Maturation of nuclear lamin A involves a specific carboxy-terminal trimming, which removes the polyisoprenylation site from the precursor; implications for the structure of the nuclear lamina.

Lamin A, a nuclear lamina protein of differentiated cells, is synthesized as a precursor of the mature molecule. Protein sequencing of the carboxy-terminal 14 kDa fragment shows a lack of the last 18 residues predicted by cDNA sequencing. The carboxy-terminal proteolytic maturation explains previous biochemical results including the loss of the polyisoprenylation site now located to the CXXM motif at the end of the chain. This view and earlier results on lamin B predict multiple post-translational modifications shared by lamins A and B. While retained by lamin B, which is present in all cells, they are lost by maturation from lamin A, which probably acts only as an additional lamina constituent in differentiated cells.