Kinase interplay centered on two regulatory elements compartmentalizes the checkpoint protein Lte1 in S. cerevisiae

In budding yeast, Lte1, a component of the spindle position checkpoint, must be confined to the bud for correctly coupling chromosomal segregation across the bud neck with mitotic exit. Bud compartmentalization involves a phospho-dependent program with Ras-GTP acting as the ultimate cortical anchor. Here, we have dissected this program by identifying an Lte1 domain participating in Ras binding and two phospho-regulatory motifs, the N- and C-Lte1 regulatory elements (LREs). The C-LRE mediates control of Lte1 cortical recruitment by the p21-activated kinase, Cla4. The N-terminal LRE modulates Lte1 binding to Ras more directly and is phosphorylated by the yeast MARK/PAR-1 protein kinases, Kin1/2. Along with previously described cyclin-dependent kinase phosphorylation sites, the N- and C-LREs are required for Lte1 localization and timely mitotic exit. These studies uncover the coordinated interplay between multiple protein kinases, allowing Lte1 to integrate cell polarity and cell cycle cues for strict compartmentalization at the bud cell cortex.