Figure 2. Hypothetical model of nuclear envelope organization in the pericentrosomal region in Dictyostelium. In both nuclear membranes (black line) Sun1 is involved in linkage of the centrosome to an NE81-based nuclear lamina. On the centrosomal side, the centrosomal corona protein CP148 is directly or indirectly associated with Sun1, on the nuclear side Sun1 is directly or indirectly bound to NE81. Centromere proteins are also associated with Sun1 and mediate clustering of centromeres in the pericentrosomal region. The tight linkage between the cytosolic centrosome and the centromere cluster and nuclear lamina could be mediated by a self-interaction between SUN-domains or by an unknown protein within the perinuclear space. At the outer nuclear membrane both the kinesin Kif9 and Sun1-associated dynein/dynactin bind to microtubules and help to hold the centrosome close to the nucleus.