YEAST TBP CAN REPLACE ITS HUMAN HOMOLOG IN THE RNA-POLYMERASE I-SPECIFIC MULTISUBUNIT FACTOR SL1

Basic mechanisms of transcription initiation are conserved fr om yeast to man. However, in contrast to genes transcribed hb RNA polymerases II and III, ribosomal gene transcription by RNA polymerase I (Pol I) i s species-specific. Promoter selectivity is mediated by SL1/TIF-IB, a multiprotein complex containing the TATA-binding protein (TBP) and TBP -associated factors (TAFs) which bind to DNA and nucleate the assembly of initiation complexes. Using a human cell line that expresses epito pe-tagged yeast TBP, we have isolated a chimeric complex consisting of yeast TBP and human TAFs which faithfully promotes human rDNA transcr iption in vitro. This result argues that specific interactions between TBP and Pol I-specific TAFs have been evolutionarily conserved betwee n distant species. In addition, this finding also underscores the impo rtance of TAFs in determining promoter selectivity of Pol I.