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Closed Access item A single tyrosine prevents insertion of ribonucleotides in the eukaryotic-type φ29 DNA polymerase

Authors:Bonnin, Ana
Lázaro, José M.
Blanco, Luis
Salas, Margarita
Keywords:φ29 DNA polymerase, Site directed mutagenesis, Ribonucleotides, Polymerase active site
Issue Date:2-Jul-1999
Citation:Journal of Molecular Biology 290(1): 241-251 (1999)
Abstract:Three conserved motifs (named A, B and C) have been proposed to form the polymerization active site in all classes of DNA-dependent polymerases. In eukaryotic-type (α-like) DNA polymerases, motif A is characterized by the consensus “Dx2SLYP”. Mutants in φ29 DNA polymerase residue Tyr254 of this conserved motif had been previously shown to be affected in dNTP binding. Here, we show that a single substitution of Tyr254 into a valine residue enables the enzyme to incorporate ribonucleotide substrates, without affecting its wild-type affinity for dNTPs. Whereas the wild-type enzyme preferred dNTPs more than two million-fold over rNTPs, the mutation of Tyr254 into valine reduced the discrimination for rNTPs up to 1000-fold. In addition to this discrimination mechanism, based on sugar selection, φ29 DNA polymerase is very inefficient when extending an RNA primer terminus, allowing its exonucleolytic degradation. These results indicate that the Tyr254 of φ29 DNA polymerase is responsible for the discrimination against the 2′-OH group of an incoming ribonucleotide. This is the first time that the invariant tyrosine residue of motif A is involved in ribo-versus deoxyribonucleotide discrimination in an eukaryotic-type DNA polymerase.
Publisher version (URL):http://dx.doi.org/10.1006/jmbi.1999.2900
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