Project description:Multiple DNA polymerases are needed to replicate genetic information. Here we describe the use of ribonucleotide incorporation as a biomarker of replication enzymology in vivo. We find that ribonucleotides are incorporated into the yeast nuclear genome in replicase specific and strand-specific patterns that identify replication origins and where polymerase switching occurs. Ribonucleotide density varies across the genome as a function of the replicase, base, local sequence and proximity to nucleosomes and transcription start sites. Ribonucleotides are present in one strand at high densityat mitochondrial replication origins, implying unidirectional replication of a circular genome. The evolutionary conservation of the enzymes that incorporate and process ribonucleotides in DNA suggests that the use of ribonucleotides as biomarkers of DNA synthesis in cells will have widespread applicability. Mapping genomic ribonucleotides in 14 Saccharomyces cerevisiae strains (seven DNA polymerase backgrounds, with or without RNH201), via HydEn-seq (end sequencing of genomic fragments generated by alkaline hydrolysis).
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:Multiple DNA polymerases are needed to replicate genetic information. Here we describe the use of ribonucleotide incorporation as a biomarker of replication enzymology in vivo. We find that ribonucleotides are incorporated into the yeast nuclear genome in replicase specific and strand-specific patterns that identify replication origins and where polymerase switching occurs. Ribonucleotide density varies across the genome as a function of the replicase, base, local sequence and proximity to nucleosomes and transcription start sites. Ribonucleotides are present in one strand at high densityat mitochondrial replication origins, implying unidirectional replication of a circular genome. The evolutionary conservation of the enzymes that incorporate and process ribonucleotides in DNA suggests that the use of ribonucleotides as biomarkers of DNA synthesis in cells will have widespread applicability.
Project description:To investigate nuclear DNA replication enzymology in vivo, we have studied Saccharomyces cerevisiae strains containing a pol2-16 mutation that inactivates the catalytic activities of DNA polymerase δ (Pol δ). Although pol2-16 mutants survive, their spore colonies are very tiny, with increased doubling time, larger than normal cells, aberrant nuclei, and rapid suppressor mutation accumulation. These phenotypes reveal a severe growth defect that is distinct from that of strains that lack Pol δ proofreading (pol2-4), consistent with the idea that Pol δ is the major leading strand replicase. Ribonucleotides are also incorporated into the pol2-16 genome in patterns consistent with leading strand replication by Pol δ when Pol δ is absent. More importantly, ribonucleotide distributions at replication origins suggest that in strains encoding all three replicases, Pol δ contributes to initiation of leading-strand replication. We describe two possible models.
Project description:We have established a novel sequencing approach to characterise usage of replicative DNA polymerases in S. pombe. This approach allows us to determine the roles of DNA polymerase delta and epsilon in lagging strand and leading strand DNA synthesis, respectively in genome-wide scale. Utilising the dataset of usage of these polymerases, we also successfully identified DNA replication initiation sites at high resolution. Furthermore, our informatics analysis establishes genome-wide datasets of fork direction rates, replication timing and the probability of replication termination. We mapped ribonucleotide-incorporation by the mutated DNA polymerase delta and epsilon at single-nucleotide resolution and subsequent informatics analysis was performed to generate datasets listed here.
Project description:We devised and improved on our hydrolytic end sequencing (HydEn-seq) that mapping ribonucleotide incorporation in genome and used this method to track DNA replicative polymerase usage. We uncovered striking exceptions to canonical polymerase division of labor in Saccharomyces cerevisiae and Schizosaccharomyces pombe.