Mapping EBNA-1 domains involved in binding to metaphase chromosomes

The Epstein-Barr virus (EBV) genome can persist in dividing human B cells a s multicopy circular episomes. Viral episomes replicate in synchrony with h ost cell DNA and are maintained at a relatively constant copy number for a long time. Only two viral elements, the replication origin OriP and the EBN A-1 protein, are required for the persistence of viral genomes during laten cy. EBNA-1 activates OriP during the S phase and may also contribute to the partition and/or retention of viral genomes during mitosis. Indeed, EBNA-1 has been shown to interact with mitotic chromatin, Moreover, viral genomes are noncovalently associated with metaphase chromosomes. This suggests tha t EBNA-1 may facilitate the anchorage of viral genomes on cellular chromoso mes, thus ensuring proper partition and retention. In the present paper, we have investigated the chromosome-binding activity of EBV EBNA-1, herpesvir us papio (HVP) EBNA-1, and various derivatives of EBV EBNA-1, fused to a va riant of the green fluorescent protein, The results show that binding to me taphase chromosomes is a common property of EBV and HVP EBNA-1, Further stu dies indicated that at least three independent domains (CBS-1, -2, and -3) mediate EBNA-1 binding to metaphase chromosomes. In agreement with the anch orage model, two of these domains mapped to a region that has been previous ly demonstrated to be required for the long-term persistence of OriP-contai ning plasmids.