Interferon - stimulated gene 15 (Isg15) is a 15 kDa Ub - like protein. It is linked to proteins in much the same way as Ub, using the E1, E2, E3 cascade. U bE1L and UbcH8 are the specific E1 and E2, respectively, to mediate protein ISGylation. Several E3s have also been found. Isg15 is induced by type I interferons (IFNalpha/beta) and bacterial and viral infections. Studies are still being conducted to discover the biological functions of Isg15.
