title: Association of terminal deoxynucleotidyl transferase with Ku.
abstract: Terminal deoxynucleotidyl transferase (TdT) catalyzes the addition of nucleotides at the junctions of rearranging Ig and T cell receptor gene segments, thereby generating antigen receptor diversity. Ku is a heterodimeric protein composed of 70- and 86-kDa subunits that binds DNA ends and is required for V(D)J recombination and DNA double-strand break (DSB) repair. We provide evidence for a direct interaction between TdT and Ku proteins. Studies with a baculovirus expression system show that TdT can interact specifically with each of the Ku subunits and with the heterodimer. The interaction between Ku and TdT is also observed in pre-T cells with endogenously expressed proteins. The protein-protein interaction is DNA independent and occurs at physiological salt concentrations. Deletion mutagenesis experiments reveal that the N-terminal region of TdT (131 amino acids) is essential for interaction with the Ku heterodimer. This region, although not important for TdT polymerization activity, contains a BRCA1 C-terminal domain that has been shown to mediate interactions of proteins involved in DNA repair. The induction of DSBs in Cos-7 cells transfected with a human TdT expression construct resulted in the appearance of discrete nuclear foci in which TdT and Ku colocalize. The physical association of TdT with Ku suggests a possible mechanism by which TdT is recruited to the sites of DSBs such as V(D)J recombination intermediates.
authors.affiliation: University of North Carolina Lineberger Comprehensive Cancer Center, Chapel Hill, NC 27599, USA.
authors.forename: K N
authors.initials: KN
authors.lastname: Mahajan
authors.forename: L
authors.initials: L
authors.lastname: Gangi-Peterson
authors.forename: D H
authors.initials: DH
authors.lastname: Sorscher
authors.forename: J
authors.initials: J
authors.lastname: Wang
authors.forename: K N
authors.initials: KN
authors.lastname: Gathy
authors.forename: N P
authors.initials: NP
authors.lastname: Mahajan
authors.forename: W H
authors.initials: WH
authors.lastname: Reeves
authors.forename: B S
authors.initials: BS
authors.lastname: Mitchell
mesh_terms: D000818:Animals; D034961:Antigens, Nuclear; D001665:Binding Sites; D019556:COS Cells; D002460:Cell Line; D004247:DNA / Q000378:metabolism; D004249:DNA Damage; D004265:DNA Helicases; D004253:DNA Nucleotidylexotransferase / Q000235:genetics / Q000378:metabolism*; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D000072200:Ku Autoantigen; D009687:Nuclear Proteins / Q000235:genetics / Q000378:metabolism*; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D018411:Spodoptera / Q000166:cytology; D014407:Tumor Cells, Cultured
chemical_list: D034961:Antigens, Nuclear; D004268:DNA-Binding Proteins; D009687:Nuclear Proteins; D011993:Recombinant Fusion Proteins; D004247:DNA; D004253:DNA Nucleotidylexotransferase; D004265:DNA Helicases; C106893:XRCC5 protein, human; C000606509:Xrcc6 protein, human; D000072200:Ku Autoantigen