Glucocorticoid-Receptor Complex Binds to Nonhistone Protein and DNA in Rat Liver Chromatin1

Abstract

The glucocorticoid (cortisol)-receptor complex from rat liver cytoplasm was interacted with various chromatin preparations from rat tissues in a cell-free system. The complex showed the highest extent of binding to liver chromatin among liver, thymus, prostate, and uterus chromatins but the same extent of binding to DNAs isolated from the four tissues. Chemical analyses of these chromatins suggest that some qualitative differences in the nonhistone protein components may be responsible for the different extents of binding. The complex also showed two-fold higher extents of binding to the aggregate chromatin fraction and de-histonized chromatin than to the intact liver chromatin, but half or lower extents of binding to the soluble chromatin fraction, deproteinized chromatin, etc. These various extents of binding could be related to the nonhistone protein content of each chromatin fraction, but not to the histone content. This was further supported by similar binding experiments using various chromatin preparations treated with DNases or proteases. The cytoplasmic cortisol-receptor complex had the same sedimentation coefficient of about 4S in the absence and presence of 0.3 m NaCl. An apparently identical 4S complex was released from the complex-bound chromatin or nuclei by 0.3 m NaCl extraction or by DNase or protease digestion. A 6-7S complex existed only in the salt extract and could again bind to DNA in 0.3 m NaCl to a much larger extent than the 4S complex in the extract. This 6-7S complex may be a combined form of the 4S complex and its acceptor nonhistone protein molecule. These results also support the conclusion that the cortisol-receptor complex binds to some nonhistone protein components and DNA regions in the liver chromatin. These binding characteristics may imply the recognition and activation of the selected gene for the steroid-induced transcription.