Structure of soybean Kunitz trypsin inhibitor mRNA determined from cDNA by using oligodeoxynucleotide primers

Oligodeoxynucleotides complementary to the deduced mRNA sequence of soybean Kunitz trypsin inhibitor (KTI) were used to prime the synthesis of cDNA from soybean cotyledon total poly(A) RNA. The primed cDNA was used to select clones from a Glycine max cotyledon cDNA library. Two out of twelve hybridizing clones were shown to contain KTI cDNA. The nucleotide sequence of one clone, pSTI 9-2, was determined and it was found to encompass the complete protein coding region of KTI excet for three C-terminal residues. Trypsin inhibitor is synthesized with a 25 amino acid hydrophobic N-terminal sequence presumed to be a signal peptide. The mature polypeptide encoded by pSTI 9-2 agrees with the published amino acid composition of KTI, but contains two discrepancies at the peptide sequence level.