Genetic characterization of a novel soybean Kunitz trypsin inhibitor

Genetic and nucleotide sequence studies were performed on a new variant of soybean Kunitz trypsin inhibitor (SKTI) detected in wild soybean (Glycine soja) and showing a slightly slower electrophoretic mobility than the Tia type. The segregation analysis of SKTI bands in F-2 seeds from crosses of the new variant type with Tia or Tib type showed that the variant type is controlled by an allele codominant to Tia and Tib at an SKTI locus. Nucleotide sequence analysis showed that this variant has 217 amino acids composed of 181 amino acid residues of mature SKTI and extra 25 and 11 amino acids at N- and C-terminal regions, respectively. This sequence was identical to that of Tia (= KTi3), except that a G --> A transitional mutation occurred at position 500 of Tia, which results in the translational change from Arg to Lys. The result of isoelectric. forcusing-PAGE coincided with this change. In addition, three nucleotides GCT were inserted at the N-terminus, which leads to an Ala addition in the precursor of this SKTI protein. From these results, we propose the genetic symbol Tie for the new variant of SKTI.