Role of the LEXE Motif of Protein-primed DNA Polymerases in the Interaction with the Incoming Nucleotide |
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Authors: | Eugenia Santos José M Lázaro Patricia Pérez-Arnaiz Margarita Salas Miguel de Vega |
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Institution: | From the Instituto de Biología Molecular “Eladio Viñuela” (Consejo Superior de Investigaciones Científicas), Centro de Biología Molecular “Severo Ochoa” (Consejo Superior de Investigaciones Científicas-Universidad Autónoma de Madrid), C/Nicolás Cabrera 1, Universidad Autónoma, Cantoblanco, 28049 Madrid, Spain |
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Abstract: | The LEXE motif, conserved in eukaryotic type DNA polymerases, is placed close to the polymerization active site. Previous studies suggested that the second Glu was involved in binding a third noncatalytic ion in bacteriophage RB69 DNA polymerase. In the protein-primed DNA polymerase subgroup, the LEXE motif lacks the first Glu in most cases, but it has a conserved Phe/Trp and a Gly preceding that position. To ascertain the role of those residues, we have analyzed the behavior of mutants at the corresponding φ29 DNA polymerase residues Gly-481, Trp-483, Ala-484, and Glu-486. We show that mutations at Gly-481 and Trp-483 hamper insertion of the incoming dNTP in the presence of Mg2+ ions, a reaction highly improved when Mn2+ was used as metal activator. These results, together with previous crystallographic resolution of φ29 DNA polymerase ternary complex, allow us to infer that Gly-481 and Trp-483 could form a pocket that orients Val-250 to interact with the dNTP. Mutants at Glu-486 are also defective in polymerization and, as mutants at Gly-481 and Trp-483, in the pyrophosphorolytic activity with Mg2+. Recovery of both reactions with Mn2+ supports a role for Glu-486 in the interaction with the pyrophosphate moiety of the dNTP. |
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Keywords: | Bacteriophage DNA Polymerase DNA Replication Nucleic Acid Synthesis Viral Polymerase |
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