Function of Cdc45 in DNA Replication and in Response to Genotoxic Stress

DNA replication is a highly conserved and tightly regulated process, with a variety of factors acting to ensure faithful duplication and stability of chromosomal DNA. During replication, positive supercoils form ahead of the advancing replication fork. DNA topoisomerase 1 (Top1) acts to prevent DNA damage by relieving the torsional strain created by these supercoils. The camptothecin (CPT) class of chemotherapeutics target Top1, creating a long-lived DNA-Top1-CPT covalent complex, which leads to S-phase specific DNA lesions and cellular death. Our lab previously performed a genetic screen to isolate mutant proteins that enhanced cell sensitivity to Top1-mediated DNA damage. One of the mutant proteins identified was Cdc45G510E, which contains a single amino substitution at residue G510. Cells expressing this protein were also hypersensitive to other forms of DNA damage and exhibited collapsed replication forks, suggesting a role for Cdc45 in protecting cells from genotoxic stress. Cdc45 is an essential pro...