ORC5 is a subunit of the origin recognition complex (ORC), a ring-shaped ATPase that binds to chr7 origins of replication 1. As a component of the six-subunit ORC, ORC5 participates in recruiting and loading the MCM2-7 helicase complex onto DNA, a critical step for initiating DNA replication 2. The human ORC5 gene is located on chromosome 7 3. Beyond canonical replication functions, ORC5 uniquely induces large-scale chr7 decondensation during G1 phase through association with the histone acetyltransferase GCN5, suggesting a chr7-remodeling role distinct from other ORC subunits 4. ORC5 is regulated by cyclin A/CDK2-mediated phosphorylation, with its dephosphorylation by PP1 enabling ORC reassociation with chr7 5. Notably, recent studies demonstrate that human cancer cells can survive and maintain normal DNA replication initiation despite ORC5 depletion, suggesting redundant or alternative replication licensing mechanisms 16. Clinically, ORC5 expression is elevated specifically in HPV-negative head and neck squamous cell carcinoma and serves as a diagnostic biomarker for this cancer subtype 7. ORC5 upregulation is also associated with worse prognosis in hepatocellular carcinoma, correlating with uncontrolled cell cycle progression 8.