title: Calphotin: a Drosophila photoreceptor cell calcium-binding protein.
abstract: Monoclonal antibody 23E9 identifies a calcium-binding protein, calphotin, in photoreceptor cells of the Drosophila melanogaster compound eyes and ocelli. The antigen is restricted to a defined cytoplasmic region; it is not present in the rhabdomeres, nuclei, mitochondria, or rough endoplasmic reticulum. A corresponding cDNA recognizes a 3-kb mRNA with retinal specificity similar to the antigen and maps to band 86E/F-87A/B on chromosome 3. An open reading frame of 2595 bp encodes an estimated 85-kDa protein of unusual amino acid composition, with > 50% proline, alanine, and valine and very few basic residues. The C-terminal segment contains a leucine zipper motif uninterrupted by prolines. We found no significant similarities with the GenBank or National Biomedical Resource Foundation data bases. The location of the protein within a distinct cytoplasmic region suggests that it might function as a calcium-sequestering "sponge" to regulate the amount of free cytoplasmic calcium.
authors.affiliation: Department of Pathology, University of Southern California School of Medicine, Los Angeles 90033.
authors.forename: J H
authors.initials: JH
authors.lastname: Martin
authors.forename: S
authors.initials: S
authors.lastname: Benzer
authors.forename: M
authors.initials: M
authors.lastname: Rudnicka
authors.forename: C A
authors.initials: CA
authors.lastname: Miller
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D000911:Antibodies, Monoclonal; D001483:Base Sequence; D015152:Blotting, Northern; D002118:Calcium / Q000378:metabolism; D002135:Calcium-Binding Proteins / Q000032:analysis / Q000235:genetics* / Q000378:metabolism*; D016208:Databases, Factual; D029721:Drosophila Proteins; D004331:Drosophila melanogaster / Q000502:physiology*; D015723:Gene Library; D015151:Immunoblotting; D017403:In Situ Hybridization; D007301:Insect Hormones / Q000235:genetics* / Q000378:metabolism*; D019476:Insect Proteins; D016350:Leucine Zippers / Q000235:genetics; D008854:Microscopy, Electron; D008969:Molecular Sequence Data; D010786:Photoreceptor Cells / Q000378:metabolism* / Q000648:ultrastructure; D011061:Poly A / Q000032:analysis / Q000235:genetics / Q000378:metabolism; D012333:RNA, Messenger / Q000032:analysis / Q000235:genetics / Q000378:metabolism
chemical_list: D000911:Antibodies, Monoclonal; D002135:Calcium-Binding Proteins; C079658:Cpn protein, Drosophila; D029721:Drosophila Proteins; D007301:Insect Hormones; D019476:Insect Proteins; D012333:RNA, Messenger; D011061:Poly A; D002118:Calcium