Cell Biology

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Science  09 Mar 2001:
Vol. 291, Issue 5510, pp. 1861
DOI: 10.1126/science.291.5510.1861b

That the Rab family of GTPases functions in the targeting of intracellular vesicles during membrane traffic is well established. Several groups now have extended the remit of the Rab family into the motility arena. Each type of intracellular vesicle is identified by a set of Rab proteins; these specify where it has come from and where it should go. The protein Rab 27a specifically marks two types of secretory lysosomes, the melanosomes (pigment granules) in melanocytes and the cytotoxic granules in cytotoxic T lymphocytes (CTLs).

In CTLs, Stinchcombe et al. and Haddad et al. show that Rab27a is required for the correct localization and secretion of cytotoxic granules. They also show that these processes are disrupted in ashen (possessing a mutated Rab27a) and gunmetal (carrying a defective Rab-modifying enzyme) mice, which serve as animal models for the Grischelli and Hermansky-Pudlak syndromes, respectively. From experiments in melanocytes, Hume et al., Bahadoran et al., and Wu et al. show that Rab27a mediates the correct localization of melanosomes to the periphery of the cell via interaction with the motor protein myosin Va. — SMH

J. Cell Biol.152, 825; 835; 795; 843 (2001); J. Cell Sci., in press.

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