AN INVERTEBRATE CALCIUM-BINDING PROTEIN OF THE CALBINDIN SUBFAMILY - PROTEIN-STRUCTURE, GENOMIC ORGANIZATION, AND EXPRESSION PATTERN OF THECALBINDIN-32 GENE OF DROSOPHILA

Antisera against vertebrate calcium-binding proteins cross-react with Drosophila nervous and muscle tissue. We have used an antiserum agains t carp parvalbumin to isolate from a Drosophila head cDNA library immu nopositive expression clones. Tissue in situ hybridization identified a clone that labeled specific neurons and muscles similar to the parva l-bumin-like immunohistochemical staining pattern. Five independent cD NAs derive from an mRNA whose open reading frame codes for a 310 amino acid polypeptide. Sequence analysis identifies six EF-hand calcium-bi nding domains and reveals 42% and 37% homology to chicken calretinin a nd calbindin D-28k, respectively. Since the positions of 9 out of 10 i ntrons within the ORF are conserved from the Drosophila gene to both v ertebrate genes, we conclude that we have identified the first inverte brate member of the calbindin subfamily of calcium-binding protein gen es of the EF-hand homolog family. The calbindin-32 gene (cbn) maps to 53E on the second chromosome. It is expressed through most of ontogene sis with a selective distribution in the nervous system and in a few s mall adult thoracic muscles. The cloning of a Drosophila homolog to ve rtebrate neuronal Ca2+-binding proteins opens new routes to study the so far largely elusive function of these brain molecules.