Isolation of rat testis histone TH2B-x, and interaction of TH2B-x antiserum with histones and mononucleosomes.

A method is reported for the isolation of histone TH2B-x from rat testis by affinity chromatography on an agarose-p-chloromercurianilino column. This purified TH2B-x was used to raise antibodies in the rabbit, and the antiserum was assayed by an enzyme-linked double-antibody procedure. At low concentration the antiserum cross-reacts with histone H2B and with histones TH1-x + H1 to the extent of 11-14% of the interaction with TH2B-x. Antiserum preincubated in three successive H2B-coated tubes still retains 80-89% of the original anti-TH2B-x activity when assayed subsequently in TH2B-x-coated tubes, but cross-reaction with H2B is practically zero. The anti-TH2B-x antibodies also interact with tubes coated with mononucleosomes isolated from nuclei of seminiferous epithelial cells (SEC) of rat testis, but the interaction with mononucleosomes from rat liver nuclei is almost zero. The data suggest that in nucleosomes some of the antigenic determinants which are unique to TH2B-x are accessible, while those determinants which are common to H2B and TH2B-x are not accessible for interaction with antibodies. Competition by mononucleosomes, both from rat testis SEC and rat liver (to a lesser degree), in solution is detected by the reduction of binding of enzyme-labeled IgG to TH2B-x-coated tubes. However, an attempted competition by histones TH2B-x or H2B in solution resulted in an increase in the binding of the enzyme-labeled IgG to the mononucleosome-coated tubes. The interpretation of this type of competition assay is complicated by possible interaction of added histones with the coating mononucleosomes, followed by binding of antibodies to the histones. This TH2B-x antibody should be useful in studying changes in structure and function of chromatin during spermatogenesis and in the isolation of TH2B-x mRNA.