EC 2.3.2.36     
Accepted name: RING-type E3 ubiquitin transferase (cysteine targeting)
Reaction: [E2 ubiquitin-conjugating enzyme]-S-ubiquitinyl-L-cysteine + [acceptor protein]-L-cysteine = [E2 ubiquitin-conjugating enzyme]-L-cysteine + [acceptor protein]-S-ubiquitinyl-L-cysteine
Glossary: RING = Really Interesting New Gene
Other name(s): RING E3 ligase (misleading)
Systematic name: [E2 ubiquitin-conjugating enzyme]-S-ubiquitinyl-L-cysteine:[acceptor protein] ubiquitin transferase (thioester bond-froming; RING-type)
Comments: This relatively rare subpopulation of RING-type E3 ubiquitin transferases (cf. EC 2.3.2.27), found in mammals and herpes viruses, can transfer ubiquitin to a cysteine residue in target proteins. Additional ubiquitin molecules are polymerized on top of the initial ubiquitin molecule by formation of an isopeptide linkage with lysine48 in the pre-attached ubiquitin [2].
References:
1.  Cadwell, K. and Coscoy, L. Ubiquitination on nonlysine residues by a viral E3 ubiquitin ligase. Science 309 (2005) 127–130. [PMID: 15994556]
2.  Wang, Y.J., Bian, Y., Luo, J., Lu, M., Xiong, Y., Guo, S.Y., Yin, H.Y., Lin, X., Li, Q., Chang, C.CY., Chang, T.Y., Li, B.L. and Song, B.L. Cholesterol and fatty acids regulate cysteine ubiquitylation of ACAT2 through competitive oxidation. Nat. Cell Biol. 19 (2017) 808–819. [PMID: 28604676]
3.  Zhou, Z.S., Li, M.X., Liu, J., Jiao, H., Xia, J.M., Shi, X.J., Zhao, H., Chu, L., Liu, J., Qi, W., Luo, J. and Song, B.L. Competitive oxidation and ubiquitylation on the evolutionarily conserved cysteine confer tissue-specific stabilization of Insig-2. Nat. Commun. 11:379 (2020). [PMID: 31953408]
[EC 2.3.2.36 created 2020]