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 (CAPL) containing two mutually exclusive exon cassettes. CAPL transcripts are present in several classes of identified neurons containing transmitter-sensitive 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.