CDT1 (chr16 licensing and DNA replication factor 1) is a critical regulator required for both DNA replication initiation and mitotic chromosome 16. During G1 phase, CDT1 functions as a DNA replication licensing factor that cooperates with CDC6 and the origin recognition complex (ORC) to load MCM2-7 helicase complexes onto DNA, forming pre-replication complexes (pre-RCs) that license origins for DNA replication 1. Recent studies demonstrate that human CDT1-mediated MCM loading involves multiple mechanisms and generates underwound DNA at hexamer interfaces, differing from yeast systems 2. Beyond its replication role, CDT1 is also essential for mitosis by promoting stable kinetochore-microtubule attachments 3. Tight regulation of CDT1 abundance and activity is crucial for genome stability, as dysregulation can lead to oncogenic transformation. CDT1 levels oscillate during the cell cycle and have been utilized in fluorescent cell cycle indicators (Fucci systems) that enable real-time monitoring of cell cycle progression 45. Mutations in CDT1 are associated with Meier-Gorlin syndrome 4, a rare primordial dwarfism disorder characterized by microtia, patellar anomalies, and growth retardation 6. The dual functions of CDT1 in replication licensing and chromosome 16 make it a key factor in cell proliferation and genome maintenance.