NUCLEAR PROTEINS (Lamins)

An important part of the cell nucleus is formed by nuclear lamina.

Nuclear lamins form a network of filaments at the nucleoplasmic site of the nuclear membrane. Two main subtypes of nuclear lamins can be distinguished, i.e. A-type lamins and B-type lamins. The A-type lamins comprise a set of three proteins arising from the same gene by alternative splicing, i.e. lamin A, lamin C and lamin Adel10, while the B-type lamins include two proteins arising from two distinct genes, i.e. lamin B1 and lamin B2.

The nuclear lamins comprise a unique subclass of the intermediate filament protein family. They share a molecular domain organisation with the other intermediate filament proteins in that they are fibrous molecules that have an aminoterminal globular head, a central rod of a-helices and a carboxyterminal globular domain.

Many biochemical and molecular features of lamins have been studied, but their functions remain still largely undetermined. One of the functions ascribed to the lamina is the maintenance of the structural integrity of the nucleus.

Besides interactions with the nuclear membrane and other intermediate filaments, lamins interact with the nuclear chromatin. Eukaryotic chromatin is organised into loops, which are attached to the nuclear matrix. This organisation is thought to contribute to compaction of the chromatin and regulation of gene expression. Lamins, as part of the nuclear matrix, may be involved in these processes since chromatin binding sites have been detected in both A- and B-type lamins. For more and specific information see references 1-12.