Bleomycins are small glycopeptide cancer chemotherapeutics that give rise to 3'-modified DNA double-strand breaks (DSBs). In Saccharomyces cerevisiae, DSBs are predominantly repaired by RAD52-dependent homologous recombination (HR) with some support by Yku70/Yku80 (KU)-dependent pathways. The main DSB repair function of KU is believed to be as part of the non-homologous end-joining (NHEJ) pathway, but KU also functions in a "chromosome healing" pathway that seals DSBs by de novo telomere addition. We report here that rad52 Delta yku70 Delta double mutants are considerably more bleomycin hypersensitive than rad52 Delta lig4 Delta cells that lack the NHEJ-specific DNA ligase 4. Moreover, the telomere-specific KU mutation yku80-135i also dramatically increases rad52 Delta bleomycin hypersensitivity, almost to the level of rad52 Delta yku80 Delta. The results indicate that telomere-specific functions of KU play a more prominent role in the repair of bleomycin-induced damage than its NHEJ functions, which could have important clinical implications for bleomycin-based combination chemotherapies. (c) 2007 Elsevier Inc. All rights reserved.