Characterization of the 130-bp repeat enhancer element of the rat ribosomal gene: functional interaction with transcription factor E 1BF

Abstract

The 130-bp repetitive element ( RE) of the rat rDNA (ribosomal RNA-encoding gene) intergenic spacer stimulated the synthesis of rRNA four- to sixfold, in comparison with that of the promoter alone, both in vivo and in vitro, when ligated to the rat rDNA promoter. The addition of increasing amounts of highly purified E 1BF (enhancer-1 binding factor), which binds to the rat rDNA promoter and an upstream nonrepetitive enhancer element [Zhang and Jacob, Mol. Cell. Biol. 10 (1990) 5177–5186], to an in vitro transcription system resulted in enhancement of rDNA transcription from the recombinant plasmids containing the promoter or promoter- RE. However, E 1BF-mediated stimulation of transcription under the influence of the RE continued at higher concentrations of E 1BF than did the control transcription from the promoter alone. The binding affinity of E 1BF for the RE was comparable to its affinity for the nonrepetitive far upstream enhancer element previously characterized in our laboratory. The sequences protected by E 1BF in the RE differed from those protected by UBF (upstream control element-binding factor), a well characterized pol I transcription factor. These data suggest that E 1BF belongs to a class of transcription factors which interact with the promoter and spacer cis-acting RE to modulate rDNA transcription.