title: Calcium is a cofactor of polymerization but inhibits pyrophosphorolysis by the Sulfolobus solfataricus DNA polymerase Dpo4.
abstract: Y-Family DNA polymerase IV (Dpo4) from Sulfolobus solfataricus serves as a model system for eukaryotic translesion polymerases, and three-dimensional structures of its complexes with native and adducted DNA have been analyzed in considerable detail. Dpo4 lacks a proofreading exonuclease activity common in replicative polymerases but uses pyrophosphorolysis to reduce the likelihood of incorporation of an incorrect base. Mg(2+) is a cofactor for both the polymerase and pyrophosphorolysis activities. Despite the fact that all crystal structures of Dpo4 have been obtained in the presence of Ca(2+), the consequences of replacing Mg(2+) with Ca(2+) for Dpo4 activity have not been investigated to date. We show here that Ca(2+) (but not Ba(2+), Co(2+), Cu(2+), Ni(2+), or Zn(2+)) is a cofactor for Dpo4-catalyzed polymerization with both native and 8-oxoG-containing DNA templates. Both dNTP and ddNTP are substrates of the polymerase in the presence of either Mg(2+) or Ca(2+). Conversely, no pyrophosphorolysis occurs in the presence of Ca(2+), although the positions of the two catalytic metal ions at the active site appear to be very similar in mixed Mg(2+)/Ca(2+)- and Ca(2+)-form Dpo4 crystals.
authors: Department of Biochemistry and Center in Molecular Toxicology, Vanderbilt University, School of Medicine, Nashville, Tennessee 37232, USA.
authors: Adriana
authors: A
authors: Irimia
authors: Hong
authors: H
authors: Zang
authors: Lioudmila V
authors: LV
authors: Loukachevitch
authors: Robert L
authors: RL
authors: Eoff
authors: F Peter
authors: FP
authors: Guengerich
authors: Martin
authors: M
authors: Egli