Kin4mediated

Kin4-mediated refers to cellular processes controlled by the Saccharomyces cerevisiae protein kinase Kin4, with a primary role in the spindle position checkpoint that governs progression out of mitosis. Kin4 is a serine/threonine kinase that localizes to the mother cell cortex for much of the cell cycle and becomes involved in coordinating the mitotic exit network (MEN) with spindle alignment during division.

In the spindle position checkpoint, Kin4 acts to prevent premature mitotic exit when the mitotic spindle is misoriented. It contributes to maintaining Tem1, the key GTPase that activates the MEN, in an inactive state by affecting the activity of the Bfa1-Bud2 complex, a regulator of Tem1. Through phosphorylation events and cortical localization, Kin4 reinforces the checkpoint so that the MEN is not triggered until the spindle is correctly aligned along the mother–daughter axis.

When the spindle is properly positioned and one spindle pole enters the daughter cell, Kin4 activity is diminished or relocated, allowing the daughter-cell–restricted factor Lte1 to promote Tem1 activation. This shift enables the MEN to drive mitotic exit and progression to cytokinesis. Kin4’s function is tightly linked to spatial cues and cell polarity, ensuring that chromosome segregation is coordinated with accurate cell division.

Research on Kin4-mediated processes provides insights into how spatial regulation interfaces with cell cycle control in yeast. While Kin4 is well characterized in S. cerevisiae, its direct homologs and functional parallels in other organisms are more limited, reflecting lineage-specific adaptations of the spindle position checkpoint.