title: Binding sites for abundant nuclear factors modulate RNA polymerase I-dependent enhancer function in Saccharomyces cerevisiae.
abstract: The 190-base pair (bp) rDNA enhancer within the intergenic spacer sequences of Saccharomyces cerevisiae rRNA cistrons activates synthesis of the 35S-rRNA precursor about 20-fold in vivo (Mestel,, R., Yip, M., Holland, J. P., Wang, E., Kang, J., and Holland, M. J. (1989) Mol. Cell. Biol. 9, 1243-1254). We now report identification and analysis of transcriptional activities mediated by three cis-acting sites within a 90-bp portion of the rDNA enhancer designated the modulator region. In vivo, these sequences mediated termination of transcription by RNA polymerase I and potentiated the activity of the rDNA enhancer element. Two trans-acting factors, REB1 and REB2, bind independently to sites within the modulator region (Morrow, B. E., Johnson, S. P., and Warner, J. R. (1989) J. Biol. Chem. 264, 9061-9068). We show that REB2 is identical to the ABF1 protien. Site-directed mutagenesis of REB1 and ABF1 binding sites demonstrated uncoupling of RNA polymerase I-dependent termination from transcriptional activation in vivo. We conclude that REB1 and ABF1 are required for RNA polymerase I-dependent termination and enhancer function, respectively, Since REB1 and ABF1 proteins also regulate expression of class II genes and other nuclear functions, our results suggest further similarities between RNA polymerase I and II regulatory mechanisms. Two rDNA enhancers flanking a rDNA minigene stimulated RNA polymerase I transcription in a "multiplicative" fashion. Deletion mapping analysis showed that similar cis-acting sequences were required for enhancer function when positioned upstream or downstream from a rDNA minigene.
mesh_terms: D000595:Amino Acid Sequence; D001483:Base Sequence; D001665:Binding Sites; D004271:DNA, Fungal / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D004275:DNA, Ribosomal / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000737:chemistry / Q000378:metabolism; D004742:Enhancer Elements, Genetic; D005656:Fungal Proteins / Q000378:metabolism; D008969:Molecular Sequence Data; D009687:Nuclear Proteins / Q000378:metabolism*; D009838:Oligodeoxyribonucleotides / Q000737:chemistry; D012318:RNA Polymerase I / Q000235:genetics / Q000378:metabolism*; D012441:Saccharomyces cerevisiae / Q000235:genetics*; D029701:Saccharomyces cerevisiae Proteins; D013728:Terminator Regions, Genetic; D014157:Transcription Factors / Q000737:chemistry / Q000378:metabolism; D014158:Transcription, Genetic
chemical_list: C061886:ABF1 protein, S cerevisiae; D004271:DNA, Fungal; D004275:DNA, Ribosomal; D004268:DNA-Binding Proteins; D005656:Fungal Proteins; D009687:Nuclear Proteins; D009838:Oligodeoxyribonucleotides; C065681:REB1 protein, S cerevisiae; D029701:Saccharomyces cerevisiae Proteins; D014157:Transcription Factors; D012318:RNA Polymerase I