Subcellular localization and protein-protein interaction regions of Ku proteins

The Ku protein is a complex of Ku70 and Ku80 subunits and is capable of bin ding promoters in a sequence-specific manner, although it remains unclear w hether Ku is involved in transcriptional regulation. We examined the subcel lular localization and determined the interaction regions of Ku. Our result s indicate that heterodimers of Ku70 and Ku80 are localized in the nucleus, and that the stretches from amino acid (aa) 378 to 482 of Ku70 and from aa 374 to 502 of Ku80 are necessary for heterodimerization. These interaction regions do not contain any previously recognized protein-protein interacti on motifs. To determine whether Ku contains a potential transcriptional act ivation domain, we examined N- and C-terminal deletion mutants of Ku70 and Ku80 for their ability to activate transcription in the GAL4-based one-hybr id system. We found that the whole Ku protein had no transcriptional activi ty, although the N-terminal peptide fragment of Ku70 was capable of activat ing transcription of the HIS3 and lacZ reporter genes in yeast cells. (C) 1 998 Academic Press.