Localization of a multi-catalytic, high-molecular mass proteinase in the nuclei of muscle cells.

A multi-catalytic protease in muscle cells was uniquely localized to the nucleus of muscle cells, both in cell culture and in sections of muscle tissue. Although no specific substructure of the nucleus could be identified as the site of the enzyme by immunocytochemical techniques, the enzyme was nevertheless present in all muscle cell nuclei. It appears that MCP is a useful marker for nuclei found specifically in muscle tissue.