Abstract
Previous studies from this laboratory have characterized a 174 by enhancer element which is located 2kb upstream of the initiation site. Half of the enhancer action is controlled by a 37 by element at the 3′ end of the 174 by region. We now report that a 43 by adjacent domain which is located upstream of the 37 by element constitutes an additional motif of the rDNA enhancer. When the plasmid consisting of the 43 by DNA upstream of the rDNA core promoter was transcribed in a fractionated rat tumor cell extract (fraction DE-B), transcription of rDNA was augmented 4 fold. Electrophoretic mobility shift and DNAase I footprinting analyses showed that the purified 37 by enhancer (E1)-binding protein, (E1BF) not only interacted with the enhancer motif El but also interacted with the neighbouring 43 by enhancer domain E2. The specificity of the binding was demonstrated by competition with unlabeled 37 by and 43 by fragment and lack of competition with nonspecific DNAs in the mobility shift assay. These studies have shown that a single pol I transcription factor can bind to multiple enhancer domains with no significant sequence homologies and such multiple interactions may result in maximal transcription of ribosomal gene from the core promoter.
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Jacob, S.T., Zhang, J., Garg, L.C. et al. Multiple functional enhancer motifs of rat ribosomal gene. Mol Cell Biochem 104, 155–162 (1991). https://doi.org/10.1007/BF00229815
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DOI: https://doi.org/10.1007/BF00229815