title: Torsional stress stabilizes extended base unpairing in suppressor sites flanking immunoglobulin heavy chain enhancer.
abstract: DNA sequences surrounding the immunoglobulin heavy chain (IgH) enhancer contain negative regulatory elements which are important for the tissue specificity of the enhancer. We have shown that sequences located both 5' and 3' of the enhancer, corresponding to the negative regulatory elements, become stably and uniformly unpaired over an extended length when subjected to torsional stress. These DNA sequences are also included within matrix association regions. The ability of the sequences to assume a stably unpaired conformation was shown by reactivity with chloroacetaldehyde which is specific for unpaired DNA bases, as well as two-dimensional gel electrophoresis of topoisomers. The sequences located 3' of the enhancer induce base unpairing in the direction of the enhancer. This unpaired region progressively expands to include as much as 200 base pairs as the ionic concentration decreases or superhelical density increases. When an ATATAT motif within a negative regulatory element located 3' of the enhancer was mutated, the extensive base-unpairing property was abolished. This base-unpairing property of DNA may be important for negative regulation of gene expression and attachment to the nuclear matrix.
authors: Cancer Research Center, La Jolla Cancer Research Foundation, California 92037.
authors: T
authors: T
authors: Kohwi-Shigematsu
authors: Y
authors: Y
authors: Kohwi
mesh_terms: D000818:Animals; D001482:Base Composition; D001483:Base Sequence; D004247:DNA / Q000235:genetics / Q000302:isolation & purification; D015180:Electrophoresis, Gel, Two-Dimensional; D004742:Enhancer Elements, Genetic; D005809:Genes, Regulator; D016153:Genes, Suppressor; D007143:Immunoglobulin Heavy Chains / Q000235:genetics*; D051379:Mice; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D009690:Nucleic Acid Conformation; D010957:Plasmids; D015183:Restriction Mapping; D013314:Stress, Mechanical
chemical_list: D007143:Immunoglobulin Heavy Chains; D004247:DNA