Model for PA domain–mediated patch assembly and dynein anchoring. (A, left) dimeric Num1 molecules are preferentially recruited to plasma membrane domains recognized by its N-terminal PA domain. Upon binding to the membrane, Num1 dimers further assemble into stationary patches through self-association. The dimer–dimer association of Num1 requires its PA domain and can be disrupted by the E191A + K192A mutation or by deleting the CC1 motif. On the other hand, the PH domain located at the C terminus of Num1 contributes to its membrane association by binding to membrane PI(4,5)P₂. (right) The dynein complex associated with the plus end of astral microtubules (MT) interacts with the membrane-bound Num1, thereby becoming anchored at the cell cortex. Interaction of Num1 with dynein is mediated by the PA domain and can be abolished by the L167E + L170E mutation located within the PA domain. (B) Dynein anchored to the Num1 patch pulls the nucleus and its associated spindle from the mother to the bud through the narrow bud neck. Although dynein is able to bind Num1 patches of variable sizes, anchoring to large patches enhances its activity and facilitates pulling of the spindle through the bud neck.