InterPro domain: IPR007699

The SGT1-specific (SGS) domain is a module of ~90 amino acids, which wasinitially identified in eukaryotic Sgt1 proteins [ 1 ]. It was latter also found in calcyclin-binding proteins [ 2 ]. The SGS domain has been shown to bind to proteins of the S100 family, which are thought to function as sensors of calcium ion concentration in the cell [ 3 ].

In budding yeasts, Sgt1 is required for both SCF (Skp1p/Cdc53p-Cullin-F-box)-mediated ubiquitination, cyclic AMP pathway activity and kinetochore function [ 3 ]. Its Schizosaccharomyces pombe homologue, Git7, is required for glucose and cyclic AMP signaling, cell wall integrity, and septation [ 4 ]. Its two homologues in Arabidopsis, SGT1a and SGT1b, can complement two yeast temperature-sensitive sgt1 mutant alleles, suggesting that fundamental cellular function(s) of yeast SGT1in SCF-mediated protein ubiquitylation. Moreover, SGT1a and SGT1b can act as cochaperones with HSP90 and HSC70 and function in regulating multiple resistance (R) genes and environmental responses [ 5 , 6 , 6 , 7 ]. The SGS domain of SGT1 is a key determinant of the HSC70-SGT1 association [ 8 ].

Calcyclin (S100A6) is a member of the S100A family of calcium binding proteins and appears to play a role in cell proliferation [ 8 ].

1. The RAR1 interactor SGT1, an essential component of R gene-triggered disease resistance. Science 295, 2073-6
2. Calcium-regulated interaction of Sgt1 with S100A6 (calcyclin) and other S100 proteins. J. Biol. Chem. 278, 26923-8
3. Sgt1p contributes to cyclic AMP pathway activity and physically interacts with the adenylyl cyclase Cyr1p/Cdc35p in budding yeast. Eukaryot Cell 1, 568-82
4. Schizosaccharomyces pombe Git7p, a member of the Saccharomyces cerevisiae Sgtlp family, is required for glucose and cyclic AMP signaling, cell wall integrity, and septation. Eukaryot Cell 1, 558-67
5. Regulatory role of SGT1 in early R gene-mediated plant defenses. Science 295, 2077-80
6. Role of SGT1 in the regulation of plant R gene signalling. Microbes Infect 5, 969-76
7. Interaction between SGT1 and cytosolic/nuclear HSC70 chaperones regulates Arabidopsis immune responses. Plant Cell 19, 4061-76
8. Calcyclin (S100A6) regulates pulmonary fibroblast proliferation, morphology, and cytoskeletal organization in vitro. J. Cell. Biochem. 88, 848-54