A Drosophila photoreceptor cell-specific protein, calphotin, binds calcium and contains a leucine zipper.

Abstract

The calphotin protein, encoded by the calphotin (cap) gene, is expressed in the soma and axons of all DrosophUa photoreceptor cells. It is expressed early in photoreceptor cell development, at the time when cell-type decisions are being made. Expression of calphotin is not altered by the glass mutation, which blocks photoreceptor cell development. The calphotin protein binds calcium and contains a long C-terminal leucine zipper. Potential implications of these properties are discussed.

Calphotin: a Drosophila photoreceptor cell calcium-binding protein.

“…7). The same gene for calphotin is described in the accompanying paper by Ballinger et al (10). The nucleotide sequences are nearly identical; both clones were derived from Canton S strains but from different cDNA libraries with possible polymorphisms.…”

“…It is identified by monoclonal antibody (mAb) 23E9 in the photoreceptor cell cytoplasm within a structure that extends along the length of the cell, parallel to but separated from the rhabdomere, and into the axon. As described in an accompanying paper, Ballinger et al (10) (12). Drosophila melanogaster wild-type (Canton S), white-eyed mutants, and eyes absent (eya) mutant (13) were raised at 250C on cornmeal medium.…”

Molecular Cloning of the Crustacean DD4 cDNA Encoding a Ca2+-Binding Protein

“…Calphotin is expressed specifically in photoreceptor cells and localized in cytoplasmic compartments where calcium precipitates of unknown crystalline structure are observed (11). Calphotin binds Ca 2ϩ , and therefore is implicated in formation of the Ca precipitates, although its precise role is unknown (11,12). Similarly, the role of DD4 in the calcification process remains to be elucidated.…”

“…A protein sequence database (DNA Databank of Japan 'Protein All' database (version 3.0t84) which included PIR and Swiss Prot) was sought using the FASTA program (10) to find proteins homologous to DD4. Calphotin, a Ca 2ϩ -binding protein expressed in photoreceptor cells of Drosophila melanogaster (11,12), was found to be the most similar, though the similarity score was not very high (optimized similarity score and z-score were 304 and 315.3, respectively). In the optimized alignment in which gaps were allowed, 26.7% identity was found at the amino acid level over the entire DD4 protein, but no regions of high similarity were found (data not shown).…”

RNA editing in Drosophila melanogaster: New targets and functional consequences

“…Nckx30C is critical for the rapid extrusion of calcium and is expressed in adult neurons and during ventral nerve cord development in the embryo (HaugCollet et al 1999). Cpn encodes a photoreceptor cellspecific calcium ion binding protein (Ballinger et al 1993;Martin et al 1993), and CG32699 is a gene that has an assigned GO functional attribute as having ''calcium ion binding with acyltransferase activity. ''…”