Chromatin regions, released by endogenous nucleases, are enriched in immunogenic tissue-specific proteins.

Localization of immunogenic tissue-specific proteins in chromatin regions, hypersensitive to endogenous nucleases, has been studied using rabbit antibodies against rat thymus chromatin. It is shown that the first 1-2,5% of the chromatin (calculating on DNA), released by Mg2+-, Mn2+- and Ca2+/Mg2+-dependent nuclear endonucleases are drastically enriched in tissue-specific antigenic determinants. The released chromatin fractions are found to contain a heterogeneous set of nonhistone proteins and are deficient in histones. The cleavage of nuclear DNA by endogenous acidic nuclease, independent on bivalent ions, resulted in a significantly less enrichment of the released fractions with immunogenic proteins.