An Mr 51,000 protein of mammalian spermatogenic cells that is common to the whole XY body and centromeric heterochromatin of autosomes.

During mammalian male meiotic prophase the sex chromosomes form a structure called the XY body or sex vesicle. This structure is characterized by differential condensation of chromatin and transcriptional inactivity. The reasons and mechanisms for the allocyclic behaviour of sex chromosomes with respect to autosomes are largely unknown. In order to gain insight into the process of XY-body formation we are involved in the characterization of proteins associated with meiotic sex chromosomes by immunological approaches. Here we report on the identification of an Mr 51,000 protein (p51) that is homogeneously distributed in the XY body of rodents as shown by immunocytochemistry with the novel monoclonal antibody 4EC. Interestingly, in germ line cells the antibody also labelled the centromeric heterochromatin of autosomes. We speculate that p51 may be a component of the mechanisms that lead to wide chromosome regions becoming inaccessible for transcription and/or recombination events.