Microtubules concentrate

icrotubule plus ends may control sites of cell polarity and cytokinesis in both animal and yeast cells, but the mechanisms behind this have remained obscure. 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 coimmunopre-cipitate are the microtubule-associated Tea1 protein and the actin-associated Bud6 protein. Tea1p is constantly deposited at cell tips by the plus ends of micro-M tubules. 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. ᭿ switch from intramolecular to intermolecular disulfide bonds helps Hydra and related jellyfish to construct a capsule of enormous strength, according to a team of zoologists and biochemists. The capsule, actually a specialized organelle called a nematocyst, is used by Hydra for defense, locomotion, and prey capture. Nematocysts contain a high concentration of A poly-␥-glutamate, resulting in an internal pressure of up to 150 atmospheres that drives the explosive discharge of an internal spiny tubule when the organism is irritated or detects prey. This discharge has a maximum velocity of 2 m per second and an acceleration of 40,000 g , and is thus one of the fastest cellular processes in nature. Nematocysts must have a strong wall to contain such pressure. Jürgen Engel (University of Basel, Basel, Switzerland) and colleagues suspected that disulfides might be important, as reducing conditions cause nematocysts to burst. They examined disulfide formation in minicollagen-1, a nematocyst wall component, and found that minicollagen-1 synthesized either recently in vivo, or at any time in a recombinant system, has only intramolec-The minicollagen antibody (red) detects nematocysts (green) only in their immature form, before intermolecular disulfides form. ular disulfides. A switch from intramolecular to intermolecular disulfides, detected biochemically and as a reduction in antibody reactivity, was associated with hardening of the nematocyst wall. This process may be similar to the acquisition of intermolecular disulfides by mammalian collagen IV during basement-membrane formation. ᭿ and colleagues. The two Drosophila proteins, Mini-spindles (Msps) and D-TACC, have previously been shown to localize …