[DNAase I hypersensitivity of the 1,5'-flanking region of the tryptophan oxygenase gene in recombinant DNA and chromatin reconstituted with it].

We have examined DNase I hypersensitive sites in the 5'-flanking region of the rat tryptophan oxygenase gene in recombinant plasmids. We have found two DNase I-hypersensitive sites in regions that map between -350 to -210 and -180 to -90 bp from the cap site. Both hypersensitive sites are found in supercoiled plasmids but not in linear or relaxed DNA molecules. The position of the hypersensitive sites of the 5'-flanking sequence of the rat tryptophan oxygenase gene in recombinant plasmids correlate with the chromatin sites first determined by Becker et al. The hypersensitive regions in the recombinant plasmids include the DNase I-hypersensitive sites in chromatin but extend somewhat upstream and downstream from these. Computer analysis of the 5'-flanking DNA region of the gene suggests that the DNA fragment spanning nucleotides -231 to -207 forms a potential hairpin loop with 15 unpaired bases. Chromatin reconstitution with histones on supercoiled plasmids carrying the 5'-flanking region of the rat tryptophan oxygenase gene suppresses both in vitro DNase I-hypersensitive sites. We have also shown that the DNA region containing the supercoil-dependent DNase I-hypersensitive site in the position between -350 and -210 bp from the cap site may form nucleosomes after reconstitution with histones.