Defining functional domains of Ku80: DNA end binding and survival after radiation

The Ku heterodimeric protein (Ku80/Ku70) is an essential component of the d ouble-strand break DNA repair pathway in mammalian cells, We have recently defined a central region within Ku80 that is required for heterodimerizatio n with Ku70, We now identified a core region within Ku80 (amino acids 210 t o 531) that is necessary for binding of Ku to DNA ends, Interaction with Ku 70 and DNA end binding are important for Ru80 function in vivo since Ku80 m utants lacking DNA end binding activity were unable to restore radiation re sistance in Ku80 deficient fibroblast cell lines. However, Ku80 mutants wer e identified that retained DNA end binding activity but were unable to rest ore radiation survival, thus pointing to additional functional properties o f Ku80. An N-terminal deletional mutant of Ku80 was able to suppress wild t ype Ku80 function for radiation survival in several cell lines, thus demons trating dominant negative function. (C) 1999 Academic Press.