This is the RING finger domain of Sina and its homologues from animals, Sinah1/2 and plants, such as SINAT3 from Arabidopsis [3]. Sina (seven in absentia) was first identified in Drosophila and is essential for the determination of the R7 pathway in photoreceptor cell development. It consists of a RING zinc finger at the N-terminal, followed by two zinc finger (C2H2 type) domains (Pfam:PF21361) and a C-terminal TRAF-like domain (Pfam:PF03145) [1,2]. This domain gives the E3 ubiquitin ligase activity to these proteins.

1: Two high-resolution structures of the human E3 ubiquitin ligase Siah1. Rimsa V, Eadsforth TC, Hunter WN; Acta Crystallogr Sect F Struct Biol Cryst Commun. 2013;69:1339-1343. PMID:24316825

2: Elucidation of the substrate binding site of Siah ubiquitin ligase. House CM, Hancock NC, Moller A, Cromer BA, Fedorov V, Bowtell DD, Parker MW, Polekhina G; Structure. 2006;14:695-701. PMID:16615911

3: SINAT E3 Ubiquitin Ligases Mediate FREE1 and VPS23A Degradation to Modulate Abscisic Acid Signaling. Xia FN, Zeng B, Liu HS, Qi H, Xie LJ, Yu LJ, Chen QF, Li JF, Chen YQ, Jiang L, Xiao S; Plant Cell. 2020;32:3290-3310. PMID:32753431