This family contains a number of eukaryotic cell division cycle 123 (Cdc123, also known as D123) proteins approximately 330 residues long. It has been shown that mutated variants of D123 exhibit temperature-dependent differences in their degradation rate [1]. D123 proteins are regulators of eIF2, the central regulator of translational initiation [2]. Family members include ATP-grasp enzymes belonging to the R2K clade, wherein one of the absolutely-conserved lysine residues has migrated to the RAGYNA domain which is a part of the core ATP-grasp module. This family is found in eukaryotes as well as NCDLVs and diverse bacteria. In eukaryotes, the domain is found in both the CDC123 enzymes and a related clade of proteins found in amoeboid organisms, while in bacteria it is observed embedded in polymorphic toxin loci [3].

1: Reversion of temperature-sensitive mutation by inhibition of proteasome-mediated degradation of mutated D123 protein. Okuda A, Ohtsu M, Kimura G; Cell Struct Funct 2001;26:205-214. PMID:11699637

2: Cdc123 and checkpoint forkhead associated with RING proteins control the cell cycle by controlling eIF2gamma abundance. Bieganowski P, Shilinski K, Tsichlis PN, Brenner C; J Biol Chem 2004; [Epub ahead of print] PMID:15319434

3: The eukaryotic translation initiation regulator CDC123 defines a divergent clade of ATP-grasp enzymes with a predicted role in novel protein modifications. Burroughs AM, Zhang D, Aravind L; Biol Direct. 2015;10:21. PMID:25976611