The study investigates the role of human CtIP in DNA double-strand break (DSB) processing and repair. CtIP is recruited to DSBs exclusively in the S/G2 phases of the cell cycle and is essential for DSB resection, which is crucial for recruiting RPA and ATR to DSB sites and activating the ATR checkpoint signaling pathway. CtIP physically and functionally interacts with the MRE11 complex, and both CtIP and MRE11 are required for efficient homologous recombination (HR) repair. The C-terminal region of CtIP displays sequence homology with Sae2, a protein involved in DSB processing in yeast, suggesting that CtIP and Sae2 are functional homologues. These findings highlight the conserved roles of CtIP-like proteins in controlling DSB resection, checkpoint signaling, and HR.The study investigates the role of human CtIP in DNA double-strand break (DSB) processing and repair. CtIP is recruited to DSBs exclusively in the S/G2 phases of the cell cycle and is essential for DSB resection, which is crucial for recruiting RPA and ATR to DSB sites and activating the ATR checkpoint signaling pathway. CtIP physically and functionally interacts with the MRE11 complex, and both CtIP and MRE11 are required for efficient homologous recombination (HR) repair. The C-terminal region of CtIP displays sequence homology with Sae2, a protein involved in DSB processing in yeast, suggesting that CtIP and Sae2 are functional homologues. These findings highlight the conserved roles of CtIP-like proteins in controlling DSB resection, checkpoint signaling, and HR.