Secretion is polarized into the yeast bud so that the bud grows in preference to the mother cell. Pruyne et al. (page ) report that this actin-based process is directed by actin fibers that extend into the bud, and not by the actin patches that are clustered near the bud tip.
Most perturbations to the actin system depolarize both patches and cables, but Pruyne et al. find that the combination of a temperature-sensitive tropomyosin 1 mutation and a tropomyosin 2 deletion can be used to selectively rid the cell of cables. Tropomyosin is found on, and stabilizes, actin cables but is not present in actin patches.
Actin cables disappear just one minute after shifting the double mutant to a restrictive temperature; another minute later two other molecules are no longer concentrated at the bud tip. These proteins—Sec4, a secretory vesicle GTPase, and Myo2p, an unconventional myosin V implicated in...
