Abstract: Previous studies revealed that DNA ligase Ⅲ was restricted to vertebrates and functioned in nucleus DNA repair and mitochondria DNA replication and repair. Although recent researches have reported that DNA ligase Ⅲ is also found in non-vertebrates, little attention has been devoted to the distribution and functional evolution of DNA ligase Ⅲ. To probe the functional evolution of DNA ligase Ⅲ, database searches, mitochondrial localization signal prediction (MLS) and functional conservation analysis were performed. The results show that, DNA ligase Ⅲ can be observed in amoebozoa, metazoa and choanoflagellates, but the whole protein or some domains are lost in some species including fungi. The MLS prediction analysis suggests that, the DNA ligase Ⅲ in many species can not function in mitochondria, and is consequently less likely to play a role for DNA ligase Ⅲ in mitochondria. The conservation analyses of functional site demonstrate that nucleus DNA repair is an ancient and conserved function of DNA ligase Ⅲ.

Key words: DNA ligase Ⅲ, mitochondria localization signal, ZnF, BRCT, functional evolution