title: A specific loop in human DNA polymerase mu allows switching between creative and DNA-instructed synthesis.
abstract: Human DNA polymerase mu (Polmu) 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), Polmu has a specific loop (loop1) that could provide this enzyme with its terminal transferase activity. When loop1 was deleted, human Polmu lacked TdT activity but improved DNA-binding and DNA template-dependent polymerization. Interestingly, when loop1 from TdT was inserted in Polmu (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 Polmu, 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.
authors.affiliation: Centro de Biología Molecular Severo Ochoa (CSIC-UAM), Campus Universidad Autónoma Canto Blanco, 28049 Madrid, Spain.
authors.forename: Raquel
authors.initials: R
authors.lastname: Juárez
authors.forename: José F
authors.initials: JF
authors.lastname: Ruiz
authors.forename: Stephanie A
authors.initials: SA
authors.lastname: Nick McElhinny
authors.forename: Dale
authors.initials: D
authors.lastname: Ramsden
authors.forename: Luis
authors.initials: L
authors.lastname: Blanco
mesh_terms: D000595:Amino Acid Sequence; D002384:Catalysis; D004247:DNA / Q000096:biosynthesis* / Q000378:metabolism; D004253:DNA Nucleotidylexotransferase / Q000737:chemistry; D004277:DNA, Single-Stranded / Q000378:metabolism; D004259:DNA-Directed DNA Polymerase / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D006801:Humans; D008969:Molecular Sequence Data; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D017384:Sequence Deletion; D013698:Templates, Genetic
chemical_list: D004277:DNA, Single-Stranded; D004247:DNA; C407743:DNA polymerase mu; D004253:DNA Nucleotidylexotransferase; D004259:DNA-Directed DNA Polymerase