Project description:Protein-coding genes in eukaryotes are transcribed by RNA polymerase II (Pol II) and introns are removed from pre-mRNA by the spliceosome. Understanding the time lag between Pol II progression and splicing could provide mechanistic insights into the regulation of gene expression. Here, we present two single-molecule nascent RNA sequencing methods that directly determine the progress of splicing catalysis as a function of Pol II position. Endogenous genes were analyzed on a global scale in budding yeast. We show that splicing is 50% complete when Pol II is only 45 nt downstream of introns, with the first spliced products observed as introns emerge from Pol II. Perturbations that slow the rate of spliceosome assembly or speed up the rate of transcription caused splicing delays, showing that regulation of both processes determines in vivo splicing profiles. We propose that matched rates streamline the gene expression pathway, while allowing regulation through kinetic competition.
Project description:Targeted paired-end sequencing of cDNA from unfragmented nascent RNA from exponentially growing S. cerevisiae cells was employed to obtain Pol II transcription elongation and splicing information from single transcripts. Nascent RNA was prepared from the yeast chromatin fraction (Carrillo Oesterreich, Preibisch, Neugebauer, Mol Cell 2010) or enriched from total RNA with polyadenylated RNA depletion. The nascent 3â end was labeled with a 3â DNA adaptor through ligation. A PCR with a forward primer in the first exon of select intron-containing genes amplifies nascent transcripts of specific genes and ensures sequencing adaptor attachment for paired-end sequencing. With this approach co-transcriptional splicing progression with distance from the intron end could be analyzed for 87 genes. Note that the unmapped and mapped data also include genes that did not pass the read coverage requirements in SMIT analysis. Nascent RNA profiles for mainly intron-containing genes were generated with paired-end sequencing with Illumina HiSeq technology.
Project description:N6-methyladenosines (m6A) are stoichiometrically deposited on exons of nearly one third of RNA Pol II transcriptome, mainly catalysed by METTL3/14 complex. However, neither the intronic methylation pattern and its functional relevance nor the immediate response upon m6A loss have been fully understood. Here we applied MeRIP-seq on mESC nascent transcriptome and thus revealed that approximately 6-10% of m6A peaks occurred at intronic regions, preferentially the conserved and alternative exon/intron part of longer introns, proximately to 5’-splice sites. These intronic m6A deposition correlates with both Rbm15 binding and H3K36me3. Moreover, coupled 4sU-seq with METTL3 dTAG system in mESC, we found that m6A mediates alternative exon/intron inclusive in nascent transcriptome. Intriguingly, m6A self-regulation including writers and readers are early response and partially contributed by alternative splicing changes. Collectively, our study presents a unified model that m6A mediates alternative splicing, and dTAG METTL3 opens an avenue to interrogate the direct response of functional m6A disruption.
Project description:Long read SMRT cDNA sequencing of nascent RNA from exponentially growing S. cerevisiae and S. pombe cells was employed to obtain transcription elongation and splicing information from single transcripts. Nascent RNA was prepared from the yeast chromatin fraction (Carrillo Oesterreich, Preibisch, Neugebauer, Mol Cell 2010). The nascent 3â?? end was labeled with a 3â?? DNA adaptor through ligation. The adaptor sequence served as template for full-length reverse transcription and double-stranded cDNA was obtained in a PCR (gene-specific or transcriptome-wide). SMRT DNA sequencing libraries were prepared subsequently. Nascent RNA profiles for mainly intron-containing genes were generated with long-read SMRT cDNA sequencing.
Project description:During maturation, eukaryotic precursor RNAs undergo processing events including intron splicing, 3’-end cleavage, and polyadenylation. Here, we describe nanopore analysis of CO-transcriptional Processing (nano-COP), a method for probing the timing and patterns of RNA processing. An extension of native elongating transcript sequencing (NET-seq), which quantifies transcription genome-wide through short-read sequencing of nascent RNA 3’ ends, nano-COP uses long-read nascent RNA sequencing to observe global patterns of RNA processing. First, nascent RNA is stringently purified through a combination of 4-thiouridine metabolic labeling and cellular fractionation. In contrast to cDNA or short-read–based approaches relying on reverse transcription or amplification, the sample is sequenced directly through nanopores to reveal the native context of nascent RNA. nano-COP identifies both active transcription sites and splice isoforms of single RNA molecules during synthesis, providing insight into patterns of intron removal and the physical coupling between transcription and splicing. The nano-COP protocol yields data within 3 days.
Project description:Continuous translation elongation, irrespective of amino acid sequences, is a prerequisite for living organisms to produce their proteomes. However, the risk of elongation abortion is concealed within nascent polypeptide products. For example, negatively charged sequences with occasional intermittent prolines, termed intrinsic ribosome destabilization (IRD) sequences, destabilizes the translating ribosomal complex. Thus, some nascent chain sequences lead to premature translation cessation. Here, we show that most potential IRD sequences in the middle of open reading frames remain cryptic by two mechanisms: the nascent polypeptide itself that spans the exit tunnel and its bulky amino acid residues that occupy the tunnel entrance region. Thus, nascent polypeptide products have a built-in ability to ensure elongation continuity by serving as a bridge and thus by protecting the large and small ribosomal subunits from dissociation.
Project description:Targeted paired-end sequencing of cDNA from unfragmented nascent RNA from exponentially growing S. cerevisiae cells was employed to obtain Pol II transcription elongation and splicing information from single transcripts. Nascent RNA was prepared from the yeast chromatin fraction (Carrillo Oesterreich, Preibisch, Neugebauer, Mol Cell 2010) or enriched from total RNA with polyadenylated RNA depletion. The nascent 3’ end was labeled with a 3’ DNA adaptor through ligation. A PCR with a forward primer in the first exon of select intron-containing genes amplifies nascent transcripts of specific genes and ensures sequencing adaptor attachment for paired-end sequencing. With this approach co-transcriptional splicing progression with distance from the intron end could be analyzed for 87 genes. Note that the unmapped and mapped data also include genes that did not pass the read coverage requirements in SMIT analysis.
Project description:RNA sequences are expected to be identical to their corresponding DNA sequences. Advances in technologies have enabled deep sequencing of nucleic acids that uncovered exceptions to the one-to-one relationship between DNA and RNA sequences. Previously in human cells, post-transcriptional RNA editing was the only known mechanism that changes RNA sequences from the underlying DNA sequences. Here, we sequenced nascent RNA and found all 12 types of RNA-DNA differences. Using various experimental analyses, we validated this finding. Our results showed that sequences of nascent RNAs within 40 nucleotides of the exit channel of RNA polymerase II already differ from the corresponding DNA sequences. These RNA-DNA differences are mediated by RNA processing steps closely coupled with transcription and not by known deaminase-mediated RNA editing mechanisms nor during NTP incorporation by Pol II. This finding identifies sequence substitution as part of co-transcriptional RNA processing. We sequenced nascent RNA using global run-on sequencing, GRO-seq from human B-cells from two individuals and a variant of the GRO-seq procedure, known as precision run-on sequencing, PRO-seq. The RNAs are prepared after a short run-on assay performed with isolated nuclei in the presence of Br-UTP. The isolated RNAs are base hydrolyzed to ~100 nucleotides and affinity purified with anti-BrU beads three times at each successive step of preparing the RNAs for orientation-specific sequencing using Illumina technology. The 5M-bM-^@M-^Y ~half of each sequence represents nascent RNA made in the cell and the 3M-bM-^@M-^Y ~half represents sequences made in vitro during the run-on reaction. The precision variation, PRO-seq, incorporates one or at most a few biotin-labeled nucleoside triphosphates during the run-on, and sequencing from the 3M-bM-^@M-^Y end of this affinity purified, nascent RNA maps the cellular location of engaged polymerases with near single nucleotide precision. We obtained ~ 100 million 100-nucleotide uniquely mapped GRO-seq reads from B-cells of two individuals. For one subject, we also carried out pGRO-seq and obtained 60 million uniquely mapped reads. In addition, we sequenced ~135 million uniquely mapped RNA-seq reads, and the corresponding DNA of the two individuals to 30X and 60X coverage. Additionally, we isolated and sequenced nascent RNA with an alternate method described by Wuarin and Schibler (1994) in order to compare chromatin-bound RNA to the very nascent RNA from PRO-seq. We obtained ~190 million uniquely mapped reads from chormatin-bound RNA-seq.