title: Accuracy of Deoxynucleotide Incorporation by Soybean Chloroplast DNA Polymerases Is Independent of the Presence of a 3[prime] to 5[prime] Exonuclease.
abstract: DNA polymerase was purified from soybean (Glycine max) chloroplasts that were actively replicating DNA. The main form (form I) of the enzyme was associated with a low level of 3[prime] to 5[prime] exonuclease activity throughout purification, although the ratio of exonuclease to polymerase activity decreased with each successive purification step. A second form (form II) of DNA polymerase, which elutes from DEAE-cellulose at a higher salt concentration than form I, was devoid of any exonuclease activity. To assess the potential function of the 3[prime] to 5[prime] exonuclease in proofreading, the fidelity of deoxynucleotide incorporation was measured for form I DNA polymerase throughout purification. Despite the steadily decreasing ratio of 3[prime] to 5[prime] exonuclease to polymerase activity, the extent of misincorporation by form I enzyme remained unchanged during the final purification steps, suggesting that the exonuclease did not contribute to the accuracy of DNA synthesis by this polymerase. Fidelity of form I DNA polymerase, when compared with that of form II, revealed a higher level of misincorporation for form I enzyme, a finding that is consistent with the exonuclease playing little or no role in exonucleolytic proofreading.
authors.affiliation: Department of Chemistry and Biochemistry, University of Southern Mississippi, Hattiesburg, Mississippi 39406.
authors.forename: J. C.
authors.initials: JC
authors.lastname: Bailey
authors.forename: S.
authors.initials: S
authors.lastname: Heinhorst
authors.forename: G. C.
authors.initials: GC
authors.lastname: Cannon