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: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 conserved SR-like protein Npl3 promotes the splicing of diverse pre-mRNAs. However, the RNA sequence(s) recognized by the RNA Recognition Motifs (RRM1 & RRM2) of Npl3 during the splicing reaction remain elusive. Here, we developed a split-iCRAC approach in vivo to determine the consensus sequence bound to each RRM in yeast. High-resolution NMR structures show that RRM2 recognizes a 5´-GNGG-3´ motif leading to an unusual mille-feuille topology. In addition, our data indicate a non-specific interaction of the RS domain with RNA. These structures reveal how RRM1 preferentially interacts with a CC-dinucleotide upstream of this motif, and how the inter-RRM linker and the region C-terminal to RRM2 contributes to cooperative RNA-binding. Structure-guided studies show that Npl3 genetically interacts with U2 snRNP specific factors and we provide evidence that Npl3 melts U2 snRNA stem-loop I, a prerequisite for U2/U6 duplex formation within the catalytic centre of the Bact spliceosomal complex. Our findings provide a mechanistic role for Npl3 during spliceosome active site formation.
Project description:Yeast Npl3 is a highly abundant RNA binding protein, related to metazoan SR proteins, with reported functions including transcription elongation, splicing and RNA 3’ end processing. To identify direct targets and functions for Npl3, we used UV crosslinking and analysis of cDNA (CRAC) to map precise RNA binding sites. Npl3 binds diverse RNA species, at sites indicative of roles in both early pre-mRNA processing and 3’ end formation on mRNAs and ncRNAs. Consistent with this, tiling array and RNAPII binding data revealed 3’ extended mRNA and snoRNA transcripts in the absence of Npl3. This reflected transcriptional readthrough by RNAPII, and extension and stabilization of cryptic unstable transcript (CUT) long noncoding RNAs. Transcription readthrough was widespread, often resulting in down-regulation of neighboring genes. We conclude that Npl3 is required for the formation of a termination-competent RNA, affecting both coding and noncoding RNAs.
Project description:Yeast Npl3 is a highly abundant RNA binding protein, related to metazoan SR proteins, with reported functions including transcription elongation, splicing and RNA 3’ end processing. To identify direct targets and functions for Npl3, we used UV crosslinking and analysis of cDNA (CRAC) to map precise RNA binding sites. Npl3 binds diverse RNA species, at sites indicative of roles in both early pre-mRNA processing and 3’ end formation on mRNAs and ncRNAs. Consistent with this, tiling array and RNAPII binding data revealed 3’ extended mRNA and snoRNA transcripts in the absence of Npl3. This reflected transcriptional readthrough by RNAPII, and extension and stabilization of cryptic unstable transcript (CUT) long noncoding RNAs. Transcription readthrough was widespread, often resulting in down-regulation of neighboring genes. We conclude that Npl3 is required for the formation of a termination-competent RNA, affecting both coding and noncoding RNAs.
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:Splicing regulatory networks are essential components of eukaryotic gene expression programs, yet little is known about how they are integrated with transcriptional regulatory networks into coherent gene expression programs. Here we define the MER1 splicing regulatory network and examine its role in the gene expression program during meiosis in budding yeast. Mer1p splicing factor promotes splicing of just four pre-mRNAs. All four Mer1p-responsive genes also require Nam8p for splicing activation by Mer1p, however other genes require Nam8p but not Mer1p, exposing an overlapping meiotic splicing network controlled by Nam8p. MER1 mRNA and three of the four Mer1p substrate pre-mRNAs are induced by the transcriptional regulator Ume6p. This unusual arrangement delays expression of Mer1p-responsive genes relative to other genes under Ume6p control. Products of Mer1p-responsive genes are required for initiating and completing recombination, and for activation of Ndt80p, the transcriptional network that controls subsequent steps in the program. Thus the MER1 splicing regulatory network mediates the dependent relationship between the UME6 and NDT80 transcriptional regulatory networks in the meiotic gene expression program. This work reveals how splicing regulatory networks can be interlaced with transcriptional regulatory networks in eukaryotic gene expression programs. This SuperSeries is composed of the SubSeries listed below.