title: Molecular cloning and characterization of rab27a and rab27b, novel human rab proteins shared by melanocytes and platelets.
abstract: Rabs are prenylated, membrane-bound proteins involved in vesicular fusion and trafficking. We isolated the complete cDNAs of two rab isoforms, rab27a and rab27b, from human melanoma cells and melanocytes, Rab27a is the human homolog of a rat megakaryocyte rab called ram p25. Rab27b corresponds to a small GTP-binding protein, c25KG, which was previously purified from platelets but whose cDNA had not been cloned. Sequence comparisons with known rabs indicate that rab27a and rab27b comprise a melanocyte/platelet subfamily within the rab family. In addition, rab27a was expressed in a large variety of cell and tissue types, excluding brain, and rab27b manifested itself primarily in testis. Bacterially expressed and purified rab27a and rab27b exhibited GTP-binding activity and can now be used for antibody production and studies of the substrate specificities of geranylgeranyl transferase. In addition, the expression of rab27a and rab27b in both melanocytes and platelets makes them candidates for involvement in mouse and human disorders characterized by the combination of pigment dilution and a platelet storage pool defect.
authors.affiliation: Section on Human Biochemical Genetics, National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland 20892, USA.
authors.forename: D
authors.initials: D
authors.lastname: Chen
authors.forename: J
authors.initials: J
authors.lastname: Guo
authors.forename: T
authors.initials: T
authors.lastname: Miki
authors.forename: M
authors.initials: M
authors.lastname: Tachibana
authors.forename: W A
authors.initials: WA
authors.lastname: Gahl
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D001792:Blood Platelets / Q000166:cytology / Q000378:metabolism*; D003001:Cloning, Molecular; D018076:DNA, Complementary; D019204:GTP-Binding Proteins / Q000145:classification / Q000235:genetics* / Q000378:metabolism; D006801:Humans; D008544:Melanocytes / Q000166:cytology / Q000378:metabolism*; D008545:Melanoma; D008969:Molecular Sequence Data; D017386:Sequence Homology, Amino Acid; D009626:Terminology as Topic; D014407:Tumor Cells, Cultured; D020691:rab GTP-Binding Proteins; D000075745:rab27 GTP-Binding Proteins
chemical_list: D018076:DNA, Complementary; D000075745:rab27 GTP-Binding Proteins; D019204:GTP-Binding Proteins; C512958:Rab27b protein, mouse; C512956:Rab27b protein, rat; C066694:RAB27A protein, human; C512960:Rab27B protein, human; C512962:Rab27a protein, mouse; C512961:Rab27a protein, rat; D020691:rab GTP-Binding Proteins