Nud1p links astral microtubule organization and the control of exit from mitosis

The budding yeast spindle pole body (SPB) not only organizes the astral and nuclear microtubules but is also associated with a number of cell-cycle re gulators that control mitotic exit. Here, me describe that the core SPB com ponent Nud1p is a key protein that functions in both processes. The astral microtubule organizing function of Nud1p is mediated by its interaction wit h the gamma -tubulin complex binding protein Spc72p. This function of Nud1p is distinct from its role in cell-cycle control: Nud1p binds the spindle c heckpoint control proteins Bfa1p and Bub2p to the SPB, and is part of the m itotic exit network (MEN) in which it functions upstream of CDC15 but downs tream of LTE1. In conditional lethal nud1-2 cells, the MEN component Tem1p, a GTPase, is mislocalized, whereas the kinase Cdc15p is still associated w ith the SPB. Thus, in nud1-2 cells the failure of Tem1p to interact with Cd c15p at the SPB probably prevents mitotic exit.