Multiple forms of DNA polymerase from the thermo-acidophilic eubacterium Bacillus acidocaldarius: purification,...

Two DNA polymerase isoenzymes, called DpA and DpB on the basis of their elution order from DEAE cellulose, were purified to homogeneity from the thermo-acidophilic eubacterium Bacillus acidocaldarius. The enzymes are weakly acidophilic proteins constituted by a single subunit of 117 and 103 kDa respectively. DpA and DpB differ in thermostability, in thermophilicity, in sensitivity to assay conditions and in resistance to sulphydryl-group blocking agents such as N-ethylmaleimide and p-hydroxymercuriobenzoate. They differ also in synthetic template-primer utilization, in the apparent Km for dNTPs and in processivity. In particular, DpA utilizes more effic iently synthetic templates-primers such as poly(dA).poly(dT), poly(dT). (rA)12-18 and poly(rA).(dT)12-18 and presents a greater tendency to accept dNTP analogues modified in the sugar or in the base ring, such as cytosine beta-d-arabinofuranoside 5'-triphosphate, 2',3'-dideoxyribonucleosides 5'-triphosphate, butylphenyl-dGTP and digoxigenin-conjugated dUTP. In addition, DpA presents an exonuclease activity that preferentially hydrolyses DNA in the 5'-3' direction, whereas DpB lacks this activity. The possible biological role of the enzymes is discussed.