Proliferating cell nuclear antigen (PCNA) is a key protein involved in DNA replication, repair, and cell cycle regulation. Initially identified as a DNA sliding clamp for replicative DNA polymerases, PCNA has since been shown to interact with numerous partners involved in various metabolic pathways, including Okazaki fragment processing, DNA repair, translesion synthesis, DNA methylation, chromatin remodeling, and cell cycle control. PCNA forms a homotrimer with a ring-like structure that allows it to encircle DNA while remaining able to slide along it. This structure enables PCNA to increase the processivity of DNA polymerases by interacting with their outer surface and tethering them to DNA. PCNA interacts with a variety of proteins, including DNA polymerases, DNA repair enzymes, and cell cycle regulators. These interactions are crucial for coordinating DNA replication, repair, and cell cycle progression. For example, PCNA plays a central role in DNA replication by facilitating the switch from DNA polymerase α to DNA polymerase δ or ε. It also participates in DNA repair processes such as nucleotide excision repair, base excision repair, and mismatch repair. PCNA is involved in the recruitment of repair proteins to sites of DNA damage and in the coordination of repair activities. In addition to DNA repair, PCNA is involved in cell cycle control by interacting with cyclin-CDK complexes and CDK inhibitors such as p21. These interactions help regulate the progression of the cell cycle and ensure proper DNA replication and repair. PCNA also plays a role in chromatin metabolism, sister chromatin cohesion, and apoptosis. It is involved in the maintenance of chromatin structure, the coordination of DNA replication and repair, and the regulation of cell death. PCNA's ability to interact with multiple partners suggests that it acts as a central hub for coordinating various cellular processes. The interactions between PCNA and its partners are regulated by post-translational modifications and the dynamic localization of these proteins within the cell. Understanding the mechanisms by which PCNA coordinates these interactions is essential for elucidating the complex network of processes that ensure accurate DNA replication and repair.Proliferating cell nuclear antigen (PCNA) is a key protein involved in DNA replication, repair, and cell cycle regulation. Initially identified as a DNA sliding clamp for replicative DNA polymerases, PCNA has since been shown to interact with numerous partners involved in various metabolic pathways, including Okazaki fragment processing, DNA repair, translesion synthesis, DNA methylation, chromatin remodeling, and cell cycle control. PCNA forms a homotrimer with a ring-like structure that allows it to encircle DNA while remaining able to slide along it. This structure enables PCNA to increase the processivity of DNA polymerases by interacting with their outer surface and tethering them to DNA. PCNA interacts with a variety of proteins, including DNA polymerases, DNA repair enzymes, and cell cycle regulators. These interactions are crucial for coordinating DNA replication, repair, and cell cycle progression. For example, PCNA plays a central role in DNA replication by facilitating the switch from DNA polymerase α to DNA polymerase δ or ε. It also participates in DNA repair processes such as nucleotide excision repair, base excision repair, and mismatch repair. PCNA is involved in the recruitment of repair proteins to sites of DNA damage and in the coordination of repair activities. In addition to DNA repair, PCNA is involved in cell cycle control by interacting with cyclin-CDK complexes and CDK inhibitors such as p21. These interactions help regulate the progression of the cell cycle and ensure proper DNA replication and repair. PCNA also plays a role in chromatin metabolism, sister chromatin cohesion, and apoptosis. It is involved in the maintenance of chromatin structure, the coordination of DNA replication and repair, and the regulation of cell death. PCNA's ability to interact with multiple partners suggests that it acts as a central hub for coordinating various cellular processes. The interactions between PCNA and its partners are regulated by post-translational modifications and the dynamic localization of these proteins within the cell. Understanding the mechanisms by which PCNA coordinates these interactions is essential for elucidating the complex network of processes that ensure accurate DNA replication and repair.