specific loop in human DNA polymerase mu allows switching between creative and DNA-instructed synthesis

• Published in: Nucleic acids research Vol. 34; no. 16; pp. 4572 - 4582
• Main Authors: Juárez, Raquel, Ruiz, José F, McElhinny, Stephanie A. Nick, Ramsden, Dale, Blanco, Luis
• Format: Journal Article
• Language: English
• Published: England Oxford Publishing Limited (England) 01.09.2006; Oxford University Press
• Subjects: Amino Acid Sequence; Catalysis; Chimaera; DNA - biosynthesis; DNA - metabolism; DNA Nucleotidylexotransferase - chemistry; DNA, Single-Stranded - metabolism; DNA-Directed DNA Polymerase - chemistry; DNA-Directed DNA Polymerase - genetics; DNA-Directed DNA Polymerase - metabolism; Humans; Molecular Sequence Data; Nucleic Acid Enzymes; Protein Binding; Protein Structure, Tertiary; Sequence Deletion; Templates, Genetic
• ISSN: 0305-1048; 1362-4962
• DOI: 10.1093/nar/gkl457

Human DNA polymerase mu (Polμ) is a family X member that has terminal transferase activity but, in spite of a non-orthodox selection of the template information, displays its maximal catalytic efficiency in DNA-templated reactions. As terminal deoxynucleotidyl transferase (TdT), Polμ has a specific loop (loop1) that could provide this enzyme with its terminal transferase activity. When loop1 was deleted, human Polμ lacked TdT activity but improved DNA-binding and DNA template-dependent polymerization. Interestingly, when loop1 from TdT was inserted in Polμ (substituting its cognate loop1), the resulting chimaera displayed TdT activity, preferentially inserting dGTP residues, but had a strongly reduced template-dependent polymerization activity. Therefore, a specialized loop in Polμ, that could adopt alternative conformations, appears to provide this enzyme with a dual capacity: (i) template independency to create new DNA information, in which loop1 would have an active role by acting as a 'pseudotemplate'; (ii) template-dependent polymerization, in which loop1 must allow binding of the template strand. Recent in vivo and in vitro data suggest that such a dual capacity could be advantageous to resolve microhomology-mediated end-joining reactions.