The seven in absentia (sina) gene was first identified in Drosophila. The Drosophila Sina protein is essential for the determination of the R7 pathway in photoreceptor cell development: the loss of functional Sina results in the transformation of the R7 precursor cell to a non- neuronal cell type. The Sina protein contains an N-terminal RING finger domain, through which it binds E2 ubiquitin-conjugating enzymes (UbcD1). Sina also interacts with Tramtrack (TTK88) via PHYL. Tramtrack is a transcriptional repressor that blocks photoreceptor determination, while PHYL down-regulates the activity of TTK88. In turn, the activity of PHYL requires the activation of the Sevenless receptor tyrosine kinase, a process essential for R7 determination. It is thought that thus Sina targets TTK88 for degradation, therefore promoting the R7 pathway. Murine and human homologues of Sina have also been identified, namely siah1/2. Siah-1 [1,4,5] also binds E2 enzymes (UbcH5) and through a series of physical interactions, targets beta-catenin for ubiquitin degradation. Siah-1 expression is enhanced by p53, itself promoted by DNA damage. Thus this pathway links DNA damage to beta-catenin degradation [2,3]. Sina proteins, therefore, physically interact with a variety of proteins. Following the RING domain, these proteins have two zinc fingers and a TRAF-like domain, involved in interactions with other proteins. In addition to the Drosophila protein and mammalian homologues, this family also includes homologues from Caenorhabditis elegans and Arabidopsis thaliana [6]. This entry represents the C-terminal TRAF-like domain.

1: Characterization of human homologs of the Drosophila seven in absentia (sina) gene. Hu G, Chung YL, Glover T, Valentine V, Look AT, Fearon ER; Genomics 1997;46:103-111. PMID:9403064

2: PHYL acts to down-regulate TTK88, a transcriptional repressor of neuronal cell fates, by a SINA-dependent mechanism. Tang AH, Neufeld TP, Kwan E, Rubin GM; Cell 1997;90:459-467. PMID:9267026

3: Siah-1, SIP, and Ebi collaborate in a novel pathway for beta-catenin degradation linked to p53 responses. Matsuzawa SI, Reed JC; Mol Cell 2001;7:915-926. PMID:11389839

4: 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

5: 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

6: 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