Biology subjects

Stirling, P. C.

Publications and source records attributed to Stirling, P. C..

3 recordsLinked to original sources

bioRxiv2018

The yeast core spliceosome maintains genome integrity through R-loop prevention and alpha-tubulin expression

To achieve genome stability cells must coordinate the action of various DNA transactions including DNA replication, repair, transcription and chromosome segregation. How transcription and RNA processing enable genome stability is only partly understood. Two predominant models have emerged: one involving changes in gene expression that perturb other genome maintenance factors, and another in which genotoxic DNA:RNA hybrids, called R-loops, impair DNA replication. Here we characterize genome instability phenotypes in a panel yeast splicing factor mutants and find that mitotic defects, and in some cases R-loop accumulation, are causes of genome instability. Genome instability in splicing mutants is exacerbated by loss of the spindle-assembly checkpoint protein Mad1. Moreover, removal of the intron from the -tubulin gene TUB1 restores genome integrity. Thus, while R-loops contribute in some settings, defects in yeast splicing predominantly lead to genome instability through effects on gene expression.

cell biology↗

bioRxiv2017

Conserved roles of RECQ-like helicases Sgs1 and BLM in preventing R-loop induced genome instability

Sgs1 is a yeast DNA helicase functioning in DNA replication and repair, and is the orthologue of the human Blooms syndrome helicase BLM. Here we analyze the mutation signature associated with SGS1 deletion in yeast, and find frequent copy number changes flanked by regions of repetitive sequence and high R-loop forming potential. We show that loss of SGS1 increases R-loop accumulation and sensitizes cells to replication-transcription collisions. Accordingly, in sgs1{Delta} cells the genome-wide distribution of R-loops shifts to known sites of Sgs1 action, replication pausing regions, and to long genes. Depletion of the orthologous BLM helicase from human cancer cells also increases R-loop levels, and R-loop-associated genome instability. In support of a direct effect, BLM is found physically proximal to DNA:RNA hybrids in human cells, and can efficiently unwind R-loops in vitro. Together our data describe a conserved role for Sgs1/BLM in R-loop suppression and support an increasingly broad view of DNA repair and replication fork stabilizing proteins as modulators of R-loop mediated genome instability.

cell biology↗

bioRxiv2016

Synthetic hypermutation: gene-drug mutation rate synergy reveals a translesion synthesis mechanism

Gene-gene or gene-drug interactions are typically quantified using fitness as readout because the data is continuous and easily measured in high-throughput. However, to what extent fitness captures the range of other phenotypes that show synergistic effects is usually unknown. Using Saccharomyces cerevisiae, and focusing on a matrix of DNA repair mutants and genotoxic drugs, we quantify 76 gene-drug interactions based on both mutation rate and fitness and find that these parameters are not necessarily overlapping. Independent of fitness defects we identified six cases of synthetic hypermutation, where the combined effect of the drug and mutant on mutation rate was greater than predicted. One example occurred when yeast lacking RAD1 were exposed to cisplatin and we characterized this interaction using whole-genome sequencing. Our sequencing results indicate mutagenesis by cisplatin in rad1{Delta} cells appeared to depend almost entirely on interstrand crosslinks at GpCpN motifs. Interestingly, our data suggests that the 3 base in these motifs templates the addition of the mutated base. This result differs from cisplatin mutation signatures in XPF-deficient C. elegans and supports a model in which translesion synthesis polymerases perform a slippage and realignment extension across from the damaged base. Accordingly, DNA polymerase {zeta} activity was essential for mutagenesis in cisplatin treated rad1{Delta} cells. Together these data reveal the potential to gain new mechanistic insights from non-fitness measures of gene-drug interactions and extend the use of mutation accumulation and whole-genome sequencing analysis to define DNA repair mechanisms.

genetics↗