Project description:Pre-mRNA secondary structures are hypothesized to play widespread roles in regulating RNA processing pathways, but these structures have been difficult to visualize in vivo. Here, we characterize S. cerevisiae pre-mRNA structures through transcriptome-wide dimethyl sulfate (DMS) probing, enriching for low-abundance pre-mRNA through splicing inhibition. These data enable evaluation of structures from phylogenetic and mutational studies as well as identification of new structures across 161 introns. We find widespread formation of “zipper stems” between the 5’ splice site and branch point, “downstream stems” between the branch point and the 3’ splice site, and previously uncharacterized long stems that distinguish pre-mRNA from spliced mRNA. Multi-dimensional chemical mapping reveals that intron structures can form in vitro without the presence of binding partners, and structure ensemble prediction suggests that these structures appear in introns across the Saccharomyces genus. We develop the functional assay VARS-seq to characterize variants of RNA structure in high-throughput and we apply the method on 135 sets of stems across 7 introns, finding that some structured elements can increase spliced mRNA levels despite being distal from canonical splice sites. Unexpectedly, other structures including zipper stems can increase retained intron levels. This transcriptome-wide inference of intron RNA structures suggests new ideas and model systems for understanding how pre-mRNA folding influences gene expression.
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: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:Spliceosomal introns are ubiquitous non-coding RNAs typically destined for rapid debranching and degradation. Here, we describe 34 excised Saccharomyces cerevisiae introns that, although rapidly degraded in log-phase growth, accumulate as linear RNAs under either saturated-growth conditions or other stresses that cause prolonged inhibition of TORC1, a key integrator of growth signaling. Introns that become stabilized remain associated with components of the spliceosome and differ from other spliceosomal introns in having a short distance between their lariat branch point and 3´ splice site, which is necessary and sufficient for their stabilization. Deletion of these unusual introns is disadvantageous in saturated conditions and causes aberrantly high growth rates of yeast chronically challenged with the TORC1 inhibitor rapamycin. Reintroduction of native or engineered stable introns suppresses this aberrant rapamycin response. Thus, excised introns function within the TOR growth-signaling network of S. cerevisiae, and more generally, excised spliceosomal introns can have biological functions.
Project description:In parallel to the genetic code for protein synthesis, a second layer of information is embedded in all RNA transcripts in the form of RNA structure. The ability of RNA to base pair with itself and other nucleic acids endow RNA with the capacity to form extensive structures, which are known to influence practically every step in the gene expression program1. Yet the nature of most RNA structures or effects of sequence variation on structure are not known. Here we report the initial landscape and variation of RNA secondary structures (RSS) in a human family trio, providing a comprehensive RSS map of human coding and noncoding RNAs. We identify unique RSS signatures that demarcate open reading frames, splicing junctions, and define authentic microRNA binding sites. Comparison of native deproteinized RNA isolated from cells versus refolded purified RNA suggests that the majority of the RSS information is encoded within RNA sequence. Over one thousand transcribed single nucleotide variants (~15% of all transcribed SNVs) alter local RNA structure; these “RiboSNitches”2 occur in disease-associated variants. We discover simple sequence and spacing rules that determine the ability of point mutations to impact RSS. Selective depletion of RiboSNitches versus structurally synonymous variants at precise locations suggests selection for specific RNA shapes at thousands of sites, including 3’UTRs, binding sites of miRNAs and RNA binding proteins genome-wide. These results highlight the potentially broad contribution of RNA structure and its variation to gene regulation. RNA structure probing is performed at 37˚C on poly(A)+ selected RNAs from GM12878, GM12891 and GM12892 cell lines, as well as on native proteinized RNAs from GM12878. The structure probed RNAs is then cloned into a sequencing library using modied Ambion RNA sequencing kit compatible with the Illumina platform. The samples were deep sequenced using Illumina's Hi-Seq platform. AGO CLIP was performed as reported. Cells were crosslinked with UV and lysed using published protocols. AGO2 was enriched using immunopurification. The RNA-protein complex was digested with ribonuclease and purified by gel electrophoresis. Purified RNA was reverse transcribed and cDNA molecules were amplified and sequenced as described.
Project description:The structures of RNA molecules are often important for their function and regulation, yet there are no experimental techniques for genome-scale measurement of RNA structure. Here, we describe a novel strategy termed Parallel Analysis of RNA Structure (PARS), which is based on deep sequencing fragments of RNAs that were treated with structure-specific enzymes, thus providing simultaneous in-vitro profiling of the secondary structure of thousands of RNA species at single nucleotide resolution. We apply PARS to profile the secondary structure of the mRNAs of the budding yeast S. cerevisiae and obtain structural profiles for over 3000 distinct transcripts. Analysis of these profiles reveals several RNA structural properties of yeast transcripts, including the existence of more secondary structure over coding regions compared to untranslated regions, a three-nucleotide periodicity of secondary structure across coding regions, and a relationship between the efficiency with which an mRNA is translated and the lack of structure over its translation start site. PARS is readily applicable to other organisms and to profiling RNA structure in diverse conditions, thus enabling studies of the dynamics of secondary structure at a genomic scale. RNA sample was treated with one of two structure-specific enzymes (RNase V1 or RNase S1). Four independent V1 experiments and three independent S1 experiments were carried out. Processed data file linked below. Data processing involves merging (or rather log-ratio-ing) the 7 lanes of SOLiD sequencing data against each other. Also linked below are the genome and transcriptome FASTA files used for mapping, and the annotation file having the format: gene_ID, chromosome, start, end, feature. Start and end are 1-based; feature is "Transcript" for the entire transcript (including introns), "Intron", "Exon", "5UTR" or "3UTR". Genome-wide measurement of RNA secondary structure in yeast, Kertesz et al., Nature Volume:467, Pages:103-107, Date published:(02 September 2010) http://www.nature.com/nature/journal/v467/n7311/abs/nature09322.html
Project description:High density yeast tiling array reveals new introns and extensive meiotic splicing regulation. Knowing gene structure is vital to understanding gene function, and accurate genome annotation is essential for understanding cellular function. To this end, we have developed an assay for genome-wide mapping of introns in Saccharomyces cerevisiae. Using high-density tiling arrays we compared wild type yeast to a mutant deficient for intron degradation. Our method identified 76% of the known introns, verified the existence of an additional 18 predicted introns, and revealed six new introns. Furthermore, we discovered that all 13 meiosis-specific intronic yeast genes undergo regulated splicing, which provides post-transcriptional regulation of the genes involved in yeast cell differentiation. Moreover, we found that >10% of intronic genes in yeast are incompletely spliced during exponential growth in rich media, suggesting that meiosis is not the only cellular function regulated by splicing. The method provides a clear snapshot of the spliced transcriptome in yeast. Our tiling array assay can be used to explore a variety of cellular environments and should be readily adaptable to the study of other organisms including humans.
Project description:In parallel to the genetic code for protein synthesis, a second layer of information is embedded in all RNA transcripts in the form of RNA structure. The ability of RNA to base pair with itself and other nucleic acids endow RNA with the capacity to form extensive structures, which are known to influence practically every step in the gene expression program1. Yet the nature of most RNA structures or effects of sequence variation on structure are not known. Here we report the initial landscape and variation of RNA secondary structures (RSS) in a human family trio, providing a comprehensive RSS map of human coding and noncoding RNAs. We identify unique RSS signatures that demarcate open reading frames, splicing junctions, and define authentic microRNA binding sites. Comparison of native deproteinized RNA isolated from cells versus refolded purified RNA suggests that the majority of the RSS information is encoded within RNA sequence. Over one thousand transcribed single nucleotide variants (~15% of all transcribed SNVs) alter local RNA structure; these “RiboSNitches”2 occur in disease-associated variants. We discover simple sequence and spacing rules that determine the ability of point mutations to impact RSS. Selective depletion of RiboSNitches versus structurally synonymous variants at precise locations suggests selection for specific RNA shapes at thousands of sites, including 3’UTRs, binding sites of miRNAs and RNA binding proteins genome-wide. These results highlight the potentially broad contribution of RNA structure and its variation to gene regulation.