Cytosol induces apparent selectivity of glucocorticoid receptor binding to nucleic acids of different secondary structure.

Unpurified rat liver glucocorticoid-receptor complexes within cytosol show a distinct binding preference for double-stranded DNA over single-stranded DNA; the binding to Escherichia coli rRNA is negligible. Extensive purification of the receptor abolishes its ability to distinguish among DNAs of different secondary structure and the affinity of the purified receptor toward RNA is greatly enhanced, reaching 30-50% of that of DNA. The purification effect is reversible: after cytosol addition to purified receptor preparation the binding preference restores. NaCl does not mimic the effect of cytosol. The flow-through fraction of a phosphocellulose column retains the ability of crude cytosol to produce selective decrease in the receptor binding to single-stranded DNA. This effect may also be observed by using two types of DNA-cellulose bearing double-stranded or denatured DNA, pretreated with crude cytosol. Additionally, pretreatment of immobilized DNA with even low cytosol concentrations has been shown to markedly enhance receptor binding, although this enhancement was lacking specificity with respect to DNA secondary structure. The nature of cytosolic active principle and some possible regulatory implications are discussed.