Purification and immunocytolocalization of protein phi 0 from sperm cells of the echinoderm Holothuria tubulosa.

Histones in chromatin from germ cells of the echinoderm Holothuria tubulosa are retained throughout spermatogenesis. However, some alterations occur in the histone complement of the mature sperm, including the presence of a germ-line-specific H1 subcomponent unusually rich in arginine, and the appearance of a basic component termed phi 0. Histones from ripe sperm have been extracted in a preparative scale to allow for isolation and purification of protein phi 0. Polyclonal antibodies against phi 0 have been produced and purified by affinity chromatography. The specificity of the antibodies to phi 0 has been assessed by enzyme-linked immunosorbent assays, competition experiments, and Western immunoblotting analysis. No cross-reactivity of the antibodies with the remainder histone fractions has been observed. Immunocytolocalization of protein phi 0 by immunogold labeling has revealed that this protein is essentially confined to chromatin from ripe sperm, whereas it is wholly absent from less advanced germ cell types. From these observations, together with biochemical studies previously reported, it is inferred that protein phi 0 may well be instrumental in the known chromatin transitions occurring in this organism during germ cell development.