Distinct faces of the Ku heterodimer mediate DNA repair and telomeric functions.
The Ku heterodimer, comprised of Ku70 and Ku80 subunits, is a conserved complex involved in nonhomologous end-joining (NHEJ). However, it also functions in maintenance of telomeres, chromosome termini normally resistant to end-joining events. To elucidate the spatial organization of these functions, we rationally guided Ku mutagenesis in yeast with real-valued evolutionary trace (rvET). This revealed two ancestrally related alpha-helices: one on the Ku70 surface that is required in yeast for NHEJ, and a second on the Ku80 surface that is required in yeast for telomeric heterochromatin formation. When bound to a DNA end, the surface containing the NHEJ-specific Ku70 helix is oriented toward the DNA terminus, whereas the surface containing the telomeric function-specific Ku80 helix faces inward, toward telomeric chromatin, when bound to a telomere. We propose a 'two-face' model for Ku and that divergent evolution of these faces allowed Ku's dual role in NHEJ and telomere maintenance.
Ribes-Zamora
Albert
A
Department of Pediatrics, Hematology/Oncology Section, Baylor College of Medicine, One Baylor Plaza, BCM225, Houston, Texas 77030-3411, USA.
Mihalek
Ivana
I
Lichtarge
Olivier
O
Bertuch
Alison A
AA
D000595:Amino Acid Sequence; D034961:Antigens, Nuclear / Q000737:chemistry* / Q000378:metabolism*; D016000:Cluster Analysis; D004260:DNA Repair; D004268:DNA-Binding Proteins / Q000737:chemistry* / Q000378:metabolism*; D019281:Dimerization; D006801:Humans; D000072200:Ku Autoantigen; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009154:Mutation / Q000235:genetics; D011485:Protein Binding; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D011995:Recombination, Genetic / Q000235:genetics; D012441:Saccharomyces cerevisiae / Q000166:cytology / Q000378:metabolism*; D038281:Silent Information Regulator Proteins, Saccharomyces cerevisiae / Q000378:metabolism; D013329:Structure-Activity Relationship; D016615:Telomere / Q000378:metabolism*
D034961:Antigens, Nuclear; D004268:DNA-Binding Proteins; C061573:SIR4 protein, S cerevisiae; D038281:Silent Information Regulator Proteins, Saccharomyces cerevisiae; C000606509:Xrcc6 protein, human; D000072200:Ku Autoantigen