UC San Diego

Genome instability can arise due to the accumulation of gross chromosomal rearrangements (GCRs). Specifically, translocations, deletions, and chromosome fusions are frequent events seen in cancers with genome instability. There are multiple pathways that prevent GCRs, including S -phase cell cycle checkpoints, homologous recombination, telomere maintenance, suppression of de novo telomere addition, chromatin assembly, and mismatch repair. One view is that defects in DNA replication are one of the main causes of genome instability. The work presented here analyzes the role of RNaseH2 in preventing genome instability. RNaseH2 is involved in resolution of RNA-DNA hybrid replication intermediates that arise during Okazaki fragment processing of lagging strand DNA replication. It has been suggested that persistence of RNA-DNA hybrids can lead to genome instability because they can become mutagenic and possibly form secondary structures. It is known that there are pathways required to prevent the formation of DNA damage and there are also pathways required for dealing with the DNA damage once it becomes present, but that ultimately, both are required for prevention of genome instability. RNaseH2 is thought to be involved in preventing the formation of DNA damage. The genetic analysis presented here on rnaseh2 mutants examined what happens when there are defects in the RNaseH2 pathway thought to prevent formation of DNA damage and in addition to that when there are also defects in the pathways that are thought to prevent the accumulation of DNA damage. Additional work was done to survey a list of enriched genes that encode proteins with roles in genome instability to identify novel cellular functions important for maintenance of genome stability. The results presented in this Dissertation highlight the importance of many diverse proteins that have different cellular roles important for maintaining genome stability.