Project description:Eukaryotic cells have to prevent the export of unspliced pre-mRNAs until intron removal is completed to avoid the expression of aberrant and potentially harmful proteins. Only mature RNAs associate with the export receptor Mex67 (mammalian TAP) and enter the cytoplasm. The underlying nuclear quality control mechanisms are still unclear. Here we show that two shuttling SR-proteins Gbp2 and Hrb1 are key surveillance factors for the selective export of spliced mRNAs in yeast. Their absence leads to the significant leakage of unspliced pre-mRNAs into the cytoplasm. They bind to pre-mRNAs and the spliceosome during splicing, where they are necessary for the surveillance of splicing and the stable binding of the TRAMP-complex to the spliceosome-bound transcripts. Faulty transcripts are marked for their degradation at the nuclear exosome. On correct mRNAs the SR-proteins recruit Mex67 upon completion of splicing to allow a quality controlled nuclear export. Altogether, these data identify a role for shuttling SR-proteins in mRNA surveillance and nuclear mRNA quality control. 6 samples, i.e. 2 replicates per protein Gbp2, Hrb1 and Npl3
Project description:Eukaryotic cells have to prevent the export of unspliced pre-mRNAs until intron removal is completed to avoid the expression of aberrant and potentially harmful proteins. Only mature RNAs associate with the export receptor Mex67 (mammalian TAP) and enter the cytoplasm. The underlying nuclear quality control mechanisms are still unclear. Here we show that two shuttling SR-proteins Gbp2 and Hrb1 are key surveillance factors for the selective export of spliced mRNAs in yeast. Their absence leads to the significant leakage of unspliced pre-mRNAs into the cytoplasm. They bind to pre-mRNAs and the spliceosome during splicing, where they are necessary for the surveillance of splicing and the stable binding of the TRAMP-complex to the spliceosome-bound transcripts. Faulty transcripts are marked for their degradation at the nuclear exosome. On correct mRNAs the SR-proteins recruit Mex67 upon completion of splicing to allow a quality controlled nuclear export. Altogether, these data identify a role for shuttling SR-proteins in mRNA surveillance and nuclear mRNA quality control.
Project description:Three shuttling SR-like proteins exist in Saccharomyces cerevisiae, Npl3, Gbp2 and Hrb1, that are involved in the nuclear export of mRNAs. In a screen for genes that regulate the export of Gbp2, we identified novel mutants of the splicing factors PRP8 and PRP17 that lead to severe mislocalization defects for Gbp2 and Hrb1, but not Npl3. Microarray and qRT-PCR analyses show that Gbp2 and Hrb1 preferentially bind to transcripts derived from intron-containing genes. Moreover, in contrast to Npl3, Gbp2 and Hrb1 show genetic and physical interactions with late splicing factors such as Prp17 and Prp43. Further, RNA co-immunoprecipitation experiments reveal that, unlike Npl3, association of Gbp2 and Hrb1 with the mRNA requires splicing, and this in turn is required for their Mex67 recruitment. We propose a model in which Gbp2 and Hrb1 are attached to the mRNAs at late stages of splicing to promote the subsequent export of spliced mRNAs. keyword: RIP-chip RNA-IP of endogenously expressed 3-fold C-terminal myc-tagged Gbp2 and Hrb1 in S288C background cells was each performed once in cells grown to a density of 4x10^7 cells/ml and hybridized against a total (input) RNA reference.
Project description:Mammalian SR proteins are a family of reversibly phosphorylated RNA binding proteins primarily studied for their roles in alternative splicing. While budding yeast lack alternative splicing, they do have three SR-like proteins: Npl3, Gbp2, and Hrb1. However, these have been primarily studied for their roles in mRNA export, leaving their potential roles in splicing largely unexplored. Here we combined high-density genetic interaction profiling and genome-wide splicing-sensitive microarray analysis to demonstrate that a single SR-like protein, Npl3, is required for efficient splicing of a large set of pre-mRNAs in Saccharomyces cerevisiae. We tested the hypothesis that Npl3 promotes splicing by facilitating co-transcriptional recruitment of splicing factors. Using chromatin immunoprecipitation, we showed that mutation of NPL3 reduces the occupancy of U1 and U2 snRNPs at Npl3-stimulated genes. This provides the first evidence that an SR protein can promote recruitment of splicing factors to chromatin.
Project description:Spliced messages constitute one-fourth of expressed mRNAs in the yeast Saccharomyces cerevisiae, and most mRNAs in metazoans. Splicing requires 5' splice site (5'SS), branch point (BP), and 3' splice site (3'SS) elements, but the role of the BP in splicing control is poorly understood because BP identification remains difficult. We developed a high-throughput method, Branch-seq, to map BP and 5'SS of isolated RNA lariats. Applied to S. cerevisiae, Branch-seq detected 76% of expressed, annotated BPs and identified a comparable number of novel BPs. We used RNA-seq to confirm associated 3'SS locations, identifying some 200 novel splice junctions, including an AT-AC intron. We show that several yeast introns use two or even three different BPs, with effects on 3'SS choice, protein coding potential, or RNA stability and identify novel introns whose splicing changes during meiosis or in response to stress. Together, these findings reveal BP-based regulation and demonstrate unanticipated complexity of splicing in yeast.
Project description:Mammalian SR proteins are a family of reversibly phosphorylated RNA binding proteins primarily studied for their roles in alternative splicing. While budding yeast lack alternative splicing, they do have three SR-like proteins: Npl3, Gbp2, and Hrb1. However, these have been primarily studied for their roles in mRNA export, leaving their potential roles in splicing largely unexplored. Here we combined high-density genetic interaction profiling and genome-wide splicing-sensitive microarray analysis to demonstrate that a single SR-like protein, Npl3, is required for efficient splicing of a large set of pre-mRNAs in Saccharomyces cerevisiae. We tested the hypothesis that Npl3 promotes splicing by facilitating co-transcriptional recruitment of splicing factors. Using chromatin immunoprecipitation, we showed that mutation of NPL3 reduces the occupancy of U1 and U2 snRNPs at Npl3-stimulated genes. This provides the first evidence that an SR protein can promote recruitment of splicing factors to chromatin. Splicing-specific microarrays were used to assay changes to splicing in single and double deletion mutants of non-essential SR proteins, in a deletion mutant of a non-essential component of the nonsense-mediated decay pathway, and in a double deletion mutant of in an SR protein plus a non-sense mediated decay factor in Saccharomyces cerevisiae. The data includes both samples obtained at the permissive temperature and also shifts to the non-permissive temperature for some mutants, as well as dye-flipped technical replicates.
Project description:The quality control and export of mRNA by RNA-binding proteins are necessary for the survival of malaria parasites, which have complex life cycles. Malarial nuclear poly(A) binding protein 2 (NAB2), ALWAYS EARLY (ALY) and serine/arginine-rich (SR) proteins, such as nucleolar protein 3 (NPL3), G-strand binding protein 2 (GBP2) and SR1, are involved in nuclear mRNA export in malaria parasites. However, their functions and cellular localization are not fully understood. In this study, we found that NAB2 and SR1, but not ALY, NPL3 or GBP2, played essential roles in the asexual development of malaria parasites, while GBP2 was involved in gametocyte production. Moreover, GBP2 localized to both the nucleus and cytoplasm of malaria parasites and interacted with the proteins ALBA4, DOZI and CITH, which play roles in translational repression. Our findings suggest that malarial GBP2 may be involved in the recruitment of ALBA4, DOZI and CITH. Immunoprecipitation coupled to mass spectrometry (IP-MS) revealed that PHAX domain-containing protein, an adaptor protein for exportin-1, also interacted with GBP2, suggesting that mRNA export occurs via the PHAX domain-containing protein pathway in malaria parasites. Fluorescence live cell imaging revealed that malarial NAB2 localized at the nuclear periphery and co-localized with NUP205. Moreover, using IP-MS, we found that malarial NAB2 interacted with transportin. RNA immunoprecipitation coupled to RNA sequencing revealed that malarial NAB2 bound directly to 143 mRNAs, including those encoding 40S and 60S ribosomal proteins. This indicates that malarial NAB2 is involved in general mRNA assembly and is shuttled between the nucleus and cytoplasm. Our findings suggest that unique mRNA export and post-transcriptional gene regulation mediated by RNA-binding proteins occur in malaria parasites.
Project description:Spliced messages constitute one-fourth of expressed mRNAs in the yeast Saccharomyces cerevisiae, and most mRNAs in metazoans. Splicing requires 5' splice site (5'SS), branch point (BP), and 3' splice site (3'SS) elements, but the role of the BP in splicing control is poorly understood because BP identification remains difficult. We developed a high-throughput method, Branch-seq, to map BP and 5'SS of isolated RNA lariats. Applied to S. cerevisiae, Branch-seq detected 76% of expressed, annotated BPs and identified a comparable number of novel BPs. We used RNA-seq to confirm associated 3'SS locations, identifying some 200 novel splice junctions, including an AT-AC intron. We show that several yeast introns use two or even three different BPs, with effects on 3'SS choice, protein coding potential, or RNA stability and identify novel introns whose splicing changes during meiosis or in response to stress. Together, these findings reveal BP-based regulation and demonstrate unanticipated complexity of splicing in yeast. 1 Lariat-seq experiment library. 3 barcoded Branch-seq libraries that make up one experiment. 26 RNA-seq samples, 2 biological replicates of each.
Project description:We used GFP-tagged SR proteins expressed at endogenous levels and iCLIP to identify and compare endogenous RNA targets of individual SR proteins, map the preferential sites of binding, compare binding pattern and binding motifs between family members and to NXF1 and quantify binding of SR proteins and NXF1 to spliced versus unspliced RNAs to study the role of SR proteins in mRNA export via NXF1.
Project description:Cytoplasmic RNA granules compartmentalize phases of the translation cycle in eukaryotes. We previously reported the localization of oxidized RNA to cytoplasmic foci called oxidized RNA bodies (ORBs) in human cells. We show here that ORBs are RNA granules in Saccharomyces cerevisiae. Several lines of evidence support a role of ORBs in the compartmentalization of no-go decay and ribosome quality control, the translation quality control pathways that recognize and clear aberrant mRNAs, including those with oxidized bases. Translation is required by these pathways and ORBs. Translation quality control factors localize to ORBs. A substrate of translation quality control, a stalled mRNA-ribosome-nascent chain complex, localizes to ORBS. Translation quality control mutants have altered ORB numbers, sizes, or both. In addition, we identify 68 ORB proteins, by immunofluorescence staining directed by proteomics, which further support their role in translation quality control and reveal candidate new factors for these pathways.