Fig. 2. Proposed protein complexes spanning the NE in C. elegans, Drosophila and mammals. The nuclear lamins of several species are proposed to interact with the N-terminal regions of the SUN-domain proteins of the INM. Within the PS, the SUN-domains (or regions immediately upstream of the SUN-domains) associate with the KASH domains of ONM proteins. Within the cytoplasm, the N-terminal regions of these proteins associate with the microtubule-organizing center (MTOC), MTs, F-actin or plectin (which can directly bind to the IFs). Thus, there is a continuous protein scaffold from the nuclear lamina, through the NE, to the different cytoskeletal systems in several different species. The SUN-domain proteins are shown as dimers. SUN1 crosses the INM three times, whereas the other SUN-domain proteins cross it at least once. The two Drosophila SUN-domain proteins identified in database searches (labeled Dm-SUN in this depiction) do not contain any recognizable membrane spanning regions, although these may not represent full-length sequences.