Project description:We show that these R-loop objects impose specific physical constraints on the DNA, as revealed by the presence of stereotypical angles in the surrounding DNA. Biochemical probing and mutagenesis experiments revealed that the formation of R-loop objects at Airn is dictated by the extruded non-template strand, suggesting that R-loops possess intrinsic sequence-driven properties. Consistent with this, we show that R-loops formed at the fission yeast gene sum3 do not form detectable R-loop objects. Our results reveal that R-loops differ by their architectures and that the organization of the non-template strand is a fundamental characteristic of R-loops, which could explain that only a subset of R-loops is associated with replication-dependent DNA breaks.
Project description:Three-stranded R-loop structures have been associated with genomic instability phenotypes. What underlies their wide-ranging effects on genome stability remains poorly understood. Here we combined biochemical and atomic force microscopy approaches with single molecule R-loop footprinting to demonstrate that R-loops formed at the model Airn locus in vitro adopt a defined set of three-dimensional conformations characterized by distinct shapes and volumes, which we call R-loop objects. Interestingly, we show that these R-loop objects impose specific physical constraints on the DNA, as revealed by the presence of stereotypical angles in the surrounding DNA. Biochemical probing and mutagenesis experiments revealed that the formation of R-loop objects at Airn is dictated by the extruded non-template strand, suggesting that R-loops possess intrinsic sequence-driven properties. Consistent with this, we show that R-loops formed at the fission yeast gene sum3 do not form detectable R-loop objects. Our results reveal that R-loops differ by their architectures and that the organization of the non-template strand is a fundamental characteristic of R-loops, which could explain that only a subset of R-loops is associated with replication-dependent DNA breaks.
Project description:Distribution of R-loops on genomic sites was studied for exponentially growing Escherichia coli in different conditions using strand-specific DRIP-Seq with S9.6 antibodies.
Project description:The formation of R-loops is a natural consequence of the transcription process, caused by invasion of the DNA duplex by nascent transcripts. These structures have been considered rare transcriptional by-products with potential harmful effects on genome integrity, due to the fragility of the displaced DNA coding strand. However R-loops may also possess beneficial effects as their widespread formation has been detected over CpG island promoters in human genes. Furthermore we have previously shown that R-loops are particularly enriched over G-rich terminator elements. These facilitate RNA polymerase II (Pol II) pausing prior to efficient termination. Here we reveal an unanticipated link between R-loops and RNA interference (RNAi)-dependent H3K9me2 formation over pause site termination regions of mammalian protein coding genes. We show that R-loops induce antisense transcription over these pause elements which in turn lead to the generation of double-strand RNA (dsRNA) and recruitment of Dicer, Ago1, Ago2, and G9a histone lysine methyltransferase (HKMT). Consequently an H3K9me2 repressive mark is formed and Heterochromatin Protein 1γ (HP1γ) is recruited, that reinforces Pol II pausing prior to efficient transcriptional termination. We predict that R-loops promote a chromatin architecture that defines the termination region for a substantial subset of mammalian genes. PolIIS2ph ChIP-seq and input in untreated condition and treated with BIX and RNaseH1 overexpression in HeLa cells. The 4 samples have been multiplexed, pooled and sequenced on 3 lanes of Illumina HiSeq2000.
Project description:Inspired by the important roles of the special chromatin structure R-loops, here we report a new method, ssDRIP-seq, for genome-wide identification of R-loops, and demonstrate its high efficiency, low bias, and strand-specificity when profiling the R-loops in Arabidopsis. Using this single-strand DNA ligation based library construction technique, we find that Arabidopsis R-loops are formed in both the sense and antisense orientations of genes, and prefer both AT and GC skews. R-loops are prevalent in regions with multiple chromatin modifications, and are negatively correlated with CG DNA hypermethylation. R-loops are strongly enriched in gene promoters and gene bodies, highly associated with noncoding RNA and repetitive genomic regions, and correlated with activated and repressed gene loci. In summary, our analysis reveals that R-loop is a common feature of the Arabidopsis genome, and suggests diverse roles for R-loops in genome organization and gene regulation, thereby providing novel insights into plant nuclear genome formation and function.
Project description:In plants, the biogenesis of 24 nt and 23 nt small interfering RNAs (siRNAs) requires NUCLEAR RNA POLYMERASE IV (Pol IV), RNA-DEPENDENT RNA POLYMERASE 2 (RDR2) and DICER-LIKE 3 (DCL3). We show that single-stranded M13 bacteriophage DNA can be used as a template for siRNA synthesis in vitro. Deep sequencing of RNAs produced from the in vitro reactions of Pol IV, RDR2 and DCL3 shows that Pol IV transcribes the DNA into first-strand RNAs which RDR2 then uses as templates to synthesize complementary second strands. These siRNA precursor transcripts made by Pol IV and RDR2 are mostly 30-50 nt. An untemplated 3' terminal nucleotide is a characteristic of RDR2 transcripts. DCL3 dicing of double-stranded precursor RNAs synthesized by Pol IV and RDR2 generates siRNAs that are mostly 24 nt, with a smaller population of 23 nt also produced.
Project description:Transcription can pose a threat to genomic stability through the formation of R-loops that obstruct the progression of replication forks. R-loops are three-stranded nucleic acid structures formed by an RNA-DNA hybrid with a displaced non-template DNA strand. We developed RDProx to identify proteins that regulate R-loops in human cells. RDProx relies on the expression of the hybrid-binding domain (HBD) of Ribonuclease H1 (RNaseH1) fused to the ascorbate peroxidase (APEX2), which permits mapping of the R-loop proximal proteome using quantitative mass spectrometry. We associated R-loop regulation with different cellular proteins and identified a role of the tumor suppressor DEAD box protein 41 (DDX41) in opposing R-loop-dependent genomic instability. Depletion of DDX41 resulted in replication stress, double strand breaks and increased inflammatory signaling. Furthermore, DDX41 opposes accumulation of R-loops at gene promoters and its loss leads to upregulated expression of TGFβ and NOTCH signaling genes. Germline loss-of-function mutations in DDX41 lead to predisposition to acute myeloid leukemia (AML) in adulthood. We propose that accumulation of co-transcriptional R-loops, associated gene expression changes and inflammatory response contribute to the development of familial AML with mutated DDX41.