CHARACTERIZATION OF AN AFRICAN SWINE FEVER VIRUS 20-KDA DNA-POLYMERASE INVOLVED IN DNA-REPAIR

African swine fever virus (ASFV) encodes a novel DNA polymerase, const ituted of only 174 amino acids, belonging to the polymerase (pol) X fa mily of DNA polymerases. Biochemical analyses of the purified enzyme i ndicate that ASFV pol X is a monomeric DNA-directed DNA polymerase, hi ghly distributive, lacking a proofreading 3'-5'-exonuclease, and with a poor discrimination against dideoxynucleotides. A multiple alignment of family X DNA polymerases, together with the extrapolation to the c rystal structure of mammalian DNA polymerase beta (pol beta), showed t he conservation in ASFV pol X of the most critical residues involved i n DNA binding, nucleotide binding, and catalysis of the polymerization reaction. Therefore, the 20-kDa ASFV pol X most likely represents the minimal functional version of an evolutionarily conserved pol beta-ty pe DNA polymerase core, constituted by only the ''palm'' and ''thumb'' subdomains. It is worth noting that such an ''unfingered'' DNA polyme rase is able to handle templated DNA polymerization with a considerabl e high fidelity at the base discrimination level. Base excision repair is considered to be a cellular defense mechanism repairing modified b ases in DNA. Interestingly, the fact that ASFV pol X is able to conduc t filling of a single nucleotide gap points to a putative role in base excision repair during the ASFV life cycle.