Characterization of a low-molecular-weight glutenin subunit gene from bread wheat and the corresponding protein that represents a major subunit of the glutenin polymer

Both high- and low-molecular-weight glutenin subunits (LMW-GS) play the maj or role in determining the viscoelastic properties of wheat (Triticum aesti vum L.) flour. To date there has been no clear correspondence between the a mino acid sequences of LMW-GS derived from DNA sequencing and those of actu al LMW-GS present in the endosperm. We have characterized a particular LMW- GS from hexaploid bread wheat, a major component of the glutenin polymer, w hich we call the 42K LMW-GS, and have isolated and sequenced the putative c orresponding gene. Extensive amino acid sequences obtained directly for thi s 42K LMW-GS indicate correspondence between this protein and the putative corresponding gene. This subunit did not show a cysteine (Cys) at position 5, in contrast to what has frequently been reported for nucleotide-based se quences of LMW-GS. This Cys has been replaced by one occurring in the repea ted-sequence domain, leaving the total number of Cys residues in the molecu le the same as in various other LMW-GS. On the basis of the deduced amino a cid sequence and literature-based assignment of disulfide linkages, a compu ter-generated molecular model of the 42K subunit was constructed.