Cloning and characterization of a cDNA encoding a sulfur-rich coixin.

A full-length cDNA clone encoding a sulfur-rich Coix prolamin was isolated using a cDNA library constructed from polysomal mRNA prepared from immature Coix endosperm. The deduced amino acid sequence of the cDNA clone predicted a polypeptide of 194 residues, which shared 64% homology with the 17 kDa beta-zein. The mature protein contains the familiar composition of the prolamins and an unusually high content of the sulfur-containing amino acids methionine (11.6%) and cysteine (5.2%). In vitro transcription followed by in vitro translation of the coding region of the pBCX17.9S clone gave rise to a polypeptide with an apparent molecular weight corresponding to the C4 alpha-coixin. Hydropathy analysis showed that C4 alpha-coixin is slightly more hydrophobic than beta-zein.