MAMMALIAN PROLIFERATING CELL NUCLEAR ANTIGEN STIMULATES THE PROCESSIVITY OF 2 WHEAT EMBRYO DNA-POLYMERASES

Multiple DNA polymerases have been described in all organisms studied to date. Their specific functions are not easy to determine, except wh en powerful genetic and/or biochemical tools are available. However, t he processivity of a DNA polymerase could reflect the physiological ro le of the enzyme. In this study, analogies between plant and animal DN A polymerases have been investigated by analyzing the size of the prod ucts synthesized by wheat DNA polymerases A, B, CI, and CII as a measu re of their processivity. Thus, incubations have been carried out with poly(dA)-oligo(dT) as a template-primer under varying assay condition s. In the presence Of MgCl2, DNA polymerase A was highly processive, w hereas DNA polymerases B, CI, and CII synthesized much shorter product s. With MnCl2 instead Of MgCl2, DNA polymerase A was highly processive , DNA polymerases B and CII were moderately processive, and DNA polyme rase CI remained strictly distributive. The effect of calf thymus prol iferating cell nuclear antigen (PCNA) on wheat polymerases was studied as described for animal DNA polymerases. The high processivity of DNA polymerase A was PCNA independent, whereas both enzyme activity and p rocessivity of wheat DNA polymerases B and CII were significantly stim ulated by PCNA. On the other hand, DNA polymerase CI was not stimulate d by PCNA and, like animal DNA polymerase beta, was distributive in al l cases. From these results, we propose that wheat DNA polymerase A co uld correspond to a DNA polymerase alpha, DNA polymerases B and CII co uld correspond to the delta-like enzyme, and DNA polymerase CI could c orrespond to DNA polymerase beta.