Nud1

Nud1 is a spindle pole body–associated scaffold protein in the budding yeast Saccharomyces cerevisiae. Encoded by the NUD1 gene, Nud1 functions as a central organizer of the mitotic exit network (MEN), a signaling module that coordinates the final stages of mitosis and cytokinesis. By acting as a docking platform at the spindle pole body, Nud1 helps coordinate the activity and localization of key MEN components, enabling a timely exit from mitosis.

Localization and function

Nud1 localizes to the spindle pole body throughout the cell cycle and serves as a scaffold for MEN signaling. It recruits and anchors essential kinases and regulators, including Cdc15 and the Dbf2–Mob1 complex, to the spindle pole body. Through these interactions, Nud1 promotes the activation of the Cdc14 phosphatase, facilitating its release from the nucleolus and driving mitotic exit. This scaffolding role helps ensure that mitotic exit occurs only after proper spindle positioning and chromosome segregation.

Genetic and regulatory aspects

Nud1 operates upstream within the MEN cascade and interacts genetically with other MEN components such as Tem1 and Bfa1–Bub2. Its activity is modulated by phosphorylation, a regulatory mechanism that influences its capacity to recruit and organize MEN kinases at the spindle pole body. Loss or alteration of Nud1 function typically results in delays or arrest during late mitosis, reflecting its essential role in completing cell division.

Structure and evolution

Nud1 is a relatively large, coiled-coil–rich protein that provides multiple binding surfaces at the spindle pole body. While best characterized in budding yeast, the concept of SPB or centrosome–associated scaffolds organizing mitotic exit signaling is a common theme across eukaryotes, with different organisms employing their own scaffold proteins to coordinate analogous processes.

See also: Mitotic exit network, Cdc14, Cdc15, Dbf2–Mob1, Tem1.