Evolutionary loss of 8-oxo-G repair components among eukaryotes

These DNA repair enzymes are present in all large phylogenetic groups, with MutM homologues being the most universally conserved. All chordates and echinoderms were found to possess all three 8-oxo-G repair components. Likewise, the red and green algae examined have all three repair enzymes, while all land-living plants have MutY and MutM homologues, but lack MutT. However, for some phyla, e.g. protostomes, a more patchy distribution was found. Nematodes provide a striking example, where Caenorhabditis is the only identified example of an organism group having none of the three repair enzymes, while the genome of another nematode, Trichinella spiralis, instead encodes all three. The most complex distribution exists in fungi, where many different patterns of retention or loss of the three repair components are found. In addition, we found sequence insertions near or within the catalytic sites of MutY, MutM, and MutT to be present in some subgroups of Ascomycetes.The 8-oxo-G repair enzymes are ancient in origin, and loss of individual 8-oxo-G repair components at several distinct points in evolution appears to be the most likely explanation for the phylogenetic pattern among eukaryotes.To maintain structural integrity of DNA, organisms have developed DNA repair mechanisms. These have evolved both in complexity and specificity to ensure genomic integrity against the constant threats from damaging agents of endogenous and exogenous origins. Damage to DNA bases resulting from alkylation, oxidation, deamination, and UV-induced crosslinking, is mainly repaired by the base excision repair (BER) pathway, which is highly conserved throughout evolution and ubiquitously present in bacteria, archaea, and eukaryotes [1]. BER is the major pathway for repair of oxidative base damage, transcription-coupled repair (TCR) and mismatch repair (MMR) being important backup pathways. Moreover, several of the DNA glycosylases that initiate BER of oxidative damage have overlapping specificit