In eukaryotic cells, the nuclear envelope consists
of inner and outer membranes which define the border between the
nucleus and cytoplasm.
The inner and outer nuclear membranes are joined by large, supramolecular
assemblies called nuclear pore complexes through which various
molecules pass into and out of the nucleus. The inner membrane
is lined by a filamentous meshwork called the nuclear lamina made
up of proteins called lamins. The attachment of the lamins to the
inner nuclear membrane appears to occur through their association
with 4 related integral membrane proteins called Lamin Associated
Polypeptides (LAPs). LAP 1A, 1B & 1C share a high degree of
sequence homology while LAP 2 is distinct from the others.
LAP 1A & B bind lamins A, C and B1, while LAP 2 binds lamin
B1 only.
In addition to lamin binding, LAP 2 has been shown to bind to chromosomes.
Phosphorylation of LAP 2 during mitosis inhibits binding to both
lamins and chromosomes suggesting that LAP 2 plays an important
role in nuclear envelope re-assembly.
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