The DNA segregation mechanism of Epstein-Barr virus nuclear antigen 1

Latent Epstein-Barr virus (EBV) genomes are maintained in human cells as lo w copy number episomes that are thought to be partitioned by attachment to the cellular mitotic chromosomes through the viral EBNA1 protein. We have i dentified a human protein, EBP2, which interacts with the EBNA1 sequences t hat govern EBV partitioning. Here we show that, in mitosis, EBP2 localizes to the condensed cellular chromosomes producing a staining pattern that is indistinguishable from that of EBNA1. The localization of EBNA1 proteins wi th mutations in the EBP2 binding region was also examined. An EBNA1 mutant (Delta 325-376) disrupted for EBP2 binding and segregation function was nuc lear but failed to attach to the cellular chromosomes in mitosis. Our resul ts indicate that amino acids 325-376 mediate the binding of EBNA1 to mitoti c chromosomes and strongly suggest that EBNA1 mediates EBV segregation by a ttaching to EBP2 on the cellular mitotic chromosomes.