Project description:Nucleotides on RNA are chemically modified during biogenesis of various mammalian RNA species and RNA modifications have profound effects on RNA function. The 2,2,7-trimethylguanosine modification of the 5′ of RNA molecules is one of the earliest discovered modified nucleotides on mammalian RNAs. Although the TMG cap is one of the most intensively studied RNA modifications, its distribution on a global scale has not been explored. In this study, the locations of the TMG cap on human RNA is determined, using RNA immunoprecipitation coupled with high-throughput sequencing. Although all prototypical modification sites were supported by this study, modification positions of some RNAs were erroneously annotated. In contrast to prototypic sites, many sites reported later were not validated at all. In addition to annotated modification sites, novel candidate sites were found on small Cajal body-specific RNAs.
Project description:Nuclear mRNA processing occurs in a stepwise manner to generate the protein blueprints required for cellular function. The addition of the methyl-7-guanosine (m7G) cap on the 5’end of mRNAs is conserved in humans, plants and fungi. The m7G cap recruits the nuclear cap-binding protein NCBP2 co-/peri-transcriptionally where it mediates interactions between capped-RNAs and the processing machinery. Convention posits that NCBP2 is the sole cap-binding protein in the nucleus positioning cap-chaperoning as an important constitutive, housekeeping function. However, the eukaryotic translation initiation factor eIF4E is also found in the nucleus across Kingdoms. Both eIF4E and NCBP2 employ highly similar structural strategies to directly bind the m7G cap. The presence of two cap-binding factors in the nucleus could arise to provide redundancy to ensure gene expression security or it could provide the basis for tandem regulation of selected subsets of capped-mRNAs driving distinct gene expression programmes. To dissect these possibilities, we compared the spatial localizations, interactomes and impacts on gene expression of eIF4E and NCBP2. We found that like NCBP2, eIF4E physically and spatially associated with active sites of transcription and splicing machinery. However, contrary to expectations, eIF4E and NCBP2 drove distinct transcription and splicing signatures impacting ~1000 transcripts which in turn elicit different biological programmes. RNAs segregated with specific cap-binding proteins with only an overlap of only ~130 transcripts between eIF4E and NCBP2. Clearly, the cap-interaction was not sufficient to elicit sensitivity to these cap-binding proteins given the absence of generalized impacts on the transcriptome. We uncovered the molecular mechanism for cap-chaperone selectivity which lay in differences in conserved sequences motifs within introns of selected mRNAs, their mainly distinct spatial localizations, and differences in the capacity to alter splice factor production. Relevant to the 130 common targets, a fraction of eIF4E and NCBP2 did interact and spatially overlap. Despite their common m7G cap-binding activity, eIF4E and NCBP2 elicit substantively different impacts on gene expression. In contrast to the conventional paradigm, our data support a model whereby cap-chaperones direct processing of distinct subsets of mRNAs thereby eliciting diverse biological programmes. Differential programming by cap-chaperones reveals an unexpected regulatory point in gene expression..
Project description:A series of trinucleotide cap analogs functionalized with an amine-terminated linker at the guanosine ribose and immobilized on BrCN-activated Sepharose was prepared. These affinity resins AR-1 (Am), AR-2 (m6Am), and AR-3 (Bn6Am) were incubated with HEK293F cell extract in the presence of GTP to limit non-specific interactions. The pulled-down proteins were eluted with the corresponding trinucleotide cap analog (m7GpppAmpG for AR-1, m7Gpppm6AmpG for AR-2, and m7GpppBn6AmpG for AR-3), digested with trypsin, labeled with isobaric tags (TMT), and analyzed by shotgun proteomics. This experiment was performed in order to assess binding preferences of proteins to the resins AR-1, AR-2, and AR-3.
Project description:Nuclear mRNA processing occurs in a stepwise manner to generate the protein blueprints required for cellular function. The addition of the methyl-7-guanosine (m7G) cap on the 5’end of mRNAs is conserved in humans, plants and fungi. The m7G cap recruits the nuclear cap-binding protein NCBP2 co-/peri-transcriptionally where it mediates interactions between capped-RNAs and the processing machinery. Convention posits that NCBP2 is the sole cap-binding protein in the nucleus positioning cap-chaperoning as an important constitutive, housekeeping function. However, the eukaryotic translation initiation factor eIF4E is also found in the nucleus across Kingdoms. Both eIF4E and NCBP2 employ highly similar structural strategies to directly bind the m7G cap. The presence of two cap-binding factors in the nucleus could arise to provide redundancy to ensure gene expression security or it could provide the basis for tandem regulation of selected subsets of capped-mRNAs driving distinct gene expression programmes. To dissect these possibilities, we compared the spatial localizations, interactomes and impacts on gene expression of eIF4E and NCBP2. We found that like NCBP2, eIF4E physically and spatially associated with active sites of transcription and splicing machinery. However, contrary to expectations, eIF4E and NCBP2 drove distinct transcription and splicing signatures impacting ~1000 transcripts which in turn elicit different biological programmes. RNAs segregated with specific cap-binding proteins with only an overlap of only ~130 transcripts between eIF4E and NCBP2. Clearly, the cap-interaction was not sufficient to elicit sensitivity to these cap-binding proteins given the absence of generalized impacts on the transcriptome. We uncovered the molecular mechanism for cap-chaperone selectivity which lay in differences in conserved sequences motifs within introns of selected mRNAs, their mainly distinct spatial localizations, and differences in the capacity to alter splice factor production. Relevant to the 130 common targets, a fraction of eIF4E and NCBP2 did interact and spatially overlap. Despite their common m7G cap-binding activity, eIF4E and NCBP2 elicit substantively different impacts on gene expression. In contrast to the conventional paradigm, our data support a model whereby cap-chaperones direct processing of distinct subsets of mRNAs thereby eliciting diverse biological programmes. Differential programming by cap-chaperones reveals an unexpected regulatory point in gene expression..
Project description:We find guanosine supplementation can induce metabolic stress on cells. To evaluate this effect we use RKO-NC and RKO-shPNP cells for experiment.
Project description:To annotate estrogen-regulated eRNAs in MCF-7 breast cancer cells, we used precision nuclear run-on and sequencing of capped RNA (PRO-cap) to determine the transcription start sites of eRNAs.