The lamina-associated
polypeptide (LAP) 2 family comprises up to six alternatively spliced
proteins in mammalian cells and three
isoforms in Xenopus.
LAP2beta is a type II integral
protein of the inner nuclear membrane, which binds to
lamin B and the chromosomal
protein BAF, and may link the nuclear membrane to the underlying lamina and provide docking sites for
chromatin.
LAP2alpha shares only the N-terminus with the other
isoforms and contains a unique C-terminus. It is a nonmembrane
protein associated with the nucleoskeleton and may help to organize higher order
chromatin structure by interacting with A-
lamins and chromosomes. Recent studies using
mutant proteins have just begun to unravel functions of LAP2
isoforms during postmitotic nuclear reassembly.
LAP2alpha associates with chromosomes via an alpha-specific domain at early stages of assembly, possibly providing a structural framework for chromosome reorganization. The subsequent interaction of both
LAP2alpha and
LAP2beta with the chromosomal BAF may stabilize
chromatin structure and target membranes to the chromosomes. At later stages LAP2 may regulate the assembly of
lamins. LAP2
isoforms have been found to share a homologous approximately 40
amino acid long region, the LEM domain, with nuclear membrane
proteins MAN1 and
emerin, which has been implicated in
Emery-Dreifuss muscular dystrophy.