Cloning and characterization of the ku80 promoter

The Ku80 gene encodes an 86kd protein recently identified as a DNA end binding subunit of the DNA dependent protein kinase (DNA-PK). Characterization of the promoter region of the mouse and human Ku80 genes was initiated to delineate the transcriptional elements necessary for reported cell cycle regulation. Sequence similarity between the mouse and human promoters was limited to within the first 200 nucleotides, and neither possessed recognizable TATA or CCAAT box elements. Consensus Sp1 recognition elements were, however, present in both. In addition, a near perfect palindrome of 16 base pairs was also identified, which was present 7 times as a tandem repeat within the human Ku80 promoter and once within the mouse Ku80 promoter. In a gel shift assay, this repeat binds one or more proteins within a HeLa cell nuclear extract. The major transcription start site of the human Ku80 gene is 88bp upstream of the initiation ATG. The minimal functional promoter for human Ku80 was between 200bp and 130bp upstream of the translational start site, as determined by luciferase reporter gene fusions. Within the essential 70bp exists two of the novel repeat elements and a perfect Sp1 consensus element. It is likely that basal expression of human Ku80 is regulated by the transcription factor Sp1 and may be further modulated by a novel factor binding to the 16bp repeats.