The nucleotide and amino acid sequences of rat preprocholecystokinin and porcine preprogastrin have been aligned and their secondary structures predicted. Both precursors are predicted to be largely in turn and helical configurations. The sequence homology and position of an intron which splits the preprohormones suggest their evolution from a common ancestral protein. Preprohormone structure Cholecystokinin Gastrin. © 1985.