SP-RING finger found in Saccharomyces cerevisiae E3 SUMO-protein ligase SIZ1, SIZ2, and similar proteins
Saccharomyces cerevisiae SIZ proteins, also known as SAP and Miz-finger domain-containing proteins, are Siz/PIAS RING (SP-RING) family SUMO E3 ligases, and may be involved in a novel pathway of chromosome maintenance. They enhance SUMO modification with many substrates in vivo, but also exhibit unique substrate specificity. SIZ1, also known as ubiquitin-like protein ligase 1 (Ull1), modifies both cytoplasmic and nuclear proteins. It functions as an E3 factor specific for septin components. SIZ1-dependent substrates include Cdc3 and Cdc11 (septin subunits), Prp45 (a splicing factor), and the proliferating cell nuclear antigen (PCNA). SIZ2, also known as NFI1, interacts with Smt3, SUMO/Smt3 conjugating enzyme Ubc9, and a septin component Cdc3. Members of this subfamily contain an N-terminal SAP (scaffold attachment factor A/B (SAF-A/B), acinus and PIAS) box with the LXXLL signature, a PINT motif, a specific RING finger known as Siz/PIAS (protein inhibitor of activated signal transducer and activator of transcription) RING (SP-RING) finger, and an acidic C-terminal domain. The SP-RING finger is a variant of RING finger, which lacks the second, fifth, and sixth zinc-binding residues of the consensus C3H2C3-/C3HC4-type RING fingers. It binds a single Zn ion, instead of two ions bound by typical RING fingers.
Comment:based on the structures of human Sumo ligases Pias2 and Pias3 with bound Zn2+ ion through their SP-RING fingers
Comment:The SP-RING finger is a variant of RING finger; it binds a single Zn ion and lacks the second, fifth, and sixth zinc-binding residues of the consensus C3H2C3-/C3HC4-type RING fingers.
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