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Upstream binding factor stabilizes Rib 1, the TATA-binding-protein-containing Xenopus laevis RNA polymerase I
M Bodeker1, C Cairns, B McStay
1Biomedical Research Centre, University of Dundee, Ninewells Hospital and Medical School, Scotland.
Abstract:
Initiation of RNA polymerase I transcription in Xenopus laevis requires Rib 1 and upstream binding factor (UBF). UBF and Rib 1 combine to form a stable transcription complex on the Xenopus ribosomal gene promoter. Here we show that Rib 1 comprises TATA-binding protein (TBP) and TBP-associated factor components. Thus, Rib 1 is the Xenopus equivalent of mammalian SL 1. In contrast to SL 1, Rib 1 is an unstable complex that readily dissociates into TBP and associated components. We identify a novel function for UBF in stabilizing Rib 1 by multiple protein interactions. This stabilization occurs in solution in a DNA-independent manner. These results may partially explain the difference in UBF requirement between Xenopus and mammalian systems.