Molecular characterization and expression of the Drosophila Ca2+/calmodulin-dependent protein kinase II gene. Identification of four forms of the enzyme generated from a single gene by alternative splicing.

Four cDNA sequences encoding Ca2+/calmodulin-dependent protein kinase II (CaM kinase II) were isolated from a Drosophila adult head cDNA library using rat CaM kinase II alpha and beta cDNA sequences under low stringency hybridization conditions. These cDNA clones encoded polypeptides of 490, 509, 516, and 530 amino acids, which are identical to one another except for amino acid insertions or deletions near the carboxyl-terminal of the putative "link" segment. These polypeptides showed considerable similarity to rat brain CaM kinase II with more than 70% of the amino acids being identical. The Drosophila adult head contains three major species of CaM kinase II with molecular masses of 55, 58, and 60 kDa. These cross-react with anti-rat CaM kinase II antibody. An expression study of the four cDNA sequences in mammalian cells revealed that the polypeptides of 490, 509, and 530 amino acids that had been predicted from the cDNA sequences correspond to the 55-, 58-, and 60-kDa polypeptides found in the head, respectively, and all exhibited enzymatic properties similar to those of rat brain CaM kinase II, including self-regulation. The Drosophila CaM kinase II gene was located in segment 102E-F on the fourth chromosome and consisted of at least 16 exons spanning approximately 20 kilobase pairs. Four forms of the enzyme are generated from a single gene by alternative splicing. Transcripts of CaM kinase II are expressed in great quantities in the central nervous system in the late embryonic stage of development and are more abundant in the head than in the body of the adult fly.