Plays an important role in the establishment of B-cell immortalization by acting as an EBNA2 coactivator. This transcriptional activation preferentially enhances the expression of the major viral protein LMP1. The interaction between EBNA-LP and host SP100 correlates with coactivation of EBNA2 and the relocalization of SP100 from PML nuclear bodies into nucleoplasm. Homooligomer. Interacts with host SP100; this interaction is important for EBNA-LP coactivator activity. Interacts with host HAX1, ERR1 and HSPA2. Interacts with host PRKDC and AKAP8L; these interactions modulate the coactivator function of EBNA-LP. Phosphorylated by the cellular protein kinase cdc2. Belongs to the lymphocryptovirus EBNA-LP family.