UBE2N and viral infectious disease: While we do not find a requirement for ubiquitination activity in TRIM5α restriction of viral infection (Figs1 and 4), our data are compatible with a model in which TRIM5α synthesizes unanchored polyUb, as we too observed unanchored polyUb chain synthesis in vitro using recombinant TRIM5α and either Ube2N/Ube2V2 or Ube2N/Ube2V1 (Fig 5).