It was widely thought that 3 variants of Kunitz type trypsin inhibitor(SBTi A 2) existed in soybean seed storage protein.Three of codominant alleles Ti a,Ti b and Ti c were identified to decode these SBTi A 2 inhibitors and the amino acid sequences of them were determined,of which one or more different amino acid were found.Ti d was a new variant allele of SBTi A 2 discovered after analyzing more than 15 000 samples of soybean seed in China.In order to study the structure features of Ti d protein,the amino acid sequence of this protein was deduced from its coding region which was amplified by PCR from soybean genomic DNA and sequenced.By comparison with Ti a protein,two different amino acid residue were found between Ti a and Ti d proteins.One was an extra Ala inserted in the signal peptide of Ti d,with 8 residues from N terminal,and the other existed in the mature protein,with Glu 69 in Ti a protein turned into Lys 69 in Ti d protein.The amino acid sequence of Ti d mature protein was also different from those of Ti a and Ti b.
About 1 kb fragment of rbcS (ribulose 1,5 bisphosphate carboxylase small subunit) gene in wild soybean (Glycine soja, Ji 50017) was amplified from total DNA by PCR assay. Sequence analysis of the fragment indicated that 1089 bp sequenced included the whole coding region for Rubisco small subunit. The rbcS gene in wild soybean encoded a precursor composed of a transit peptide of 55 amino acids and a mature protein of 123 amino acids. There were two introns found in the rbcS gene as other dicotyledonous species previously sequenced.Comparison of DNA sequences showed high degree homology of rbcS genes between wild soybean and cultivated soybean (Glycine max var. wayne). Some changes of amino acids emerged from the diverse nucleotides did not affect the function of the small subunit. These results may contribute some basic data in molecular biology to study the origin and evolution of soybean.
