This is the C-terminal domain found in EndoG-like mitochondrial endo/exonuclease (EXOG) proteins in higher eukaryotes. Evolutionary conserved mitochondrial nucleases are involved in programmed cell death and normal cell proliferation in lower and higher eukaryotes. It has been proposed that during metazoan evolution duplication of an ancestral nuclease gene could have generated the paralogous EndoG- and EXOG-protein subfamilies in higher eukaryotes, thereby maintaining the full endo/exonuclease activity found in mitochondria of lower eukaryotes. Family members include the human EXOG, a dimeric mitochondrial enzyme that displays 5'-3' exonuclease activity and further differs from EndoG in substrate specificity. This C-terminal domain is predicted to fold into a coiled-coil structure. Deletion of the domain led to a pronounced reduction in EXOG activity, revealing that the presence and most likely the proper positioning of this domain in EXOG proteins is crucial for its enzymatic activity [1].

1: EXOG, a novel paralog of Endonuclease G in higher eukaryotes. Cymerman IA, Chung I, Beckmann BM, Bujnicki JM, Meiss G; Nucleic Acids Res. 2008;36:1369-1379. PMID:18187503