Abstract
Background
The DNA end joining protein, Ku, is essential in Non-Homologous End Joining in prokaryotes and eukaryotes. It was first discovered in eukaryotes and later by PSI blast, was discovered in prokaryotes. While Ku in eukaryotes is often a multi domain protein functioning in DNA repair of physiological and pathological DNA double stranded breaks, Ku in prokaryotes is a single domain protein functioning in pathological DNA repair in spores or late stationary phase. In this paper we have attempted to systematically search for Ku protein in different phyla of bacteria and archaea as well as in different kingdoms of eukarya.
Result
From our search of 116 sequenced bacterial genomes, only 25 genomes yielded at least one Ku sequence. From a comprehensive search of all NCBI archaeal genomes, we received a positive hit in 7 specific archaea that possessed Ku. In eukarya, we found Ku protein in 27 out of 59 species. Since the entire genome of all eukaryotic species is not fully sequenced this number could go up. We then drew a phylogenetic maximum likelihood tree to determine the ancestral relationship between Ku70 and Ku80 in eukaryotes and Ku in prokaryotes. Out tree revealed a common node for some archaeal Ku, Ku70 and Ku80.
Conclusion
This led us to hypothesize that Ku from archaea transferred through horizontal gene transfer onto neozoa and then duplicated to form Ku70 and Ku80. Additionally, we analyzed the domains of the different eukaryotic species to demonstrate that fusion, fission, terminal addition, terminal deletion, single domain loss, single domain emergence events during evolution.
Low Force Unfolding of a Single-Domain Protein by Parallel Pathways
