Antisera Directed against Anti-Histone H4 Antibodies Recognize Linker Histones: NOVEL IMMUNOLOGICAL PROBES TO DETECT HISTONE INTERACTIONS

Abstract

We introduce a novel immunological approach to detect structural interactions between chromosomal proteins. Antigenically pure core histone H4 was prepared from chicken erythrocytes and used to produce anti-histone H4 antisera. IgG fractions were isolated from purified anti-H4 antibodies and used as antigens to produce "second generation" antisera. Epitopes cross-reacting with the second generation antisera were then identified within chromosomal proteins. These epitopes were presumed to mimic the complementary molecular surface of the original anti-H4 antibodies, and thus proteins containing these epitopes were putatively identified as specific ligands of H4 in chromatin. Surprisingly, we found this immunoreactivity was predominantly directed against H1 compared with H5 from chicken erythrocytes. Further, the immunoreactive epitopes were located within the C-terminal tail domain of the linker histones. These results suggest similar complementary interactions occur between H4 and the C-terminal tail domain of H1s in native chromatin. This could occur either within a single nucleosome as suggested by a previous report (Banères, J.-L., Essalouh, L., Jariel-Encontre, I., Mesnier, D., Garrod, S., and Parello, J. (1994) J. Mol. Biol., 243, 48-59) or between neighboring nucleosomes within the condensed chromatin fiber. The implications of these results with regard to the structure of the chromatin fiber and the future utility of this technique are discussed.