Immunochemical study of chromatin non-histone proteins. II. Localization of immunogenic tissue-specific proteins in nuclease-hypersensitive sites of chromatin.

Localization of immunogenic tissue-specific and tissue-non-specific non-histone proteins in thymocyte chromatin has been investigated using antibodies against rat thymus and liver chromatin. After chromatin digestion by DNAase II and subsequent fractionation with 2 mM MgCl2, the Mg2+-soluble fraction interacts with both types of antibodies 5-6 times more effectively than Mg2+-insoluble chromatin. The experiments on chromatin digestion with DNAase I indicate that tissue-specific and tissue-non-specific proteins, reacting with antibodies, are released only upon hydrolysis of the first 1-3% of DNA. Further digestion with DNAase I causes no additional solubilization of these proteins. The chromatin fraction enriched in immunogenic proteins is also released upon autolytic digestion of chromatin with endogenous nuclease. The data obtained suggest that by their function tissue-specific and tissue-non-specific antigenic determinants belong to the same class of non-histone proteins localized in the chromatin sites hypersensitive to nucleases. The possible role of these proteins in regulation of the transcription is discussed.