SUN-1 and ZYG-12, mediators of centrosome-nucleus attachment, are a functional SUN/KASH pair in Caenorhabditis elegans

• Published in: Molecular biology of the cell 2009-11, Vol.20 (21), p.4586-4595
• Main Authors: Minn, I L, Rolls, Melissa M, Hanna-Rose, Wendy, Malone, Christian J
• Format: Article
• Language: English
• Subjects: Amino Acid Sequence; Animals; Caenorhabditis elegans - genetics; Caenorhabditis elegans - metabolism; Caenorhabditis elegans Proteins - genetics; Caenorhabditis elegans Proteins - metabolism; Cell Cycle Proteins - genetics; Cell Cycle Proteins - metabolism; Cell Nucleus - metabolism; Centrosome - metabolism; HeLa Cells; Humans; Molecular Sequence Data; Nuclear Envelope - metabolism; Protein Structure, Tertiary; Receptors, Cytoplasmic and Nuclear - genetics; Receptors, Cytoplasmic and Nuclear - metabolism; Recombinant Fusion Proteins - genetics; Recombinant Fusion Proteins - metabolism; Two-Hybrid System Techniques
• ISSN: 1059-1524; 1939-4586
• DOI: 10.1091/mbc.e08-10-1034

Klarsicht/ANC-1/Syne/homology (KASH)/Sad-1/UNC-84 (SUN) protein pairs can act as connectors between cytoplasmic organelles and the nucleoskeleton. Caenorhabditis elegans ZYG-12 and SUN-1 are essential for centrosome-nucleus attachment. Although SUN-1 has a canonical SUN domain, ZYG-12 has a divergent KASH domain. Here, we establish that the ZYG-12 mini KASH domain is functional and, in combination with a portion of coiled-coil domain, is sufficient for nuclear envelope localization. ZYG-12 and SUN-1 are hypothesized to be outer and inner nuclear membrane proteins, respectively, and to interact, but neither their topologies nor their physical interaction has been directly investigated. We show that ZYG-12 is a type II outer nuclear membrane (ONM) protein and that SUN-1 is a type II inner nuclear membrane protein. The proteins interact in the luminal space of the nuclear envelope via the ZYG-12 mini KASH domain and a region of SUN-1 that does not include the SUN domain. SUN-1 is hypothesized to restrict ZYG-12 to the ONM, preventing diffusion through the endoplasmic reticulum. We establish that ZYG-12 is indeed immobile at the ONM by using fluorescence recovery after photobleaching and show that SUN-1 is sufficient to localize ZYG-12 in cells. This work supports current models of KASH/SUN pairs and highlights the diversity in sequence elements defining KASH domains.