Cancer cells are genetically unstable and often contain high levels of DNA damage due to replication stress. This difference with normal cells presents an opportunity for therapeutic intervention using synthetic lethal approaches targeting the DNA damage response (DDR) and other genome maintenance pathways. Identification of key DDR proteins, characterizing their function in genome maintenance pathways, and defining the context where they become essential for viability is critical. The proposed studies will examine the genome maintenance activities of SMARCAL1, a recently discovered DDR protein. SMARCAL1 is an SNF2 family of ATPases that is activated by binding to forked DNA structures. SMARCAL1 has an unusual annealing helicase activity and functions at stalled replication forks. Our preliminary data support the hypothesis that SMARCAL1 functions with other DDR proteins to maintain genome integrity during DNA replication stress and thereby prevent disease. We will test this hypothesis by completing three specific aims: (1) characterize the interactions of SMARCAL1 with specific DDR proteins and determine the function of these interactions; (2) evaluate the in vivo function of SMARCAL1 in the response to DNA replication stress and damage; and (3) characterize the role of SMARCAL1 in responding to oncogene-induced replication stress. Innovative biochemical and genetic approaches including a unique mouse model of SMARCAL1-loss of function are proposed. Completion of this project will define the functional consequences of SMARCAL1 interaction with DDR proteins, and the in vivo function of SMARCAL1 in responding to both drug and oncogene-induced replication stress. Importantly, the project combines the complementary expertise of two investigators, who by working together, will provide critical insight into replication stress and the DDR and will identify novel therapeutic avenues to exploit in the treatment of cancer.