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G proteins find partners

The Journal of Cell Biology
The Rockefeller University Press
Publication Date
DOI: 10.1083/jcb1716rr3
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1716rr RESEARCH ROUNDUP • THE JOURNAL OF CELL BIOLOGY 915 Text by Nicole LeBrasseur [email protected] G proteins find partners n recent years, scientists have iden- tified many complexes containing most or all of the components needed to mount a particular signaling cascade. In contrast, Peter Hein, Moritz Bünemann (University of Würzburg, Germany), and colleagues find that a G protein signaling pathway works just as well, if not better, when receptor and G protein start out apart. Several groups have hypothesized that speed and specificity of the many different G protein–mediated pathways might be achieved by precoupling the G protein and its receptor, via direct or indirect binding. But the new FRET analyses show that the two are not together until the receptor is activated. Interactions I History’s influence on actin n imposed load on an actin network leads to exuberant growth when the pressure is released, say Sapun Parekh, Ovijit Chaudhuri, Julie Theriot, and Daniel Fletcher (University of California, Berkeley, CA). Thus, history matters when it comes to actin growth dynamics. Parekh et al. slowly increased the load pushing against a polymerizing actin network and measured network growth velocity along the way. Velocity remained constant for a while and then slowed as the load approached a stall-inducing maximum. The authors then returned the system to a lighter load and found that the network grew much faster—even faster than it did previously at this lighter load. A sudden burst of polymerization like that might help a migrating cell push quickly through a weak spot in the surrounding tissue. To explain how multiple velocities can exist for a given force, Fletcher suggests, “maybe the network is adapting to different loads.” Force- mediated activation of Arp2/3, for instance, would increase branching. “With higher load,” he explains, “you’d get a net addition in the number of filaments that are pushing the load. When the load is

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