Immunocytogenetics. VI. A nonhistone antigen is cell type-specially associated with constitutive heterochromatin and reveals condensation centers in metaphase chromosomes.

We report a nonhistone antigen to be cell type-specifically associated with constitutive heterochromatin. Human autoantibodies were used to analyze by indirect immunofluorescence the pattern of association of the antigenic protein with the heterochromatin of murine chromosomes, as well as those of other representative vertebrate species. The evolutionary stability of its cell type-specific distribution pattern suggests that this nonhistone antigen plays an important role in the structure and/or function of constitutive heterochromatin. In mitotic chromosomes, the antigen was localized to discrete granules scattered throughout the entire chromatin. These structural elements may function as condensation centers, with each granule representing an aggregation of anchoring complexes for the chromatin loops.