The Novel Nuclear Targeting and BFRF1-Interacting Domains of BFLF2 Are Essential for Efficient Epstein-Barr Virus Virion Release

Abstract

Although Epstein-Barr virus (EBV) BFRF1 and BFLF2 are homologs of conserved viral nuclear egress complex (NEC) in all human herpesviruses, unique amino acid sequences and functions were identified in both proteins. In this study, the nuclear targeting and BFRF1-interacting domains were found within the N terminus of BFLF2. We showed that amino acids (aa) 82 to 106 are the major region required for BFLF2 to interact with BFRF1. However, the coimmunoprecipitation (Co-IP) data and glutathione transferase (GST) pulldown experiments revealed that multiple regions of both proteins contribute to reciprocal interactions. Different from the canonical nuclear localization signal (NLS) in other herpes viral homologs, BFLF2 contains a novel importin-dependent nuclear localization signal, including R47, K50, and R52 and several neighboring discontinuous arginine and histidine residues. Using a bacmid complementation system, we show that both the nuclear targeting and the novel nuclear localization signal within aa 82 to 106 of BFLF2 are required for virion secretion.