InterPro domain: IPR038654

This entry represents the PINIT domain found in the Siz/PIAS RING family of SUMO E3 ligases [ 1 ]. These proteins present a tripartite architecture with an N-terminal PINIT domain, a central zinc-containing RING-like SP-RING domain, and a C-terminal domain desginated SP-CTD. Structural and biochemical studies have shown that both SP-RING and SP-CTD are required for activation of the E2-SUMO thioester while the PINIT domain is required for redirecting SUMO conjugation to the proliferating cell nuclear antigen (PCNA) at lysine 164, a non-consensus lysine residue that is not modified by the SUMO E2 in the absence of Siz1 [ 2 ].

1. The 'PINIT' motif, of a newly identified conserved domain of the PIAS protein family, is essential for nuclear retention of PIAS3L. FEBS Lett. 554, 111-8
2. Structure of the Siz/PIAS SUMO E3 ligase Siz1 and determinants required for SUMO modification of PCNA. Mol. Cell 35, 669-82