Figure 8.

Binding of the Mps3 SUN domain to Mps2 C terminus tethers the SPB to the half-bridge. Mps3 (green) is an integral membrane protein localized primarily to the inner nuclear membrane with its N terminus exposed to the nucleoplasm/cytoplasm and its C terminus located in the membrane space between the inner and outer nuclear membranes (INM and ONM, respectively). Here, the SUN domain of Mps3 (yellow) can interact with the C terminus of integral membrane proteins such as Mps2 (red) to build the half-bridge (black) and anchor it to the core SPB, which is important for SPB duplication and karyogamy. Previous work showed that the N terminus of Mps2 binds to the soluble protein Bbp1 (orange), which interacts with the core SPB protein Spc29 (black; Schramm et al., 2000). It is possible that the SUN domain of Mps3 also interacts with other proteins, such as Jem1 (purple; see Discussion).