Assembly/disassembly of the nuclear envelope membrane. Characterization of the membrane-chromatin interaction using partially purified regulatory enzymes.
Assembly and disassembly of the nucleus at mitosis in eukaryotes involves the reversible interaction of chromatin with the nuclear membrane. Previously we have shown that this interaction is regulated by the antagonistic activities of a kinase and a phosphatase. The kinase promotes membrane release while the phosphatase stimulates binding. In this report we describe four steps in the purification of the kinase needed for release of membranes from chromatin. We also show that the release kinase and the mitotic initiation kinase, cdc2, are distinct and are separated from each other during the second purification step. Reconstitution experiments using these two kinases demonstrate that the release kinase and cdc2 kinase work in concert to cause membrane release from chromatin. In phosphorylation experiments, protein targets that are substrates for the regulatory release kinase are identified on the membranes. These phosphorylated proteins ae candidates for regulated proteins mediating membrane-chromatin interaction. Finally, we find that membrane release activity can also be extracted from membranes by high salt treatment, indicating a possible dual localization of this activity.