Detection of distinct structural domains within the primary constriction using autoantibodies.

We report the immunological differentiation of structures within the primary constriction. These include the kinetochore and the connecting strand, a structure which connects sister kinetochores. The location and temporal appearance of the connecting strand antigen suggest that it could play a role in the maintenance of sister chromatid pairing. In addition, we report the identification of a novel epitope that is localized to discrete patches along the entire length of the junction between sister chromatids at metaphase (the junction patch antigen). The patches on the inner surface of the euchromatic arms can be disrupted by Colcemid treatment while those found in the primary constriction remain intact. The apparent heterogeneity of the patches suggests that they may play different roles in the regulation of sister chromatid pairing. Because of their cytological localization and possible functional role, the junction patch and connecting strand antigens have provisionally been collectively termed CLiPs (Chromatid Linking Proteins). All of these antigenic sites are shown to be distinct from centromeric heterochromatin, which can itself be immunologically differentiated from the euchromatic arms. The relationship between the antigenicity of the primary constriction and the unique manner in which chromatin is organized in this region is discussed.