title: Ku is a general inhibitor of DNA-protein complex formation and transcription.
abstract: Ku is a ubiquitous and abundant DNA binding protein. Recently, it has been shown that Ku plays a crucial role in double stranded-DNA (dsDNA) break repair such as occurs during the V(D)J recombination of Ig genes. Ku has also been found to provide DNA binding activity to the catalytic domain of DNA-PK which is known to phosphorylate several transcription factors, suggesting that Ku is a multifunctional protein that participates as a component of several functional DNA-protein complexes. Here, we examined the interaction of Ku with several DNA binding proteins. Firstly, the DNA binding interaction between Ku and well-characterized transcription factors (OTF-1, Sp-1, AP-1) was analysed by EMSA. Although sequence non-specific, Ku was strongly competitive with these sequence specific transcription factors on compatible DNA elements, displacing them because of its high affinity association with DNA ends. Secondly, to determine whether this competitive effect was functionally relevant, we tested Ku in an in vitro transcription system with the adenovirus major late promoter. We found that Ku inhibited transcription from linear, but not from circular template DNA. These results suggest that Ku inhibits transcription when it is able to bind to template DNA and that the inhibition is the result of Ku displacing specific transcription factors from DNA.
authors.affiliation: Department of Microbiology, University of Texas Southwestern Medical Center, Dallas 75235, USA.
authors.forename: M
authors.initials: M
authors.lastname: Ono
authors.forename: P W
authors.initials: PW
authors.lastname: Tucker
authors.forename: J D
authors.initials: JD
authors.lastname: Capra
mesh_terms: D034961:Antigens, Nuclear; D001324:Autoantigens / Q000235:genetics / Q000378:metabolism / Q000494:pharmacology; D001667:Binding, Competitive / Q000187:drug effects / Q000235:genetics; D004247:DNA / Q000037:antagonists & inhibitors*; D004265:DNA Helicases; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism / Q000494:pharmacology*; D051863:Host Cell Factor C1; D006801:Humans; D000072200:Ku Autoantigen; D009687:Nuclear Proteins / Q000235:genetics / Q000378:metabolism / Q000494:pharmacology*; D050811:Octamer Transcription Factor-1; D011485:Protein Binding / Q000187:drug effects / Q000235:genetics; D011994:Recombinant Proteins / Q000378:metabolism / Q000494:pharmacology; D018808:Transcription Factor AP-1 / Q000037:antagonists & inhibitors / Q000187:drug effects / Q000378:metabolism; D014157:Transcription Factors / Q000378:metabolism; D014158:Transcription, Genetic / Q000187:drug effects*
chemical_list: D034961:Antigens, Nuclear; D001324:Autoantigens; D004268:DNA-Binding Proteins; C497692:HCFC1 protein, human; D051863:Host Cell Factor C1; D009687:Nuclear Proteins; D050811:Octamer Transcription Factor-1; C494165:POU2F1 protein, human; D011994:Recombinant Proteins; D018808:Transcription Factor AP-1; D014157:Transcription Factors; D004247:DNA; D004265:DNA Helicases; C106893:XRCC5 protein, human; C000606509:Xrcc6 protein, human; D000072200:Ku Autoantigen