title: Ku suppresses formation of telomeric circles and alternative telomere lengthening in Arabidopsis.
abstract: Telomeres in mammals and plants are protected by the terminal t loop structure, the formation of which parallels the first steps of intrachromatid homologous recombination (HR). Under some circumstances, cells can also utilize an HR-based mechanism (alternative lengthening of telomeres [ALT]) as a back-up pathway for telomere maintenance. We have found that the Ku70/80 heterodimer, a central nonhomologous end-joining DNA repair factor, inhibits engagement of ALT in Arabidopsis telomerase-negative cells. To further assess HR activities at telomeres, we have developed a sensitive assay for detecting extrachromosomal telomeric circles (t circles) that may arise from t loop resolution and aberrant HR. We show that Ku70/80 specifically inhibits circle formation at telomeres, but not at centromeric and rDNA repeats. Ku inactivation results in increased formation of t circles that represent approximately 4% of total telomeric DNA. However, telomeres in ku mutants are fully functional, indicating that telomerase efficiently heals ongoing terminal deletions arising from excision of the t circles.
authors.affiliation: Gregor Mendel Institute of Molecular Plant Biology, Austrian Academy of Sciences, 1030 Vienna, Austria.
authors.forename: Barbara
authors.initials: B
authors.lastname: Zellinger
authors.forename: Svetlana
authors.initials: S
authors.lastname: Akimcheva
authors.forename: Jasna
authors.initials: J
authors.lastname: Puizina
authors.forename: Martina
authors.initials: M
authors.lastname: Schirato
authors.forename: Karel
authors.initials: K
authors.lastname: Riha
mesh_terms: D017360:Arabidopsis / Q000378:metabolism*; D029681:Arabidopsis Proteins / Q000378:metabolism*; D032461:Chromosomes, Plant / Q000235:genetics; D004265:DNA Helicases / Q000378:metabolism*; D004270:DNA, Circular / Q000378:metabolism*; D004268:DNA-Binding Proteins / Q000378:metabolism*; D015180:Electrophoresis, Gel, Two-Dimensional; D009154:Mutation / Q000235:genetics; D016615:Telomere / Q000378:metabolism*
chemical_list: D029681:Arabidopsis Proteins; D004270:DNA, Circular; D004268:DNA-Binding Proteins; C463462:KU70 protein, Arabidopsis; D004265:DNA Helicases; C469228:Ku80 protein, Arabidopsis