DNA polymerase X (Pol X) from African swine fever virus is the smallest known nucleotide polymerase. It has extremely low fidelity and may act as a mutase to alter the viral genome. Although it lacks the canonical DNA binding domain of other nucleotide polymerases, Pol X binds DNA with very high affinity. It also bind dNTP substrates in the absence of template DNA. It has highest highest affinity for dGTP, which may contribute to its low fidelity and preference for making GG mismatches.
Maciejewski, M.W., Shin, R., Pan, B., Marintchev, A., Denninger, A., Mullen, M.A., Kang, C., Gryk, M.R. and Mullen, G.P. (2001) Solution structure of a viral DNA repair polymerase. Nature Structural Biology 8, 936-941.