PLANT PHYSIOLOGY , Vol 102, Issue 1 107-114, Copyright © 1993 by American Society of Plant Biologists
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METABOLISM AND ENZYMOLOGY |
Mammalian Proliferating Cell Nuclear Antigen Stimulates the Processivity of Two Wheat Embryo DNA Polymerases
P. Laquel, S. Litvak and M. Castroviejo
Institut de Biochimie Cellulaire du Centre National de la Recherche Scientifique, 1 rue Camille Saint Saens, 33077 Bordeaux Cedex, France
Multiple DNA polymerases have been described in all organisms studied to
date. Their specific functions are not easy to determine, except when
powerful genetic and/or biochemical tools are available. However, the
processivity of a DNA polymerase could reflect the physiological role of
the enzyme. In this study, analogies between plant and animal DNA
polymerases have been investigated by analyzing the size of the products
synthesized by wheat DNA polymerases A, B, CI, and CII as a measure of
their processivity. Thus, incubations have been carried out with
poly(dA)-oligo(dT) as a template-primer under varying assay conditions. In
the presence of MgCl2, DNA polymerase A was highly processive, whereas DNA
polymerases B, CI, and CII synthesized much shorter products. With MnCl2
instead of MgCl2, DNA polymerase A was highly processive, DNA polymerases B
and CII were moderately processive, and DNA polymerase CI remained strictly
distributive. The effect of calf thymus proliferating 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 processivity of wheat DNA
polymerases B and CII were significantly stimulated by PCNA. On the other
hand, DNA polymerase CI was not stimulated by PCNA and, like animal DNA
polymerase [beta], was distributive in all cases. From these results, we
propose that wheat DNA polymerase A could correspond to a DNA polymerase
[alpha], DNA polymerases B and CII could correspond to the [delta]-like
enzyme, and DNA polymerase CI could correspond to DNA polymerase [beta].
