| Type: | Family | Name: | Non-homologous end joining protein Ku, prokaryotic type |
| Description: | This superfamily consists of prokaryotic Ku domain containing proteins. In the eukaryotes it has been shown that the Ku protein is involved in repairing DNA double-strand breaks by non-homologous end-joining [, ]. The Ku protein is a heterodimer of approximately 70 kDa and 80 kDa subunits []. Both these subunits have strong sequence similarity and it has been suggested that they may have evolved by gene duplication from a homodimeric ancestor in eukaryotes []. The prokaryotic Ku members are homodimers and they have been predicted to be involved in the DNA repair system, which is mechanistically similar to eukaryotic non-homologous end joining [, ]. Recent findings have implicated yeast Ku in telomeric structure maintenance in addition to on-homologous end-joining. Some of the phenotypes of the Ku-knockout mice may indicate a similar role for Ku at mammalian telomeres [].Evolutionary notes: With current available phyletic information it is difficult to determine the correct evolutionary trajectory of the Ku domain. It is possible that the core Ku domain was present in bacteria and archaea even before the presence of the eukaryotes. Eukaryotes might have vertically inherited the Ku-core protein, from a common ancestor shared with a certain archaeal lineage or through horizontal transfer from bacteria. Alternatively, the core Ku domain could have evolved in the eukaryotic lineage and then horizontally transferred to the prokaryotes. Sequencing of additional archaeal genomes and those of early-branching eukaryotes may help resolving the evolutionary history of the Ku domain.Structure notes: The eukaryotic Ku heterodimer comprises an alpha/beta N-terminal, a central beta-barrel domain and a helical C-terminal arm []. Structural analysis of the Ku70/80 heterodimer bound to DNA indicate that subunit contacts lead to the formation of a highly charged channel through which the DNA passes without making any contacts with the DNA bases [].For additional information please see []. | Short Name: | Prok_Ku |
