
Assuntos
Genes Precoces , Estabilidade de RNA , Regiões 3' não Traduzidas , Células HeLa , Humanos , RNA Mensageiro/genética , RNA Mensageiro/metabolismo , Proteínas de Ligação a RNA/genética , Proteínas de Ligação a RNA/metabolismoRESUMO
The CCR4-NOT complex acts as a central player in the control of mRNA turnover and mediates accelerated mRNA degradation upon HDAC inhibition. Here, we explored acetylation-induced changes in the composition of the CCR4-NOT complex by purification of the endogenously tagged scaffold subunit NOT1 and identified RNF219 as an acetylation-regulated cofactor. We demonstrate that RNF219 is an active RING-type E3 ligase which stably associates with CCR4-NOT via NOT9 through a short linear motif (SLiM) embedded within the C-terminal low-complexity region of RNF219. By using a reconstituted six-subunit human CCR4-NOT complex, we demonstrate that RNF219 inhibits deadenylation through the direct interaction of the α-helical SLiM with the NOT9 module. Transcriptome-wide mRNA half-life measurements reveal that RNF219 attenuates global mRNA turnover in cells, with differential requirement of its RING domain. Our results establish RNF219 as an inhibitor of CCR4-NOT-mediated deadenylation, whose loss upon HDAC inhibition contributes to accelerated mRNA turnover.
Assuntos
RNA Mensageiro/metabolismo , Receptores CCR4/metabolismo , Fatores de Transcrição/metabolismo , Ubiquitina-Proteína Ligases/metabolismo , Monofosfato de Adenosina/metabolismo , Células HeLa , Humanos , Ligação Proteica , Estabilidade de RNA , RNA Mensageiro/química , RNA Mensageiro/genética , Receptores CCR4/genética , Fatores de Transcrição/genética , Ubiquitina-Proteína Ligases/genéticaRESUMO
Cell proliferation exerts a high demand on protein synthesis, yet the mechanisms coupling the two processes are not fully understood. A kinase and phosphatase screen for activators of translation, based on the formation of stress granules in human cells, revealed cell cycle-associated kinases as major candidates. CDK1 was identified as a positive regulator of global translation, and cell synchronization experiments showed that this is an extramitotic function of CDK1. Different pathways including eIF2α, 4EBP, and S6K1 signaling contribute to controlling global translation downstream of CDK1. Moreover, Ribo-Seq analysis uncovered that CDK1 exerts a particularly strong effect on the translation of 5'TOP mRNAs, which includes mRNAs encoding ribosomal proteins and several translation factors. This effect requires the 5'TOP mRNA-binding protein LARP1, concurrent to our finding that LARP1 phosphorylation is strongly dependent on CDK1. Thus, CDK1 provides a direct means to couple cell proliferation with biosynthesis of the translation machinery and the rate of protein synthesis.
Assuntos
Proteína Quinase CDC2/metabolismo , Proliferação de Células , Neoplasias do Colo do Útero/enzimologia , Proteínas Adaptadoras de Transdução de Sinal/genética , Proteínas Adaptadoras de Transdução de Sinal/metabolismo , Animais , Autoantígenos/genética , Autoantígenos/metabolismo , Proteína Quinase CDC2/genética , Proteínas de Ciclo Celular/genética , Proteínas de Ciclo Celular/metabolismo , Fator de Iniciação 2 em Eucariotos/genética , Fator de Iniciação 2 em Eucariotos/metabolismo , Fatores de Iniciação em Eucariotos/genética , Fatores de Iniciação em Eucariotos/metabolismo , Feminino , Fibroblastos/enzimologia , Regulação Enzimológica da Expressão Gênica , Células HEK293 , Células HeLa , Humanos , Cinética , Camundongos Endogâmicos C57BL , Fosforilação , Biossíntese de Proteínas , Sequência de Oligopirimidina na Região 5' Terminal do RNA , RNA Mensageiro/genética , RNA Mensageiro/metabolismo , Ribonucleoproteínas/genética , Ribonucleoproteínas/metabolismo , Proteínas Quinases S6 Ribossômicas 70-kDa/genética , Proteínas Quinases S6 Ribossômicas 70-kDa/metabolismo , Transdução de Sinais , Neoplasias do Colo do Útero/genética , Neoplasias do Colo do Útero/patologia , Antígeno SS-BRESUMO
The mitotic kinases Aurora-A and Aurora-B have similar amino-acid sequences but are differently localised and regulated during cell division. The basis for their interactions with different and specific regulators is unclear. Surprisingly, our recent structural studies indicate that TPX2 regulates Aurora-A activity by binding at a site that is conserved almost completely on Aurora-B. Here we investigate molecular determinants of TPX2-Aurora-A recognition. Using structure-based mutagenesis, we show that a single amino-acid difference on the surface of the kinase catalytic domain is key to the precision with which TPX2 discriminates between Aurora-A and Aurora-B. The conservation at this amino-acid position suggests that this discriminatory mechanism is likely to be conserved in higher eukaryotes.
Assuntos
Proteínas de Ciclo Celular/metabolismo , Proteínas Associadas aos Microtúbulos/metabolismo , Proteínas de Neoplasias/metabolismo , Proteínas Nucleares/metabolismo , Fosfoproteínas/metabolismo , Proteínas Quinases/metabolismo , Proteínas Serina-Treonina Quinases/metabolismo , Animais , Aurora Quinase B , Aurora Quinases , Domínio Catalítico , Drosophila , Ativação Enzimática , Glutationa Transferase/metabolismo , Células HeLa , Humanos , Metáfase , Microtúbulos/metabolismo , Mitose , Modelos Biológicos , Modelos Moleculares , Mutação , Peptídeos/química , Fosforilação , Estrutura Terciária de Proteína , Fuso Acromático/metabolismo , Proteínas de XenopusRESUMO
RNA polymerases are essential enzymes which transcribe DNA into RNA. Here, we obtain mass spectra of the cellular forms of apo and holo eukaryotic RNA polymerase I and III, defining their composition under different solution conditions. By recombinant expression of subunits within the initiation heterotrimer of Pol III, we derive an interaction network and couple this data with ion mobility data to define topological restraints. Our data agree with available structural information and homology modeling and are generally consistent with yeast two hybrid data. Unexpectedly, elongation complexes of both Pol I and III destabilize the assemblies compared with their apo counterparts. Increasing the pH and ionic strength of apo and holo forms of Pol I and Pol III leads to formation of at least ten stable subcomplexes for both enzymes. Uniquely for Pol III many subcomplexes contain only one of the two largest catalytic subunits. We speculate that these stable subcomplexes represent putative intermediates in assembly pathways.
Assuntos
RNA Polimerase III/química , RNA Polimerase I/química , Proteínas de Saccharomyces cerevisiae/química , Saccharomyces cerevisiae/enzimologia , Apoenzimas/química , Polidesoxirribonucleotídeos/química , Multimerização Proteica/efeitos dos fármacos , Estabilidade Proteica , Estrutura Quaternária de Proteína , Estrutura Terciária de Proteína , Espectrometria de Massas por Ionização por Electrospray/métodosRESUMO
Exosomes are complexes containing 3' --> 5' exoribonucleases that have important roles in processing, decay and quality control of various RNA molecules. Archaeal exosomes consist of a hexameric core of three active RNase PH subunits (ribosomal RNA processing factor (Rrp)41) and three inactive RNase PH subunits (Rrp42). A trimeric ring of subunits with putative RNA-binding domains (Rrp4/cep1 synthetic lethality (Csl)4) is positioned on top of the hexamer on the opposite side to the RNA degrading sites. Here, we present the 1.6 A resolution crystal structure of the nine-subunit exosome of Sulfolobus solfataricus and the 2.3 A structure of this complex bound to an RNA substrate designed to be partly trimmed rather than completely degraded. The RNA binds both at the active site on one side of the molecule and on the opposite side in the narrowest constriction of the central channel. Multiple substrate-binding sites and the entrapment of the substrate in the central channel provide a rationale for the processive degradation of extended RNAs and the stalling of structured RNAs.
Assuntos
Proteínas Arqueais/metabolismo , Exorribonucleases/química , Exorribonucleases/metabolismo , Complexos Multienzimáticos/metabolismo , RNA Arqueal/metabolismo , Sulfolobus solfataricus/enzimologia , Proteínas Arqueais/química , Sítios de Ligação , Cristalografia por Raios X , Manganês/metabolismo , Modelos Moleculares , Complexos Multienzimáticos/química , Estrutura Quaternária de Proteína , RNA Ribossômico , Sulfolobus solfataricus/genéticaRESUMO
The chromosomal passenger complex (CPC) is a key regulator of chromosome segregation and cytokinesis. CPC functions are connected to its localization. The complex first localizes to centromeres and later associates with the central spindle and midbody. Survivin, Borealin, and INCENP are the three components of the CPC that regulate the activity and localization of its enzymatic component, the kinase Aurora B. We determined the 1.4 A resolution crystal structure of the regulatory core of the CPC, revealing that Borealin and INCENP associate with the helical domain of Survivin to form a tight three-helical bundle. We used siRNA rescue experiments with structure-based mutants to explore the requirements for CPC localization. We show that the intertwined structural interactions of the core components lead to functional interdependence. Association of the core "passenger" proteins creates a single structural unit, whose composite molecular surface presents conserved residues essential for central spindle and midbody localization.
Assuntos
Proteínas de Ciclo Celular/química , Proteínas Cromossômicas não Histona/química , Segregação de Cromossomos/fisiologia , Proteínas Associadas aos Microtúbulos/química , Proteínas de Neoplasias/química , Fuso Acromático/fisiologia , Sequência de Aminoácidos , Aurora Quinase B , Aurora Quinases , Proteínas de Ciclo Celular/genética , Proteínas de Ciclo Celular/fisiologia , Centrômero/genética , Centrômero/fisiologia , Proteínas Cromossômicas não Histona/genética , Proteínas Cromossômicas não Histona/fisiologia , Segregação de Cromossomos/genética , Citocinese , Dimerização , Células HeLa , Humanos , Proteínas Inibidoras de Apoptose , Proteínas Associadas aos Microtúbulos/genética , Proteínas Associadas aos Microtúbulos/fisiologia , Modelos Moleculares , Dados de Sequência Molecular , Mutação , Proteínas de Neoplasias/genética , Proteínas de Neoplasias/fisiologia , Ligação Proteica , Proteínas Serina-Treonina Quinases/química , Proteínas Serina-Treonina Quinases/genética , Proteínas Serina-Treonina Quinases/fisiologia , Proteínas Recombinantes/química , Proteínas Recombinantes/genética , Proteínas Recombinantes/metabolismo , Fuso Acromático/genética , SurvivinaRESUMO
Cse1 mediates nuclear export of importin alpha, the nuclear localization signal (NLS) import adaptor. We report the 3.1 A resolution structure of cargo-free Cse1, representing this HEAT repeat protein in its cytosolic state. Cse1 is compact, consisting of N- and C-terminal arches that interact to form a ring. Comparison with the structure of cargo-bound Cse1 shows a major conformational change leading to opening of the structure upon cargo binding. The largest structural changes occur within a hinge region centered at HEAT repeat 8. This repeat contains a conserved insertion that connects the RanGTP and importin alpha contact sites and that is essential for binding. In the cargo-free state, the RanGTP binding sites are occluded and the importin alpha sites are distorted. Mutations that destabilize the N- to C-terminal interaction uncouple importin alpha and Ran binding, suggesting that the closed conformation prevents association with importin alpha.
Assuntos
Proteínas Nucleares/química , Proteínas de Saccharomyces cerevisiae/química , Transporte Ativo do Núcleo Celular/fisiologia , Sequência de Aminoácidos , Animais , Sítios de Ligação , Cristalografia por Raios X , Humanos , Modelos Moleculares , Dados de Sequência Molecular , Proteínas Nucleares/genética , Proteínas Nucleares/metabolismo , Proteínas de Transporte Nucleocitoplasmático , Ligação Proteica , Estrutura Secundária de Proteína , Estrutura Terciária de Proteína , Proteínas de Saccharomyces cerevisiae/genética , Proteínas de Saccharomyces cerevisiae/metabolismo , Alinhamento de Sequência , alfa Carioferinas/metabolismo , Proteína ran de Ligação ao GTP/metabolismoRESUMO
In metazoa, regulation of the phosphorylation state of UPF1 is crucial for nonsense-mediated mRNA decay (NMD), a process by which aberrant mRNAs containing nonsense mutations are degraded. UPF1 is targeted for dephosphorylation by three related proteins, SMG5, SMG6, and SMG7. We report here the crystal structure of the N-terminal domain of SMG7. The structure reveals that SMG7 contains a 14-3-3-like domain. Residues that bind phosphoserine-containing peptides in 14-3-3 are conserved at the equivalent positions in SMG7. Mutation of these residues impairs UPF1 binding to SMG7 in vitro and UPF1 recruitment to cytoplasmic mRNA decay foci in vivo, suggesting that SMG7 acts as an adaptor in targeting mRNAs associated with phosphorylated UPF1 for degradation. The 14-3-3 site of SMG7 is conserved in SMG5 and SMG6. These data also imply that the homologous human Est1 might have a 14-3-3 function at telomeres, and that phosphorylation events may be important for telomerase regulation.