The inner membrane of the nuclear envelope lies next to a layer of thin filaments which surrounds the nucleus except at the nuclear pores. These may also serve as stabilizing filaments. This structure is called the "nuclear lamina". It has the following structural and functional characteristics.
Consists of "intermediate filaments", 30-100 nm thick.
These intermediate filaments are polymers of lamin, ranging from 60-75 kD
A-type lamins are inside, next to nucleoplasm; B-type lamins are near the nuclear membrane (inner). They may bind to integral proteins inside that membrane.
The lamins may be involved in the functional organization of the nucleus.
They may play a role in assembly and disassembly before and after mitosis. After they are phosphorylated, this triggers the disassembly of the lamina and causes the nuclear envelope to break up into vesicles. Dephosphorylation reverses this and allows the nucleus to reform. See Alberts et al, Molecular Biology of the Cell, Garland Pub. 1994, p 567, Figure 12-18
NOTE: If antibodies to lamins are injected into cells, the nuclei cannot reform after cell division. Therefore, these lamins are vital to reassembly.
