The nucleolar transcription activator UBF relieves Ku antigen-mediated repression of mouse ribosomal gene transcription.
Previously we have shown that the RNA polymerase I (Pol I)-specific transcription factor UBF stimulates transcription by both facilitating transcription complex formation and by relieving repression exerted by a negative-acting factor which competes for binding of the murine factor TIF-IB to the ribosomal gene promoter (1). We have purified and functionally characterized this repressor protein from Ehrlich ascites cells. The final preparation contained two polypeptides with molecular masses of 75 and 90 kDa, respectively. Both polypeptides interact with the rDNA promoter as revealed by UV-crosslinking experiments. The specificity of binding to the ribosomal gene promoter was demonstrated in an electrophoretic mobility shift assay and by DNase footprinting. The biochemical properties of this negative-acting factor closely resemble those of the Ku antigen, a human nuclear DNA-binding heterodimer which is the target of autoantibodies in several autoimmune diseases. Anti-Ku antibodies precipitate the repressor activity and overcome transcription inhibition. The data demonstrate that regulation of Pol I gene transcription may involve an antirepression mechanism as already documented for Pol II genes and suggest that Ku protein may be causally involved in repressor-mediated down regulation of rRNA synthesis.
German Cancer Research Center, Heidelberg.
A
A
Kuhn
V
V
Stefanovsky
I
I
Grummt
D000818:Animals; D034961:Antigens, Nuclear; D001324:Autoantigens / Q000302:isolation & purification / Q000378:metabolism*; D001483:Base Sequence; D002286:Carcinoma, Ehrlich Tumor; D004265:DNA Helicases; D004275:DNA, Ribosomal / Q000378:metabolism*; D004268:DNA-Binding Proteins / Q000037:antagonists & inhibitors / Q000302:isolation & purification / Q000378:metabolism*; D006801:Humans; D000072200:Ku Autoantigen; D051379:Mice; D008969:Molecular Sequence Data; D009687:Nuclear Proteins / Q000037:antagonists & inhibitors / Q000302:isolation & purification / Q000378:metabolism*; D035463:Pol1 Transcription Initiation Complex Proteins; D011233:Precipitin Tests; D011401:Promoter Regions, Genetic; D011485:Protein Binding; D012097:Repressor Proteins / Q000037:antagonists & inhibitors / Q000302:isolation & purification / Q000378:metabolism*; D014157:Transcription Factors / Q000378:metabolism*; D014158:Transcription, Genetic; D014407:Tumor Cells, Cultured
D034961:Antigens, Nuclear; D001324:Autoantigens; D004275:DNA, Ribosomal; D004268:DNA-Binding Proteins; D009687:Nuclear Proteins; D035463:Pol1 Transcription Initiation Complex Proteins; D012097:Repressor Proteins; D014157:Transcription Factors; C063844:transcription factor UBF; D004265:DNA Helicases; C106893:XRCC5 protein, human; C000606509:Xrcc6 protein, human; C000606510:Xrcc6 protein, mouse; D000072200:Ku Autoantigen