DNA polymerase X of African swine fever virus: insertion fidelity on gapped DNA substrates and AP lyase activity support a role in base excision repair of viral DNA.


DNA polymerase X (pol X) from African swine fever virus (ASFV) is the smallest naturally ocurring DNA-directed DNA polymerase (174 amino acid residues) described so far. Previous biochemical analysis has shown that ASFV pol X is a highly distributive, monomeric enzyme, lacking a proofreading 3'-5' exonuclease. Also, ASFV pol X binds intermediates of the single-nucleotide base excision repair (BER) process, and is able to efficiently repair single-nucleotide gapped DNA. In this work, we perform an extensive kinetic analysis of single correct and incorrect nucleotide insertions by ASFV pol X using different DNA substrates: (i) a primer/template DNA; (ii) a 1nt gapped DNA; (iii) a 5'-phosphorylated 1nt gapped DNA. The results obtained indicate that ASFV pol X exhibits a general preference for insertion of purine deoxynucleotides, especially dGTP opposite template C. Moreover, ASFV pol X shows higher catalytic efficiencies when filling in gapped substrates, which are increased when a phosphate group is present at the 5'-margin of the gap. Interestingly, ASFV pol X misinserts nucleotides with frequencies from 10(-4) to 10(-5), and the insertion fidelity varies depending on the substrate, being more faithful on a phosphorylated 1nt gapped substrate. We have analyzed the capacity of ASFV pol X to act on intermediates of BER repair. Although no lyase activity could be detected on preincised 5'-deoxyribose phosphate termini, ASFV pol X has lyase activity on unincised abasic sites. Altogether, the results support a role for ASFV pol X in reparative BER of damaged viral DNA during ASFV infection.



Exonuclease Activity, Fidelity, Source / Purification, Nucleotide Incorporation


new topics/pols set partial results complete validated


Polymerase Reference Property Result Context
ASFV pol X García-Escudero R2003 3-5' Exonuclease (proofreading) No
ASFV pol X García-Escudero R2003 Overall Error Rate 0.00024 errors/bp
ASFV pol X García-Escudero R2003 Full length or truncated Full length
ASFV pol X García-Escudero R2003 Gap Filling Yes

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