title: Defective expression of the mu3 subunit of the AP-3 adaptor complex in the Drosophila pigmentation mutant carmine.
abstract: The adaptor protein (AP) complexes AP-1, AP-2, and AP-3 mediate coated vesicle formation and sorting of integral membrane proteins in the endocytic and late exocytic pathways in mammalian cells. A search of the Drosophila melanogaster expressed sequence tag (EST) database identified orthologs of family members mammalian medium (mu) chain families mu1, mu2, and mu3, of the corresponding AP complexes, and delta-COP, the analogous component of the coatomer (COPI) complex. The Drosophila orthologs exhibit a high degree of sequence identity to mammalian medium chain and delta-COP proteins. Northern analysis demonstrated that medium chain and delta-COP mRNAs are expressed uniformly throughout fly development. Medium chain and delta-COP genes were cytologically mapped and the mu3 gene was found to localize to a region containing the pigmentation locus carmine (cm). Analysis of genomic DNA of the cm1 mutant allele indicated the presence of a large insertion in the coding region of the mu3 gene and Northern analysis revealed no detectable mu3 mRNA. Light microscopy of the cm1 mutant showed a reduction in primary, secondary, and tertiary pigment granules in the adult eye. These findings provide evidence of a role for mu3 in the sorting processes required for pigment granule biogenesis in Drosophila.
authors.affiliation: Cell Biology and Metabolism Branch, National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD 20892, USA.
authors.forename: C
authors.initials: C
authors.lastname: Mullins
authors.forename: L M
authors.initials: LM
authors.lastname: Hartnell
authors.forename: D A
authors.initials: DA
authors.lastname: Wassarman
authors.forename: J S
authors.initials: JS
authors.lastname: Bonifacino
mesh_terms: D033961:Adaptor Protein Complex 1; D033962:Adaptor Protein Complex 2; D033963:Adaptor Protein Complex 3; D033965:Adaptor Protein Complex alpha Subunits; D033983:Adaptor Protein Complex mu Subunits; D033942:Adaptor Proteins, Vesicular Transport; D016115:Albinism, Oculocutaneous / Q000235:genetics; D000595:Amino Acid Sequence; D000818:Animals; D001692:Biological Transport; D002874:Chromosome Mapping; D020755:Coat Protein Complex I / Q000235:genetics*; D003594:Cytoplasmic Granules; D004331:Drosophila melanogaster / Q000196:embryology / Q000235:genetics*; D011992:Endosomes; D019143:Evolution, Molecular; D020224:Expressed Sequence Tags; D008247:Lysosomes; D008565:Membrane Proteins / Q000235:genetics*; D008969:Molecular Sequence Data; D034041:Monomeric Clathrin Assembly Proteins; D009154:Mutation; D017956:Photoreceptor Cells, Invertebrate / Q000648:ultrastructure*; D010858:Pigmentation / Q000235:genetics*; D051381:Rats; D017386:Sequence Homology, Amino Acid
chemical_list: D033961:Adaptor Protein Complex 1; D033962:Adaptor Protein Complex 2; D033963:Adaptor Protein Complex 3; D033965:Adaptor Protein Complex alpha Subunits; D033983:Adaptor Protein Complex mu Subunits; D033942:Adaptor Proteins, Vesicular Transport; C510072:Ap3m2 protein, rat; D020755:Coat Protein Complex I; D008565:Membrane Proteins; D034041:Monomeric Clathrin Assembly Proteins; C499066:adaptor protein complex 1, mu 1 subunit; C499065:adaptor protein complex 1, mu 2 subunit; C438885:adaptor protein complex 2, mu 1 subunit; C438886:adaptor protein complex 2, mu 2 subunit; C439023:clathrin assembly protein AP180