The EBNA1
protein of Epstein-Barr virus (EBV) plays several important roles in EBV
latent infection, including activating DNA replication from the latent origin of replication (oriP) and activating the transcription of other latency genes within the EBV
chromatin. These functions require EBNA1 binding to the DS and FR elements within oriP, respectively, although how these interactions activate these processes is not clear. We previously identified interactions of EBNA1 with the related
nucleosome assembly
proteins NAP1 and TAF-I, known to affect the replication and transcription of other chromatinized templates. We have further investigated these interactions, showing that EBNA1 binds directly to
NAP1 and to the beta
isoform of TAF-I (also called SET) and that these interactions greatly increase the solubility of EBNA1 in vitro. These interactions were confirmed in EBV-infected cells, and
chromatin immunoprecipitation with these cells showed that
NAP1 and TAF-I both localized with EBNA1 to the FR
element, while only TAF-I was detected with EBNA1 at the DS
element. In keeping with these observations, alteration of the
NAP1 or TAF-Ibeta level by RNA interference and overexpression inhibited transcriptional activation by EBNA1 in FR reporter assays. In addition, EBNA1-mediated DNA replication was stimulated when TAF-I (but not
NAP1) was downregulated and was inhibited by TAF-Ibeta overexpression. The results indicate that the interaction of EBNA1 with
NAP1 and TAF-I is important for transcriptional activation and that EBNA1 recruits TAF-I to the DS
element, where it negatively regulates DNA replication.