High impact information on YKU70

• Saccharomyces cells suffering a single unrepairable double-strand break (DSB) exhibit a long, but transient arrest at G2/M. hdf1 cells, lacking Ku70p, fail to escape from this RAD9/RAD17-dependent checkpoint [1].
• Permanent arrest in hdf1 cells is suppressed by rad50 or mre11 deletions that retard this degradation [1].
• The effect of hdf1 results from its accelerated 5' to 3' degradation of the broken chromosome [1].
• Mlp2 physically tethers Yku70 to the nuclear periphery, thus forming a link between chromatin and the nuclear envelope [2].
• The only protein found to be involved in the peripheral localization of telomeres is Yku70/Yku80 [2].

Biological context of YKU70

• We used the yeast two-hybrid assay to show that Hdf1 interacts with Sir4, which is involved in transcriptional silencing at telomeres and HM loci [3].
• To examine whether Hdf1 is involved in illegitimate recombination, we have measured the rate of deletion mutation caused by illegitimate recombination on a plasmid in an hdf1 disruptant [4].
• The hdf1 mutation reduced the rate of deletion formation by 20-fold, while it did not affect mitotic and meiotic homologous recombinations between two heteroalleles or homologous recombination between direct repeats [4].
• Increased Exo1 or TLC1 RNA did not alter checkpoint responses or restore NHEJ proficiency, but DNA repair defects of yku70 and rad27 (fen) mutants were differentially suppressed by the two genes [5].
• We found low and comparable frequencies of aberrational events in wildtype and hdf1 mutants, and assume that in these strains most of the survivors descended from cells that were in G2 phase during irradiation and therefore able to repair breaks by homologous recombination between sister chromatids [6].

Associations of YKU70 with chemical compounds

• The human Ku protein cannot complement this temperature-sensitive phenotype. hdf2(-) strains are sensitive to bleomycin and methyl methanesulfonate, but this sensitivity is reduced in comparison with hdf1(-) strains [7].
• Ku-dependent repair is distinct from homologous recombination, because deletion of KU80 and HDF1 increased the MMS sensitivity of rad52delta [8].
• Here we show that hdf1-disrupted S. cerevisiae strains are strongly sensitive toward the radiomimetic antibiotic bleomycin [9].
• In cells competent for homologous recombination, we could not detect any sensitivity to ionizing radiation or to methyl methanesulfonate (MMS) conferred by a hdf1 deletion and indeed, the repair of DNA double-strand breaks was not impaired [10].
• Frequencies of X-ray-associated and DSB-initiated translocations were five-fold higher in yku70 mutants compared to wild type; however, frequencies of phleomycin-associated translocations were lower in the yku70 haploid mutant [11].

Regulatory relationships of YKU70

• Interestingly, an extra copy of YKU70 partially suppressed the increase in targeted integration seen in the sgs1 single mutant [12].
• However, yku70 mutations enhance the radiosensitivity of rad52 strains, which are deficient in homologous recombination [13].
• Enhanced stimulation of chromosomal translocations and sister chromatid exchanges by either HO-induced double-strand breaks or ionizing radiation in Saccharomyces cerevisiae yku70 mutants [11].

Other interactions of YKU70

• Analyses of sir4 mutants showed that Sir4 is required for deletion by illegitimate recombination and DNA end-joining in the pathway involving Hdf1 [3].
• We report that deletion of YKU70 or YKU80 suppresses mec1Delta, but not rad53Delta, lethality [14].
• In a synthetic lethality screen with YKU70, the 70-kDa subunit of the telomere-associated Yku heterodimer, we identified a new mutation in CDC13, cdc13-4, that points toward an additional regulatory function of CDC13 [15].
• Thus, Rad52 and Yku70 are the key regulators of T-DNA integration, channeling integration into either the HR or NHR pathway [16].
• The yku70 mutation caused a fourfold increase in the rate of double-strand break (DSB)-induced target integration as that seen in the sgs1 mutant [12].

Analytical, diagnostic and therapeutic context of YKU70

• Whereas this damage is repaired accurately in YKU70 backgrounds, in yku70 mutant strains terminal deletions of up to several hundred bp occur before ligation ensues [13].

References