Replication from oriP of Epstein-Barr virus requires human ORC and is inhibited by geminin

A hypomorphic mutation made in the ORC2 gene of a human cancer cell line th rough homologous recombination decreased Orc2 protein levels by 90%. The G1 phase of the cell cycle was prolonged, but there was no effect on the util ization of either the c-Myc or beta -globin cellular origins of replication . Cells carrying this mutation failed to support the replication of a plasm id bearing the oriP replicator of Epstein Barr virus (EBV), and this defect was rescued by reintroduction of Orc2. Orc2 specifically associates with o riP in cells, most likely through its interaction with EBNA1. Geminin, an i nhibitor of the mammalian replication initiation complex, inhibits replicat ion from oriP. Therefore, ORC and the human replication initiation apparatu s is required for replication from a viral origin of replication.