Oligomerization of the transcription termination factor TTF-I: implications for the structural organization of ribosomal transcription units.
Mammalian ribosomal genes are flanked at their 5'and 3'ends by terminator sequences which are recognized by the transcription termination factor TTF-I. The occurrence of the same binding site upstream and downstream of the gene raises the possibility that TTF-I can interact with both sequences simultaneously and thus brings the terminator in the vicinity of the gene promoter by looping out the pre-rRNA coding sequence. To test this model, we have examined the ability of TTF-I to oligomerize and found that both full-length and N-terminally truncated versions of TTF-I form stable oligomeric structures. At least two domains of TTF-I located within the 184 N-terminal and 445 C-terminal amino acids, respectively, mediate the self-association of several TTF-I molecules. In support of the looping model, TTF-I is capable of linking two separate DNA fragments via binding to the target sites. This result indicates that in addition to its function in transcription termination, TTF-I may serve a role in the structural organization of the ribosomal genes which may be important for maintaining the high loading density of RNA polymerase I on active rRNA genes.
Sander
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Division of Molecular Biology of the Cell II, German Cancer Research Center, D-69120 Heidelberg, Germany.
Grummt
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D000818:Animals; D001665:Binding Sites; D002850:Chromatography, Gel; D003001:Cloning, Molecular; D004268:DNA-Binding Proteins / Q000737:chemistry* / Q000302:isolation & purification / Q000378:metabolism*; D005982:Glutathione Transferase; D046911:Macromolecular Substances; D008322:Mammals; D016297:Mutagenesis, Site-Directed; D010454:Peptide Termination Factors / Q000737:chemistry / Q000378:metabolism; D011993:Recombinant Fusion Proteins / Q000096:biosynthesis / Q000737:chemistry / Q000302:isolation & purification; D012270:Ribosomes / Q000378:metabolism*; D017384:Sequence Deletion; D016324:Sequence Tagged Sites; D018411:Spodoptera; D014158:Transcription, Genetic; D014162:Transfection
D004268:DNA-Binding Proteins; D046911:Macromolecular Substances; D010454:Peptide Termination Factors; D011993:Recombinant Fusion Proteins; D005982:Glutathione Transferase