The complete cDNA structure of the Ap1y.w californm pro-protein and pro-hormone convertase PC2 (aPC2) was obtained from a cDNA library of the nervous system. The deduced amino acid sequence revealed that aPC2 exhibits an 85%, 61% and 62% sequence identity to the L~~naea stagnalis, Xenopus laevis and mouse PC2 homologues, respectively. The deduced primary sequence suggested a protein of 653 ammo acids which includes a 27-and 88-amino acid signal peptide and pro-segment.The signal peptide and the C-termmal segments are the least conserved regions. On Northern blots of nervous system we detected a transcript of 6.8 kb. The m situ hybridization histochermstry on the abdominal ganglion revealed intense labeling of the bag cells. Large peptidergic cells and clusters of sensory and motor neurons also contained high levels of aPC2 mRNA.