This family represents a conserved region approximately 100 residues long within mammalian hepatocellular carcinoma-associated antigen 59 (HCA59) [1]. Family members are found in a variety of eukaryotes, such as fission yeast where telomere length and silencing protein 1 (Tls1) is required for telomeric heterochromatin assembly as well as telomere length control [2]. Homologs in Arabidopsis are known as Cop1 suppressor 2 (CSU2). Csu2 inhibits constitutive photomorphogenic 1 (COP1) E3 ubiquitin ligase activity. Furthermore, CSU2 is required for primary root development under normal light growth condition [3].

1: Large scale identification of human hepatocellular carcinoma-associated antigens by autoantibodies. Wang Y, Han KJ, Pang XW, Vaughan HA, Qu W, Dong XY, Peng JR, Zhao HT, Rui JA, Leng XS, Cebon J, Burgess AW, Chen WF; J Immunol. 2002;169:1102-1109. PMID:12097419

2: Tls1 regulates splicing of shelterin components to control telomeric heterochromatin assembly and telomere length. Wang J, Tadeo X, Hou H, Andrews S, Moresco JJ, Yates JR 3rd, Nagy PL, Jia S; Nucleic Acids Res. 2014;42:11419-11432. PMID:25245948

3: Arabidopsis COP1 SUPPRESSOR 2 Represses COP1 E3 Ubiquitin Ligase Activity through Their Coiled-Coil Domains Association. Xu D, Lin F, Jiang Y, Ling J, Hettiarachchi C, Tellgren-Roth C, Holm M, Wei N, Deng XW; PLoS Genet. 2015;11:e1005747. PMID:26714275