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RM proteins link adhesion molecules to the cytoskeleton, but this linkage must be restricted to the necessary place and time. Structural analyses by Toshio Hakoshima (Nara Institute of Science and Technology , Nara, Japan) suggest that phospholipids take care of this regulation. Inactive ERMs, such as radixin, are folded to mask both their actin-and adhesion protein–binding (FERM) domains. This fold is lost in vitro if either the actin-binding domain is phosphorylated or the FERM domain binds to PIP 2. Both modifications occur in vivo, so Hakoshima examined which was critical for radixin activation. The analysis revealed that the phospholipid binding activates ERMs. In the radixin crystal structure, the PIP 2-binding site was accessible in the folded form, whereas the phosphorylation site was buried within the interface. Phospholipid binding to FERM opened the structure, thus exposing both actin-and adhesion molecule–binding sites. ome kinesins destroy microtubules by chewing them up. But others have stabilizing effects that have not been explained. presented evidence that, in yeast, these motors can be stabilizing because they deliver plus-end binding proteins to microtubule tips. In budding yeast, astral microtubules are more stable during mitosis than during inter-phase, which allows them to grow toward the bud site for correct spindle positioning. Pellman finds that these changes in microtubule stability correlate with fluctuations in the levels of the Kip2 kinesin. Pellman was able to track this motor and its cargo on individual microtubules. Kip2's cargo included Bik1, a plus-end binding protein known to stabilize microtubules. During mitosis, Kip2 levels were highest and so Bik1 was carried out to the plus ends. Kip2 was also needed to bring dynein, a minus-end– directed motor needed to pull the spindle into the bud at anaphase, to microtubule plus ends. From there, dynein was transferred to the cortex. A receptor on the cortex, possibly Num1, seems to activate dynein. " When [dynein] hits the cortex, we see showers of [dynein] speckles tracking toward the minus ends, " says Pellman. Kip2 levels are low until mitosis, so the plus ends of interphase microtubules have less dynein and Bik1. Their absence seems to favor other plus-end binding proteins, such as Kar9, which works with a myosin in G 1 to guide spindle microtubules to the bud site. ᭿ S Kip2 (red) takes Bik1 (green) to the plus ends of microtubules. PIP 2-mediated activation restricts ERM opening to the membrane. Adhesion molecules can then lock the …