Summary In budding yeast, over 60 proteins functioning in at least 5 modules are recruited to endocytic sites with predictable order and timing. However, how sites of clathrin-mediated endocytosis are initiated and stabilized is not well understood. Here, the casein kinase 1 (CK1) Hrr25 is shown to be an endocytic protein and to be among the earliest proteins to appear at endocytic sites. Hrr25 absence or overexpression decreases or increases the rate of endocytic site initiation, respectively. Ede1, an early endocytic Eps15-like protein important for endocytic initiation, is an Hrr25 target and is required for Hrr25 recruitment to endocytic sites. Hrr25 phosphorylation of Ede1 is required for Hrr25-Ede1 interaction and promotes efficient initiation of endocytic sites. These observations indicate that Hrr25 kinase and Ede1 cooperate to initiate and stabilize endocytic sites. Analysis of the mammalian homologs CK1δ/ε suggests a conserved role for these protein kinases in endocytic site initiation and stabilization.

Ipl1/Aurora-mediated phosphorylation of the CPC component Sli15/INCENP promotes microtubule dynamics by restricting CPC–spindle association.

Vac8p, an armadillo (ARM) repeat protein, is required for multiple vacuolar processes. It functions in vacuole inheritance, cytoplasm-to-vacuole protein targeting pathway, formation of the nucleus-vacuole junction and vacuolevacuole fusion. These functions each utilize a distinct Vac8p-binding partner. Here, we report an additional Vac8p function: caffeine resistance. We show that Vac8p function in caffeine resistance is mediated via a newly identified Vac8p-binding partner, Tco89p. The interaction between Vac8p and each binding partner requires an overlapping subset of Vac8p ARM repeats. Moreover, these partners can compete with each other for access to Vac8p. Furthermore, Vac8p is enriched in three separate subdomains on the vacuole, each with a unique binding partner dedicated to a different vacuolar function. These findings suggest that a major role of Vac8p is to spatially separate multiple functions thereby enabling vacuole inheritance to occur concurrently with other vacuolar processes.

Kinetochores are large multiprotein complexes that mediate chromosome segregation in all eukaryotes by dynamically connecting specialized chromosome regions, termed centromeres, to the plus-ends of spindle microtubules. Even the relatively simple kinetochores of the budding yeast Saccharomyces cerevisiae consist of more than 80 proteins, making analysis of their respective roles a daunting task. Here, we have developed a system that allows us to artificially recruit proteins to DNA sequences and determine whether they can provide any aspect of kinetochore function in vivo. We show that artificial recruitment of the microtubule-binding Dam1 complex to a plasmid lacking any centromere DNA is sufficient to confer mitotic stabilization. The Dam1-based artificial kinetochores are able to attach, bi-orient and segregate mini-chromosomes on the mitotic spindle, and they bypass the requirement for essential DNA-binding components of natural kinetochores. Thus, we have built a simplified chromosome segregation system by directly recruiting a microtubule force-transducing component to DNA.