[Immunochemical study of non-histone proteins in chromatin regions distinguished by sensitivity to nucleases].

Immunization of rabbits with rat thymus chromatin induces synthesis of antibodies against tissue specific antigenic determinants preferentially. At the same time antisera against liver chromatin interact both with homologous and thymus chromatin. Antiliver IgG preincubated with thymus chromatin react with homologous chromatin only, and hence they contain antibodies against both tissue specific and tissue nonspecific antigenic determinants. We studied localization of reactive tissue specific and tissue nonspecific proteins in thymus chromatin using antibodies against liver and thymus chromatin. After chromatin digestion with DNAase II and subsequent fractionation with 2 mM MgCl2, Mg2+-soluble fraction interacts with antibodies 5-6 times more effectively than Mg2+-insoluble chromatin. Experiments on chromatin digestion with DNAase I indicate that tissue specific and tissue nonspecific proteins are released during hydrolysis of the first 1-3% DNA only. Subsequent digestion with DNAase I does not lead to additional solubilization of these proteins. The data obtained show that the investigated tissue specific and tissue nonspecific antigenic determinants belong to functionally similar non-histone proteins, which are localized in the chromatin regions hypersensitive to DNAase I. The possible role of these proteins in the regulation of transcription is discussed.