Project description:Yeast Saccharomyces cerevisiae has been widely used as a model system for studying genome instability. Here, heterozygous S. cerevisiae zygotes were generated to determine the genomic alterations induced by sudden introduction of active RNase H2. In combination of a custom SNP microarray, the patterns of chromosomal instability could be explored at a whole genome level. Ribonucleotides can be incorporated into DNA during replication by the replicative DNA polymerases. These aberrant DNA subunits are efficiently recognized and removed by Ribonucleotide Excision Repair, which is initiated by the heterotrimeric enzyme RNase H2. While RNase H2 is essential in higher eukaryotes, the yeast Saccharomyces cerevisiae can survive without RNase H2 enzyme, although the genome undergoes mutation, recombination and other genome instability events at an increased rate. Although RNase H2 can be considered as a protector of the genome from the deleterious events that can ensue from recognition and removal of embedded ribonucleotides, under conditions of high ribonucleotide incorporation and retention in the genome in a RNase H2-negative strain, sudden introduction of active RNase H2 causes massive DNA breaks and genome instability in a condition which we term “ribodysgenesis”. The DNA breaks and genome instability arise solely from RNase H2 cleavage directed to the ribonucleotide-containing genome. Survivors of ribodysgenesis have massive loss of heterozygosity events stemming from recombinogenic lesions on the ribonucleotide-containing DNA, with increases of over 1000X from wild-type. DNA breaks are produced over one to two divisions and subsequently cells adapt to RNase H2 and ribonucleotides in the genome and grow with normal levels of genome instability.
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: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