The mammalian dihydrofolate reductase (DHFR) gene promoters contain several conserved sequence elements which bind protein, and yet there are other conserved DNA sequences that do not footprint. We report here that mutation of one of these conserved non-footprinting regions increases transcription from this promoter both in vitro and in vivo. We show that this conserved region is flanked by sites hypersensitive to cleavage by methidiumpropyl-EDTA-Fe(II). Furthermore, multimers of a double-stranded oligonucleotide comprised of this region display faster migration through polyacrylamide than control DNA. The difference in mobility is not the result of bending, nor does the primary sequence contain features that would predict altered mobility. We propose that this 'Structural Control Element' is rigid and down-regulates transcription by inhibiting interactions between proteins binding adjacent to this region.
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