DNA END-INDEPENDENT ACTIVATION OF DNA-PK MEDIATED VIA ASSOCIATION WITH THE DNA-BINDING PROTEIN C1D

DNA-dependent protein kinase (DNA-PK), which is involved in DNA double -strand break repair and V(D)J recombination, is comprised of a DNA-ta rgeting component termed Ru and an similar to 465-kD catalytic subunit , DNA-PKcs. Although DNA-PK phosphorylates proteins in the presence of DSBs or other discontinuities in the DNA double helix in vitro, the p ossibility exists that it is also activated in other circumstances via its association with additional proteins. Here, through use of the ye ast two-hybrid screen, we discover that the recently identified high a ffinity DNA binding protein CID interacts with the putative leucine zi pper region of DNA-PKcs. Furthermore, we show that C1D can interact Wi th DNA-PK in mammalian cells and that C1D is a very effective DNA-PK s ubstrate in vitro. Finally, we establish that C1D directs the activati on of DNA-PK in a manner that does not require DNA termini. Therefore, these studies provide a function for C1D and suggest novel mechanisms far DNA-PK activation in vivo.