Immunologically specific complexes of chromosomal nonhistone proteins with deoxyribonucleic acid in chicken erythroid nuclei.

Erythroid cell-specific antisera capable of detecting chromosomal nonhistone protein-DNA complexes were obtained by injecting rabbits with dehistonized chicken reticulocyte chromatin. The specific antigenic nonhistone protein-DNA complexes were relatively inaccessible to the antiserum in isolated erythrocyte chromatin. However, isolation of chromatin from cells at earlier stages of erythropoiesis or treatment of isolated erythrocyte chromatin with polyanions or phenylhydrazine provided materials with significantly increased immunological reactivity. The altered activity was caused by changes in conformation occurring at two levels: a specific one, determined by chromosomal nonhistone proteins, and a more general one, determined by histones. Immunological examination of fractionated products obtained from limited nuclease digestion revealed the localization of the antigenic complexes in the nuclease-resistant, large fragments of erythroid chromatin. The nuclease-resistant DNA isolated from the immunologically reactive fragments migrated in gel electrophoresis as a diffuse band of between 1000 and 2000 base pairs. No preferential accumulation of globin-specifying DNA sequences could be found in this nuclease-resistant DNA. The protein fraction containing the immunologically cell-specific complexes in chicken erythrocyte chromatin was glycosylated and moderately acidic (by amino acid anaysis) with an electrophoretically determined Mr of approximately 90000.