chapter  19
CAAX-dependent modifications of the
Pages 13

The important biological functions of the nuclear envelope (NE) and its associated structures include the compartmentalization of the nucleoplasm and cytoplasm, provision of a regulated, bi-directional nucleocytoplasmic transport mechanism and finally the organization of the nuclear periphery (Goldman et al., 2002). There is no doubt that minor roles for the nuclear envelope may also exist related to specific functions of individual NE proteins, for example the steroid reductase activity of the lamin B receptor (Silve et al., 1998). In order to achieve heterogeneity of interactions at the nuclear periphery a certain degree of organization is required within the nuclear envelope superstructure, which may relate to the organization of the underlying chromatin or sites of chromatin attachment to the nuclear envelope. Transcriptionally poor heterochromatin is known preferentially to occupy peripheral nuclear sites (Cremer and Cremer 2001). Moreover, chromosomes partition between the nuclear periphery and nuclear interior dependent on the gene content and level of transcriptional activity (Boyle et al., 2001). The positioning of chromatin domains is transmitted to daughter nuclei, suggesting that the epigenetic factors that influence gene activity and therefore differentiation are stereotypical between mother and daughter cells for a given cell type (Gerlich et al., 2003). This organization may be driven by the peripheral chromatin, dictated by domains within NE components, or, perhaps more likely, result from a dynamic interaction of the two.