Project description:Capture and massively parallel DNA sequencing of ribonucleotides embedded in S. cerevisiae genomic DNA We developed a new method to map the positions of ribonucleotides embedded in DNA using the unique specificity of A. thaliana tRNA ligase. Ribonucleotides were generated in budding yeasts of different genetic backgrounds and mapped to single nucleotide resolution using the new method.
Project description:We report the application of high through-put tag sequencing to measure the location and strand of DNA embedded ribonucleotides in the yeast genome. Mutations in the catalytic subunits of the polymerases (pol1-L868M, pol2-M644G and pol3-L612M) lead to the increased incorporation of ribonucleotides during DNA replication, providing an in vivo label with which to track the contribution of each polymerase to the fully replicated genome. Yeast strains used in this study are deleted for rnh201, encoding the catalytic subunit of the RNase H2 gene so that embedded ribonucleotides are not rapidly removed by ribonucleotide excision repair following DNA replication. Analysis of this data demonstrates that polymerase alpha contributes to the fully replicated genome. Sequencing of DNA embedded ribonucleotides in S. cerevisiae strains to map the contribution of replicative polymerases to the fully replicated genome.
Project description:We report the application of high through-put tag sequencing to measure the location and strand of DNA embedded ribonucleotides in the yeast genome. Mutations in the catalytic subunits of the polymerases (pol1-L868M, pol2-M644G and pol3-L612M) lead to the increased incorporation of ribonucleotides during DNA replication, providing an in vivo label with which to track the contribution of each polymerase to the fully replicated genome. Yeast strains used in this study are deleted for rnh201, encoding the catalytic subunit of the RNase H2 gene so that embedded ribonucleotides are not rapidly removed by ribonucleotide excision repair following DNA replication. Analysis of this data demonstrates that polymerase alpha contributes to the fully replicated genome.
Project description:Whole-genome bisulfite sequencing (WGBS) is currently the gold standard for DNA methylation (5-methylcytosine, 5mC) profiling, however the destructive nature of sodium bisulfite results in DNA fragmentation and subsequent biases in sequencing data. Such issues have led to the development of bisulfite-free methods for 5mC detection. Nanopore sequencing is a long read non-destructive approach that directly analyzes DNA and RNA fragments in real time. Recently, computational tools have been developed that enable base-resolution detection of 5mC from Oxford Nanopore sequencing data. In this chapter we provide a detailed protocol for preparation, sequencing, read assembly and analysis of genome-wide 5mC using Nanopore sequencing technologies.
Project description:Previous work has demonstrated the presence of ribonucleotides in human mitochondrial DNA (mtDNA) and in the present study we use a genome-wide approach to precisely map the location of these. We find that ribonucleotides are distributed evenly between the heavy- and light-strand of mtDNA. The relative levels of incorporated ribonucleotides reflect that DNA polymerase γ discriminates the four ribonucleotides differentially during DNA synthesis. The observed pattern is also dependent on the mitochondrial deoxyribonucleotide (dNTP) pools and disease-causing mutations that change these pools alter both the absolute and relative levels of incorporated ribonucleotides. Our analyses strongly suggest that DNA polymerase γ-dependent incorporation is the main source of ribonucleotides in mtDNA and argues against the existence of a mitochondrial ribonucleotide excision repair pathway in human cells. Furthermore, we clearly demonstrate that when dNTP pools are limiting, ribonucleotides serve as a source of building blocks to maintain DNA replication and genome stability. Increased levels of embedded ribonucleotides in patient cells with disturbed nucleotide pools may constitute to a pathogenic mechanism that affects mtDNA stability and impair new rounds of mtDNA replication
Project description:All DNA polymerases misincorporate ribonucleotides despite their preference for deoxyribonucleotides, and analysis of cultured cells indicates that mammalian mitochondrial DNA (mtDNA) tolerates such replication errors. However, it is not clear to what extent ribonucleotides are incorporated into the mtDNA of solid tissues, or whether they might play a role in human pathologies. Here, we show the DNA in mitochondria of solid tissues contains many more embedded ribonucleotides than that of cultured cells, consistent with the former’s high ratio of ribonucleotide to deoxynucleotide triphosphates and that rAMPs are the predominant ribosubstitution events. This pattern changes in a mouse model of Mpv17 deficiency, as rGMPs are the major embedded ribonucleotides of mtDNA. However, while mitochondrial dGTP is reduced in the liver of the KO mice, the brain shows no change in the overall dGTP pool, leading us to infer that Mpv17 determines the local concentration or quality of dGTP. Embedded rGMPs are expected to impede DNA replication more than other rNMPs, and elevated rGMP incorporation is associated with early-onset mtDNA depletion in liver and late-onset multiple deletions in brain of the Mpv17 ablated mice. These findings suggest that aberrant ribonucleotide incorporation is a primary mtDNA abnormality that can result in pathology.
Project description:5-methylcytosine (5mC) and 5-hydroxymethylcytosine (5hmC) are modified versions of cytosine in DNA with roles in regulating gene expression. Using whole genomic DNA from mouse cerebellum, we have benchmarked 5mC and 5hmC detection by Oxford Nanopore Technologies sequencing against other standard techniques. In addition, we assessed the ability of duplex base-calling to study strand asymmetric modification. Nanopore detection of 5mC and 5hmC is accurate relative to compared techniques and opens new means of studying these modifications. Strand asymmetric modification is widespread across the genome but reduced at imprinting control regions and CTCF binding sites in mouse cerebellum. This study demonstrates the unique ability of nanopore sequencing to improve the resolution and detail of cytosine modification mapping.
Project description:Ribonucleotides incorporated in the genome are a source of endogenous DNA damage, and also serve as signals for repair. Although recent advances of ribonucleotide detection by sequencing, the balance between incorporation and repair of ribonucleotides has not been elucidated. Here, we describe a competitive sequencing method, Ribonucleotide Scanning Quantification sequencing (RiSQ-seq), which enables absolute quantification of misincorporated ribonucleotides throughout the genome by background normalization and standard adjustment within a single sample. RiSQ-seq analysis of cells harboring wild-type DNA polymerases revealed that ribonucleotides were incorporated non-uniformly in the genome with a 3’-shifted distribution and preference for GC sequences. Although ribonucleotide profiles in wild-type and repair-deficient mutant strains showed a similar pattern, direct comparison of distinct ribonucleotide levels in the strains by RiSQ-seq enabled evaluation of ribonucleotide excision repair activity at base resolution and revealed the strand bias of repair. The distinct preferences of ribonucleotide incorporation and repair create vulnerable regions associated with indel hotspots, suggesting that repair at sites of ribonucleotide misincorporation serves to maintain genome integrity and that RiSQ-seq can provide an estimate of indel risk.