A cell free system to study reassembly of the nuclear envelope at the end of mitosis.

We described a cell free system involving total homogenates of metaphase CHO cells, which yields telophase-like assembly of nuclear envelopes around mitotic chromosomes. During formation of the nuclear envelope in vitro, the three major lamina polypeptides (lamins A, B, and C) assemble around chromosomes and become dephosphorylated, similar to their behavior in vivo during telophase. Nuclear lamina and envelope assembly apparently do not require free ATP and are strongly inhibited by gamma-S-ATP, supporting the notion that these processes are regulated by protein dephosphorylation. Immunological depletion of disassembled lamins from the initial assembly system results in strong inhibition of subsequent nuclear envelope assembly, directly demonstrating that the lamins are involved in this process.