Human Ku antigen tightly binds and stabilizes a tetrahelical form of the Fragile X syndrome d(CGG)n expanded sequence.
Hairpin and tetrahelical structures of a d(CGG)(n) sequence in the FMR1 gene have been implicated in its expansion in fragile X syndrome. The identification of tetraplex d(CGG)(n) destabilizing proteins (Fry, M., and Loeb, L. A.(1999) J. Biol. Chem. 274, 12797-12803; Weisman-Shomer, P., Naot, Y., and Fry, M. (2000) J. Biol. Chem. 275, 2231-2238) suggested that proteins might modulate d(CGG)(n) folding and aggregation. We assayed human TK-6 lymphoblastoid cell extracts for d(CGG)(8) oligomer binding proteins. The principal binding protein was identified as Ku antigen by its partial amino acid sequence and antigenicity. The purified 88/75-kDa heterodimeric Ku bound with similar affinities (K(d) approximately 1. 8-10.2 x 10(-9) mol/liter) to double-stranded d(CGG)(8).d(CCG)(8), hairpin d(CGG)(8), single-stranded d(CII)(8), or tetraplex structures of telomeric or IgG switch region sequences. However, Ku associated more tightly with bimolecular G'2 tetraplex d(CGG)(8) (K(d) approximately 0.35 x 10(-9) mol/liter). Binding to Ku protected G'2 d(CGG)(8) against nuclease digestion and impeded its unwinding by the tetraplex destabilizing protein qTBP42. Stabilization of d(CGG)(n) tetraplex domains in FMR1 by Ku or other proteins might promote d(CGG) expansion and FMR1 silencing.
Uliel
L
L
Unit of Biochemistry, The Bruce Rappaport Faculty of Medicine, Technion, Israel Institute of Technology, Haifa 31096, Israel.
Weisman-Shomer
P
P
Oren-Jazan
H
H
Newcomb
T
T
Loeb
L A
LA
Fry
M
M
D000595:Amino Acid Sequence; D034961:Antigens, Nuclear; D001483:Base Sequence; D001665:Binding Sites; D004247:DNA / Q000737:chemistry* / Q000235:genetics*; D004265:DNA Helicases; D004268:DNA-Binding Proteins / Q000737:chemistry / Q000378:metabolism*; D005600:Fragile X Syndrome / Q000235:genetics*; D006801:Humans; D007700:Kinetics; D000072200:Ku Autoantigen; D008969:Molecular Sequence Data; D009687:Nuclear Proteins / Q000737:chemistry / Q000378:metabolism*; D009690:Nucleic Acid Conformation; D009838:Oligodeoxyribonucleotides / Q000737:chemistry / Q000378:metabolism; D014157:Transcription Factors / Q000378:metabolism; D019680:Trinucleotide Repeat Expansion
D034961:Antigens, Nuclear; D004268:DNA-Binding Proteins; D009687:Nuclear Proteins; D009838:Oligodeoxyribonucleotides; D014157:Transcription Factors; D004247:DNA; D004265:DNA Helicases; C106893:XRCC5 protein, human; C000606509:Xrcc6 protein, human; D000072200:Ku Autoantigen