Cloning, Expression, and Characterization of Family A DNA Polymerase from Massilia aurea

Abstract

Mau DNA polymerase is a family A DNA polymerase isolated from Massilia aurea. In this study, a recombinant plasmid, His6-tagged Mau-pET28c, was constructed. His-tagged Mau was expressed in Escherichia coli Rosseta 2 (DE3) competent cells and, after optimization of purification conditions, was successfully isolated via a two-step purification system by Ni2+-chelating affinity chromatography followed by heparin affinity chromatography. The biochemical properties of Mau DNA polymerase were investigated next. This polymerase showed maximal polymerase activity at 30 °C, pH 8.4–8.8, 2–10 mM MgCl2, and 10–40 mM KCl. Kinetic parameters of correct and incorrect dNTP incorporation as well as DNA-binding affinity were determined too. KdNTPd,app values were found to be 16 µM for correct dNTP and 200–500 µM for incorrect dNTP. The kinetic parameter kcat turned out to be 0.2 s−1 for correct dNTP incorporation and an order of magnitude less for incorrect dNTP incorporation. It was demonstrated that Mau DNA polymerase has 5′→3′ and 3′→5′ exonuclease activities associated with the main activity.