Dimerization and HMG box domains 1-3 present in Xenopus UBF are sufficient for its role in transcriptional enhancement.
Transcription of Xenopus ribosomal genes by RNA polymerase I is directed by a stable transcription complex that forms on the gene promoter. This complex is comprised of the HMG box factor UBF and the TBP-containing complex Rib1. Repeated sequence elements found upstream of the ribosomal gene promoter act as RNA polymerase I-specific trans-criptional enhancers. These enhancers function by increasing the probability of a stable transcription complex forming on the adjacent promoter. UBF is required for enhancer function. This role in enhancement is distinct from that at the promoter and does not involve translocation of UBF from enhancer repeats to the promoter. Here we utilize an in vitro system to demonstrate that a combination of the dimerization domain of UBF and HMG boxes 1-3 are sufficient to specify its role in enhancement. We also demonstrate that the acidic C-terminus of UBF is primarilyresponsible for its observed interaction with Rib1. Thus, we have uncoupled the Rib1 interaction and enhancer functions of UBF and can conclude that direct interaction with Rib1 is not a prerequisite for the enhancer function of UBF.
Biomedical Research Centre, University of Dundee, Ninewells Hospital and Medical School, Dundee DD1 9SY, UK.
G J
GJ
Sullivan
B
B
McStay
D000818:Animals; D001665:Binding Sites; D004268:DNA-Binding Proteins / Q000096:biosynthesis / Q000302:isolation & purification / Q000378:metabolism / Q000502:physiology*; D019281:Dimerization; D004742:Enhancer Elements, Genetic; D006609:High Mobility Group Proteins / Q000378:metabolism / Q000502:physiology*; D016296:Mutagenesis; D035463:Pol1 Transcription Initiation Complex Proteins; D011401:Promoter Regions, Genetic; D014157:Transcription Factors / Q000096:biosynthesis / Q000302:isolation & purification / Q000378:metabolism / Q000502:physiology*; D014158:Transcription, Genetic; D014981:Xenopus; D029867:Xenopus Proteins
D004268:DNA-Binding Proteins; D006609:High Mobility Group Proteins; D035463:Pol1 Transcription Initiation Complex Proteins; C092979:Rib1 protein, Xenopus; D014157:Transcription Factors; D029867:Xenopus Proteins; C063844:transcription factor UBF