Two catalytic subunits of cAMP-dependent protein kinase generated by alternative RNA splicing are expressed in Aplysia neurons

The amino acid sequences of two catalytic (C) subunits of Aplysia CAMP-dependent protein kinase (cAPK) have been deduced from the nucleotide sequences of cDNAs generated from neuronal poly(A)⁺ RNA. Both subunits contain 352 residues and are identical except for amino acids 142-183, which differ at 10 out of 42 positions. They derive from alternatively spliced transcripts of a single gene (C_APL) containing two mutually exclusive exon cassettes. C_APL transcripts are present in several classes of identified neurons containing transmittersensitive adenylate cyclase, including sensory cells, bag cells, and the left pleural giant cell. Combinatorial expression of the various regulatory (R) and C subunits might produce kinase isoforms with distinct roles in neuronal modulation. Alternatively, holoenzymes with overlapping properties together might contribute to the definition of individual cell types and physiological states.