TRNA pool analysis of S. cerevisiae using tRNA-HySeq
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ABSTRACT: For a typical RNA polymerase (pol) II transcribed budding yeast gene, the 5' -end is characterized by a nucleosome-free region (NFR) immediate upstream of the transcription start site (TSS), flanked by two well-positioned nucleosomes (-1 and +1) containing H2A.Z. A similar arrangement of nucleosomes containing H2A.Z is found on the genes transcribed by pol III, which reside in the NFR actively maintained by the chromatin remodeling complexes. We did genome-wide MNase-seq and ChIP-seq experiments to study the nucleosome arrangement near pol III transcribed genes. We also measured the levels of different tRNAs in the tRNA pool of the wild type and Spt16 mutant (*spt16-197*) cells using tRNA-HySeq method. Although, it is difficult to measure the primary transcripts of tRNA due to their quick processing and the sequence degeneracy of the tRNA isogenes; a comparison of the wild type and Spt16 mutant showed both increase or decrease of tRNA transcripts. The result suggest that Spt16 may not be necessary for the transcription per se of tRNA genes.
Project description:In S. cerevisiae, histone variant H2A.Z is deposited in euchromatin at the flanks of silent heterochromatin to prevent its ectopic spread. The degree to which H2A.Z is found and functions elsewhere is unknown. Here we show that H2A.Z nucleosomes are found at promoter regions of nearly all genes in euchromatin. They generally occur as two positioned nucleosomes that flank a nucleosome-free region (NFR) that contains the transcription start site. Astonishingly, enrichment at 5’ ends is independent of transcriptional state as it is observed not only at actively transcribed genes, but also at inactive loci. Mutagenesis of a typical promoter revealed a 22 bp segment of DNA sufficient to program formation of a NFR flanked by two H2A.Z nucleosomes. This segment contains a binding site of the Myb-related protein Reb1 and an adjacent dT:dA tract. Efficient deposition of H2A.Z is further promoted by a specific pattern of histone H3 and H4 tail acetylation and the bromodomain protein Bdf1, a component of the Swr1 complex that deposits H2A.Z. These data define DNA- and histone-based mechanisms by which dividing cells define the 5’ ends of genes and preserve their euchromatic state in the absence of transcription. Keywords: ChIP-chip
Project description:During transcription the nascent RNA can invade the DNA template, forming extended RNA-DNA duplexes (R-loops). Here we employ ChIP-seq in strains expressing or lacking RNase H to map targets of RNase H activity throughout budding yeast genome. In wild-type strains, R-loops were readily detected over the 35S rDNA region transcribed by Pol I and over the 5S rDNA transcribed by Pol III. In strains lacking RNase H activity, R-loops were elevated over other Pol III genes notably tRNAs, SCR1 and U6 snRNA, and were also associated with the cDNAs of endogenous TY1 retrotransposons, which showed increased rates of mobility to the 5?-flanking regions of tRNA genes. Unexpectedly, R-loops were also associated with mitochondrial genes in the absence of RNase H1, but not of RNase H2. Finally, R-loops were detected on highly expressed protein-coding genes in the wild-type, notably over the second exon of spliced ribosomal protein genes. ChIP-seq of RNA-DNA hybrids using antibody S9.6
Project description:To further our understanding of the RNAi machinery within the human nucleus, we analyzed the chromatin and RNA binding of Argonaute 2 (AGO2) within human cancer cell lines. Our data indicated that AGO2 binds directly to nascent tRNA and 5S rRNA, and to the genomic loci from which these RNAs are transcribed, in a small RNA- and DICER-independent manner. AGO2 chromatin binding was not observed at non-TFIIIC-dependent RNA polymerase (Pol) III genes or at extra-TFIIIC (ETC) sites, indicating that the interaction is specific for TFIIIC-dependent Pol III genes. A genome-wide analysis indicated that loss of AGO2 caused a global increase in the mRNA expression level among genes that flank AGO2-bound tRNA genes. This effect was shown to be distinct from that of the disruption of DICER, DROSHA, or CTCF. We propose that AGO2 binding to tRNA genes has a novel and important regulatory role in human cells. ChIP-seq for AGO2 was performed from K562 cells using 2 commercially available monoclonal antibodies (mAbs) and 5 replicates. Replicates 1-3 were performed with Millipore 04-642, and replicates 4 and 5 were performed with Abcam 57113. RNA-seq was carried out on 2 replicates of shMock and 2 replicates of shAGO2. Lentiviral vectors GIPZ Lentiviral #RHS4531-EG271611.
Project description:To further our understanding of the RNAi machinery within the human nucleus, we analyzed the chromatin and RNA binding of Argonaute 2 (AGO2) within human cancer cell lines. Our data indicated that AGO2 binds directly to nascent tRNA and 5S rRNA, and to the genomic loci from which these RNAs are transcribed, in a small RNA- and DICER-independent manner. AGO2 chromatin binding was not observed at non-TFIIIC-dependent RNA polymerase (Pol) III genes or at extra-TFIIIC (ETC) sites, indicating that the interaction is specific for TFIIIC-dependent Pol III genes. A genome-wide analysis indicated that loss of AGO2 caused a global increase in the mRNA expression level among genes that flank AGO2-bound tRNA genes. This effect was shown to be distinct from that of the disruption of DICER, DROSHA, or CTCF. We propose that AGO2 binding to tRNA genes has a novel and important regulatory role in human cells.
Project description:Pathogenic variants in subunits of RNA polymerase (Pol) III cause a spectrum of neurodegenerative diseases including 4H leukodystrophy. We developed a postnatal whole-body mouse model expressing pathogenic mutations in Polr3a to examine the molecular mechanisms by which reduced Pol III activity results primarily in central nervous system phenotypes. Polr3a mutant mice exhibit behavioral deficits, exocrine pancreatic atrophy and cerebral pathology. Transcriptome and immunohistochemistry analyses of cerebra show a reduction in most Pol III transcripts, induction of innate immune and integrated stress responses and cell type-specific gene expression changes reflecting neuron and oligodendrocyte loss and microglial activation. A global decrease in mature tRNA levels and an altered tRNA profile preceded cerebral neurodegeneration suggesting a causal role in disease initiation. In cerebella, heart and kidney, Pol III transcripts other than tRNAs were generally unaffected. The results suggest tissue-specific thresholds of sensitivity to defects in Pol III transcription.
Project description:Increasing evidence suggests that tRNA levels are dynamically and specifically regulated in response to internal and external cues to modulate the cellular translational program. However, the molecular players and the mechanisms regulating the gene-specific expression of tRNAs are still unknown. Using an inducible auxin-degron system to rapidly deplete RPB1 (the largest subunit of RNA Pol II) in living cells, we identified Pol II as a direct gene-specific regulator of tRNA transcription. Our data suggest that Pol II transcription robustly interferes with Pol III function at specific tRNA genes. This activity was further found to be essential for MAF1-mediated repression of a large set of tRNA genes during serum starvation, indicating that repression of tRNA genes by Pol II is dynamically regulated. Hence, Pol II plays a direct and central role in the gene-specific regulation of tRNA expression.
Project description:Transfer RNAs are required for translating genetic information into protein sequence. The human genome contains hundreds of tRNA genes, many of which in multiple copies. How their expression is regulated to control functional tRNA levels is unknown. Here, we combined quantitative tRNA profiling and ChIP-Seq to measure tRNA expression upon differentiation of human induced pluripotent stem cells (hiPSC) into neuronal and cardiac cells. We find that tRNA transcript pools vary substantially, while the abundance of tRNAs with distinct anticodons, which governs decoding rates, is more stable among cell types. Mechanistically, RNA Polymerase III (Pol III) samples a wide range of tRNA genes in hiPSC and becomes constrained to a housekeeping subset upon differentiation. This is mediated by diminished mTOR signaling, which activates the Pol III repressor MAF1. Our data rationalize how tRNA anticodon pools are buffered in different cellular contexts and reveal that mTOR activity drives selective tRNA expression.
Project description:Increasing evidence suggests that tRNA levels are dynamically and specifically regulated in response to internal and external cues to modulate the cellular translational program. However, the molecular players and the mechanisms regulating the gene-specific expression of tRNAs are still unknown. Using an inducible auxin-degron system to rapidly deplete RPB1 (the largest subunit of RNA Pol II) in living cells, we identified Pol II as a direct gene-specific regulator of tRNA transcription. Our data suggest that Pol II transcription robustly interferes with Pol III function at specific tRNA genes. This activity was further found to be essential for MAF1-mediated repression of a large set of tRNA genes during serum starvation, indicating that repression of tRNA genes by Pol II is dynamically regulated. Hence, Pol II plays a direct and central role in the gene-specific regulation of tRNA expression.
Project description:During transcription the nascent RNA can invade the DNA template, forming extended RNA-DNA duplexes (R-loops). Here we employ ChIP-seq in strains expressing or lacking RNase H to map targets of RNase H activity throughout budding yeast genome. In wild-type strains, R-loops were readily detected over the 35S rDNA region transcribed by Pol I and over the 5S rDNA transcribed by Pol III. In strains lacking RNase H activity, R-loops were elevated over other Pol III genes notably tRNAs, SCR1 and U6 snRNA, and were also associated with the cDNAs of endogenous TY1 retrotransposons, which showed increased rates of mobility to the 5?-flanking regions of tRNA genes. Unexpectedly, R-loops were also associated with mitochondrial genes in the absence of RNase H1, but not of RNase H2. Finally, R-loops were detected on highly expressed protein-coding genes in the wild-type, notably over the second exon of spliced ribosomal protein genes.
Project description:Increasing evidence suggests that tRNA levels are dynamically and specifically regulated in response to internal and external cues to modulate the cellular translational program. However, the molecular players and the mechanisms regulating the gene-specific expression of tRNAs are still unknown. Using an inducible auxin-degron system to rapidly deplete RPB1 (the largest subunit of RNA Pol II) in living cells, we identified Pol II as a direct gene-specific regulator of tRNA transcription. Our data suggest that Pol II transcription robustly interferes with Pol III function at specific tRNA genes. This activity was further found to be essential for MAF1-mediated repression of a large set of tRNA genes during serum starvation, indicating that repression of tRNA genes by Pol II is dynamically regulated. Hence, Pol II plays a direct and central role in the gene-specific regulation of tRNA expression.