Taking tea with actin and microtubules

Microtubule plus ends may control sites of cell polarity and cytokinesis in both animal and yeast cells, but the mechanisms behind this have remained obscure. Now Fred Chang and colleagues at Columbia University, New York, NY, have detected a protein complex in Schizosaccharomyces pombe that links the actin- and microtubule-based cytoskeletal systems. Its existence also suggests that microtubule plus ends polarize cells by targeting cell-polarity factors to the cell surface.

The two proteins that coimmunoprecipitate are the microtubule-associated Tea1 protein and the actin-associated Bud6 protein. Tea1p is constantly deposited at cell tips by the plus ends of microtubules. The cell end that has grown before does not need Tea1p to continue growing, but delivery of Tea1p to the new end is apparently necessary for both the initiation of new growth and, according to Chang, the maintenance of Bud6p at this site. The two proteins are found in large multiprotein complexes that may drive the formation of actin-based structures necessary for growth. ▪