PLANT PHYSIOLOGY , Vol 109, Issue 2 645-650, Copyright © 1995 by American Society of Plant Biologists
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BIOCHEMISTRY AND ENZYMOLOGY |
Studies on the Processivity of Maize DNA Polymerase 2, an [alpha]-Type Enzyme
P. Coello and J. M. Vazquez-Ramos
Departamento de Bioquimica, Facultad de Quimica, Universidad Nacional Autonoma de Mexico, Avenida Universidad y Copilco, Mexico 04510, D.F., Mexico
This paper describes studies on the processivity of an [alpha]-type DNA
polymerase from maize (Zea mays L.) embryonic axes, designated as DNA
polymerase 2. Using poly(dA)/oligo(dT) as template, DNA polymerase 2 has a
processivity of 18 ([plus or minus]5) nucleotides incorporated, a value
much lower than that found for wheat [alpha]-type DNA polymerase (P.
Laquel, S. Litvak, M. Castroviejo [1993] Plant Physiol 102: 107-114).
Conditions that maximally stimulate enzyme activity, such as 100 mM KCl and
12 mM Mg2+, are strongly inhibitory of processivity and cause the enzyme to
become distributive under these conditions. Optimal concentrations for
processivity are 10 mM KCl and 1 to 2 mM Mg2+. Both enzyme activity and
processivity were found to be similar at different Mn2+ concentrations.
Both DNA polymerase 2 activity and processivity are greatly reduced by
spermine and N-ethylmaleimide. A distinguishing feature of processivity in
DNA polymerase 2 was the response to ATP, which not only stimulated
processivity by more than 2-fold, but also produced a distinctive pattern
in which the enzyme seemed to pause every 10 nucleotides, reaching a value
of 40 to 50 nucleotides incorporated. This pattern was observed in some,
but not all, heparin-Sepharose fractions with enzyme activity, suggesting
the possibility of different DNA polymerase 2 complexes.
