The Epstein-Barr nuclear antigen-1 (EBNA1) protein of Epstein-Barr virus is important for the replication, segregation, and transcriptional activation of latent Epstein-Barr virus genomes; has been implicated in host cell immortalization; and avoids proteasomal processing and cell-surface presentation. To gain insight into how EBNA1 fulfills these functions, we have profiled cellular protein interactions with EBNA1 using EBNA1 affinity chromatography and tandem affinity purification (TAP) of EBNA1 complexes from human cells (TAP-tagging). We discovered several new specific cellular protein interactions with EBNA1, including interactions with HAUSP/USP7, NAP1, template-activating factor-I beta/SET, CK2, and PRMT5, all of which play important cell regulatory roles. The ubiquitin-specific protease USP7 is a known target of herpes simplex virus, and the USP7-binding region of EBNA1 was mapped to amino acids 395-450. A mutation in EBNA1 that selectively disrupted binding to USP7 was found to cause a 4-fold increase in EBNA1 replication activity but had no effect on EBNA1 turnover and cell-surface presentation. The results suggest that USP7 can regulate the replication function of EBNA1 and that EBNA1 may influence cellular events by sequestering key regulatory proteins.