Role of bud6p and tea1p in the interaction between actin and microtubules for the establishment of cell polarity in fission yeast

Background: In many cell types, microtubules are thought to direct the spat ial distribution of F-actin in cell polarity. Schizosaccharomyces pombe cel ls exhibit a regulated program of polarized cell growth: after cell divisio n, they grow first in a monopolar manner at the old end, and in G2 phase, i nitiate growth at the previous cell division site (the new end), The role o f microtubule ends in cell polarity is highlighted by the finding that the cell polarity factor, tea1p, is present on microtubule plus ends and cell t ips [1]. Results: Here, we characterize S, pombe bud6p/fat1p, a homolog of S. cerevi siae Bud6/Aip3, bud6 Delta mutant cells have a specific defect in the effic ient initiation of growth at the new end and like tea Ih cells, form T-shap ed cells in a cdc11 background. Bud6-GFP localizes to both cell tips and th e cytokinesis ring, Maintenance of cell tip localization is dependent upon actin but not microtubules. Bud6-GFP localization is tea1p dependent, and t ea1p localization is not bud6p dependent. tea1 Delta and bud6 Delta cells g enerally grow in a monopolar manner but exhibit different growth patterns. tea1 Delta bud6 Delta mutants resemble tea1 Delta mutants. Tea1p and bud6p coimmunoprecipitate and comigrate in large complexes. Conclusions: Our studies show that tea1p (a microtubule end-associated fact or) and bud6p (an actin-associated factor) function in a common pathway, wi th bud6p downstream of tea1p. To our knowledge, bud6p is the first protein shown to interact physically with tea1p. These studies delineate a pathway for how microtubule plus ends function to polarize the actin cytoskeleton t hrough actin-associated polarity factors.