Plays an essential role for activation and immortalization of human B-cells. Represses transcription of viral promoters TP1 and Cp through interaction with host RBPJ, and inhibits EBNA2-mediated activation of these promoters. Since Cp is the promoter for all EBNA mRNAs, EBNA3A probably contributes to a negative autoregulatory control loop (By similarity). Interacts with human UCKL1. Interacts with host CTPB1; this interaction seems important for EBNA3-mediated transcriptional repression. Interacts with host RBPJ (By similarity). Associated with the nuclear matrix. Belongs to the herpesviridae EBNA-3 family.