CALPA, A DROSOPHILA CALPAIN HOMOLOG SPECIFICALLY EXPRESSED IN A SMALLSET OF NERVE, MIDGUT, AND BLOOD-CELLS

Calpains are calcium-dependent proteases believed to participate in ca lcium-regulated signal pathways in cells. Ubiquitous calpains as well as tissue-specific calpains have been found in vertebrates. We isolate d cDNA clones for a highly tissue-specific calpain gene from Drosophil a melanogaster, CalpA, at 56C-D on the second chromosome. The expressi on of the CalpA gene product was monitored by using a specific antiser um directed against the product expressed by one cDNA clone. The encod ed protein is found in a few neurons in the central nervous system, in scattered endocrine cells in the midgut, and in blood cells. In the b lood cell line mbn-2, calpain is associated with a granular component in the cytoplasm. The expression of this protein is more restricted th an that of the corresponding transcripts, which are widely distributed in the central nervous system, digestive tract, and other tissues. Th e sequence of CalpA is closely related to that of vertebrate calpains, but an additional segment is inserted in the calmodulin-like carboxy- terminal domain, This insert contains a hydrophobic region that may be involved in membrane attachment of the enzyme. Differential splicing also gives rise to a minor transcript that lacks the calmodulin-like d omain.