Lamin A
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Lamin A is one of the intermediate filament proteins that weave together to form a shell called the nuclear lamina which lines the inner surface of the nucleus of every eukaryotic cell. Lamin A and its closely related variant, Lamin C, are both derived from the same gene by Alternative splicing of a shared pre-mRNA transcript.
The Lamin A gene is located on chromosome 1, and mutations in its sequence have been shown to cause diseases such as Progeria and Muscular Dystrophy (also see: laminopathies).
Early in mitosis, MPF phospohrylates specific serine residues in all three nuclear lamins, causing depolymerization of the lamin intermediate filaments. The phosphorylated lamin B dimers remain associated with the nuclear membrane via their isoprenyl anchor. Lamin A is targeted to the nuclear membrane by an isoprenyl group but it is cleaved shortly after arriving at the membrane. It stays associated with the membrane through protein-protein interactions of itself and other membrane associated proteins, such as LAP1. Depolymerization of the nuclear lamins leads to disintegration of the nuclear envelope. Transfection experiments demonstrate that phosphorylation of human lamin A is required for lamin depolymerization, and thus for disassembly of the nuclear envelope, which normally occurs early in mitosis.
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