Epstein-Barr nuclear antigen 1 binds and destabilizes nucleosomes at the viral origin of latent DNA replication

The EBNA1 protein of Epstein-Barr virus (EBV) activates latent-phase DNA re plication by an unknown mechanism that involves binding to four recognition sites in the dyad symmetry (DS) element of the viral latent origin of DNA replication. Since EBV episomes are assembled into nucleosomes, we have exa mined the ability of Epstein-Barr virus nuclear antigen 1 (EBNA1) to intera ct with the DS element when it is assembled into a nucleosome core particle . EBNA1 bound to its recognition sites within this nucleosome, forming a te rnary complex, and displaced the histone octamer upon competitor DNA challe nge. The DNA binding and dimerization region of EBNA1 was sufficient for nu cleosome binding and destabilization. Although EBNA1 was able to bind to nu cleosomes containing two recognition sites from the DS element positioned a t the edge of the nucleosome, nucleosome destabilization was only observed when all four sites of the DS element were present. Our results indicate th at the presence of a nucleosome at the viral origin will not prevent EBNA1 binding to its recognition sites. In addition, since four EBNA1 recognition sites are required for both nucleosome destabilization and efficient origi n activation, our findings also suggest that nucleosome destabilization by EBNA1 is important for origin activation.