ISG15 and HIV-1 infection: Similarly, small interfering RNA (siRNA) was used to deplete OTOF induced by IFN-α, and we consistently observed that OTOF knockdown impaired the IFN-α-mediated suppression of HIV-1 infection in macrophages (Fig. S2A); however, OTOF knockdown exerted no effects on IFN-induced ISG-15 expression, indicating that OTOF depletion did not affect cellular response to IFN.