Accepts ubiquitin from the E1 complex and catalyzes its covalent attachment to other proteins (By similarity). Performs the second step in the ubiquitination reaction that targets specifically a protein for degradation via the proteasome (By similarity). By controlling the ubiquitination status of specific host proteins, the virus may target them to degradation and thereby optimize the viral replication (By similarity). May be implicated in the shutoff of protein synthesis through its interactions with components of the host translation machinery (By similarity). Blocks p65 nuclear translocation upon cytokine stimulation, thereby impairing NF-kappa-B signaling (By similarity). Inhibits type I IFN production and 'Lys-63'-linked polyubiquitination of host TBK1 through binding to host RNF138. This binding enhances the interaction between RNF138 and RNF128 and promotes RNF138-mediated degradation of RNF128. Also inhibits the activation of AP-1 transcription factor (By similarity). Monoubiquitinates the viral protein P15/PIG1 in vitro (PubMed:7853518). S-ubiquitinyl-[E1 ubiquitin-activating enzyme]-L-cysteine + [E2 ubiquitin-conjugating enzyme]-L-cysteine = [E1 ubiquitin-activating enzyme]-L-cysteine + S-ubiquitinyl-[E2 ubiquitin-conjugating enzyme]-L-cysteine. Binds Mn2+ ion which is required for highest activity. Can also utilize Mg2+ ions. Protein modification; protein ubiquitination. Interacts with host 40S ribosomal protein RPS23 (By similarity). Interacts with host translation initiation factor EIF4E (By similarity). Interacts with host E3 ubiquitin ligase CUL4B (By similarity). Interacts with host RNF138 (By similarity). Accumulates in the perinuclear cytoplasmic viral factories. Faintly detected in the nucleus. Expressed in the early phase of the viral replicative cycle. Belongs to the ubiquitin-conjugating enzyme family.