Faithful transmission of the genome requires the concerted functions of DNA replication, checkpoint surveillance, and DNA repair pathways in order to prevent the chromosome rearrangements, aneuploidy, and accumulation of mutations that are hallmarks of cancerous cells.

We have a long-standing interest in the molecular mechanisms by which DNA replication is regulated in eukaryotic cells. More recently we have become interested in the broader mechanisms that protect the integrity of the genome from damage that arises both from exogenous agents (chemical, radiation) and from cellular processes, particularly DNA replication itself.

Our studies use the budding yeast Saccharomyces cerevisiae and the fission yeast Schizosaccharomyces pombe as models. Homologues of many of the replication, checkpoint, and DNA damage response genes first identified in yeast have subsequently been identified in human cells, demonstrating the utility of this model system as well as the remarkable evolutionary conservation of these critical biological pathways.

The availability of sophisticated functional genomics tools in yeast allows the application of high-throughput methodologies, and the powerful genetics and experimental accessibility of yeast model systems affords the ability to combine in vitro studies with phenotypic analysis in vivo. In this way the identification, molecular characterization, and correlation of specific biochemical defects with functional defects in vivo can be carried out in a single model system.

DNA Replication

Our studies of DNA replication are proceeding on three fronts.

First, we are continuing our characterization of Rmi1, a novel component of the RecQ helicase-Topoisomerase III complex that we identified. Mutants lacking Rmi1 have a huge increase in spontaneous DNA damage, and this results in constitutive checkpoint acitivation and chromosomal rearrangements. We are examining the role of Rmi1 in DNA replication and determining the biochemical properties of Rmi1.

Secondly, we are determining the role of Csm3 in replication fork integrity and in the establishment of sister chromatid cohesion.

Thirdly, we are using functional genomics screens in budding yeast to identify novel regulators of DNA replication and of cell division cycle progression.

Genome Stability

Our current focus includes Elg1, which is important for DNA replication and is a suppressor of recombination, mutation, and chromosome loss and rearrangement. We have purified the Elg1-RFC complex to homogeneity in order to fully characterize its biochemical activity. Additionally, we are pursuing in vivo studies to define the nature of the defect in cells lacking Elg1.

In a second major effort we are identifying regulators and effectors of the S phase checkpoint response. To this end we have performed genome-wide synthetic genetic interaction and dosage suppression screens with checkpoint mutants, as well as screens for different types of genomic instability.

Finally, we are identifying the mechanism of action of Rtt107 in recovery from DNA damage during S phase. Rtt107 is a checkpoint kinase target, and we have recently found that Rtt107 phosphorylation is regulated by the nuclease subunit Slx4.