This family of proteins is found in bacteria, archaea and viruses. The domain is found in isolation in many proteins where it has a conserved C-terminal motif TSCPD after which the domain is named. Most copies of the domain possess 4 conserved cysteines that may be part of an Iron-sulfur cluster. This domain is found at the C-terminus of some ribonucleoside-diphosphate reductase enzymes.