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 stru cture called the XY body or sex vesicle. This structure is characteriz ed by differential condensation of chromatin and transcriptional inact ivity. 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 chromoso mes 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 mon oclonal antibody 4EC. Interestingly, in germ line cells the antibody a lso labelled the centromeric heterochromatin of autosomes. We speculat e that p51 may be a component of the mechanisms that lead to wide chro mosome regions becoming inaccessible for transcription and/or recombin ation events.