Multiple domains of the RNA polymerase I activator hUBF interact with the TATA-binding protein complex hSL1 to mediate transcription.
Recent evidence suggests that transcription initiation by all three eukaryotic RNA polymerases involves a complex of the TATA-binding protein (TBP) and multiple TBP-associated factors (TAFs). Here, we map the functional domains of the nucleolar HMG box protein hUBF, which binds to the human rRNA promoter and stimulates transcription by RNA polymerase I through cooperative interactions with a distinct TBP-TAF complex, hSL1. DNase I footprint analysis of mutant hUBF proteins and of a synthetic peptide of 84 amino acids reveals that HMG box 1 is necessary and sufficient for DNA sequence specificity, whereas other HMG boxes and the amino terminus modulate the binding efficiency. hUBF contains multiple activation domains that include the acidic carboxyl terminus and three HMG boxes. HMG boxes 3 and 4 and the acidic tail contribute significantly to an extended footprinting pattern in the presence of hSL1, suggestive of specific protein-protein interactions. Moreover, the inability of xUBF from Xenopus laevis to form an initiation complex with hSL1 can be overcome by hybrid proteins containing human HMG box 4 and the acidic carboxyl terminus. These results strongly suggest an important role of transcription activation domains of hUBF in mediating interactions with the TBP-TAF complex hSL1.
Jantzen
H M
HM
Howard Hughes Medical Institute, Department of Molecular and Cell Biology, University of California, Berkeley 94720.
Chow
A M
AM
King
D S
DS
Tjian
R
R
D000818:Animals; D001483:Base Sequence; D004247:DNA / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000378:metabolism*; D004789:Enzyme Activation; D006801:Humans; D006822:Hybrid Cells; D046911:Macromolecular Substances; D008969:Molecular Sequence Data; D010957:Plasmids; D035463:Pol1 Transcription Initiation Complex Proteins; D011401:Promoter Regions, Genetic; D011485:Protein Binding; D014176:Protein Biosynthesis; D012318:RNA Polymerase I / Q000378:metabolism*; D012335:RNA, Ribosomal / Q000235:genetics; D016385:TATA Box; D035181:TATA-Box Binding Protein; D014157:Transcription Factors / Q000378:metabolism*; D014158:Transcription, Genetic; D014982:Xenopus laevis
D004268:DNA-Binding Proteins; D046911:Macromolecular Substances; D035463:Pol1 Transcription Initiation Complex Proteins; D012335:RNA, Ribosomal; D035181:TATA-Box Binding Protein; D014157:Transcription Factors; C063844:transcription factor UBF; D004247:DNA; D012318:RNA Polymerase I