CLONING AND CHARACTERIZATION OF A CALCIUM-CHANNEL SUBUNIT FROM DROSOPHILA-MELANOGASTER WITH SIMILARITY TO THE RAT-BRAIN ALPHA(1)-TYPE-D ISOFORM

We report the complete sequence of al calcium channel alpha(1) subunit cDNA cloned from a Drosophila head cDNA library. This cDNA encodes a deduced protein containing 2516 amino acids with a predicted molecular weight of 276,493. The deduced protein shares many features with vert ebrate homologs, including four repeat structures, each containing six transmembrane domains, a conserved ion selectivity filter region betw een transmembrane domains 5 and 6, and an EF hand in the carboxy tail. The Drosophila subunit has unusually long initial amino and terminal carboxy tails. The region corresponding to the last transmembrane doma in (IVS6) and the adjacent cytoplasmic domain has been postulated to f orm a phenylalkylamine-binding site in vertebrate calcium channels. Th is region is conserved in the Drosophila sequence, while domains thoug ht to be involved in dihydropyridine binding show numerous changes. Th e Drosophila subunit exhibits 78.3% sequence similarity to the rat bra in type D calcium channel alpha(1) subunit, and so has been designated as a Drosophila melanogaster calcium channel alpha(1) type D subunit (Dmca 1D). In situ hybridization shows that Dmca 1D is highly expresse d in the embryonic nervous system. Northern analysis shows that D,ca 1 D D cDNA hybridizes to three size classes of mRNA (9.5, 10.2, and 12.5 kb) in heads, but only two classes (9.5 and 12.5 kb) in bodies and le gs. PCR analysis suggests that the Dmca 1D message undergoes alternati ve splicing with more heterogeneity appearing in head and embryonic ex tracts than in bodies and legs.