LAMIN PROTEINS FORM AN INTERNAL NUCLEOSKELETON AS WELL AS A PERIPHERAL LAMINA IN HUMAN-CELLS

The nuclear lamina forms a protein mesh that underlies the nuclear mem brane, In most mammalian cells it contains the intermediate filament p roteins, lamins A, B and C. As their name indicates, lamins are genera lly thought to be confined to the nuclear periphery, We now show that they also form part of a diffuse skeleton that ramifies throughout the interior of the nucleus, Unlike their peripheral counterparts, these internal lamins are buried in dense chromatin and so are inaccessible to antibodies, but accessibility can be increased by removing chromati n, Knobs and nodes on an internal skeleton can then be immunolabelled using fluorescein- or gold-conjugated anti-lamin A antibodies, These r esults suggest that the lamins are misnamed as they are also found int ernally.