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J. Cell Biol.,
Volume 142, Number 4, August 24, 1998 1001-1012
* Department of Biology, University of Pennsylvania; and Cdc42, activated with GTP Electron microscopy revealed that Cdc42-induced filaments elongated rapidly, achieving a mean length
greater than 1 µm in 15 s. The mean length of filaments
formed from spectrin-actin seeds was <0.4 µm. Had
spectrin-actin seeds elongated at comparable rates before they were capped, they would have induced longer filaments. There was little change in mean length of
Cdc42-induced filaments between 15 s and 5 min, suggesting that the increase in F-actin over this time was
due to an increase in filament number. These data suggest that Cdc42 induction of actin polymerization requires both creation of free barbed ends and facilitated
elongation at these ends.
Department of Physiology, University of Pennsylvania Medical
School, Philadelphia, Pennsylvania 19104-6018
S, induces actin
polymerization in supernatants of lysed neutrophils.
This polymerization, like that induced by agonists, requires elongation at filament barbed ends. To determine if creation of free barbed ends was sufficient to induce actin polymerization, free barbed ends in the form
of spectrin-actin seeds or sheared F-actin filaments
were added to cell supernatants. Neither induced polymerization. Furthermore, the presence of spectrin-actin
seeds did not increase the rate of Cdc42-induced polymerization, suggesting that the presence of Cdc42 did
not facilitate polymerization from spectrin-actin seeds
such as might have been the case if Cdc42 inhibited
capping or released G-actin from a sequestered pool.
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