PROJECT SUMMARY / ABSTRACT Mammals have evolved an extensive nuclear network of DNA replication and repair proteins that are tasked with amplifying and maintaining the fidelity of their genetic code. These signaling mechanisms are always active, surveying the genome to maintain its integrity in the face of attack from external abiotic factors (such as radiation and chemicals) and biotic factors (bacteria and viruses). To counter the sentinels of genome integrity, viral pathogens have evolved strategies to usurp these host replication and repair proteins for their own benefit. Viral strategies to hijack the nuclear compartment include: localizing to cellular sites of DNA damage, generating additional DNA breaks on the host, amplifying the cellular DNA damage signals and tethering themselves extra- chromosomally to DNA break sites to persist long-term. However, the mechanisms by which viruses carry out these pathogenic activities remain largely unknown. Better mechanistic understanding of how viruses dysregulate host DNA repair and replication pathways are essential for developing therapeutic interventions for human health. The goal of this research program is to understand how genome stability is impacted by viral pathogens by building on existing technologies to develop novel tools that will help us interrogate how replication and repair proteins are usurped, modified and leveraged by DNA viruses. We propose to answer fundamental questions about host genome stability that are utilized by viral pathogens for short-term and long-term benefit. We will determine how cellular signals are modulated on a global scale by DNA viruses and how these signals impact host replication proteins. We will then decipher how viruses utilize cellular signals to localize their proteins and genomes to cellular DNA break sites. Lastly, we will interrogate how cellular proteins are used by viruses to tether themselves in proximity to DNA break sites for long-term persistence. Not only are these fundamental discoveries, they also have the potential to inform cancer therapies and human DNA repair in addition to generating knowledge about viral life cycles. These basic studies on viruses and DNA damage will benefit a diverse array of biologists who study viral signaling in the biosphere. These strong foundational methodologies can be applied broadly to study all eukaryotic viruses as well as bacteriophages.