Molecular Cloning and Characterization of a Cysteine-rich 16.6-kDa Prolamin in Rice Seeds

An alcohol-soluble storage protein, a 16.6-kDa prolamin found in rice seeds, was purified from both the total protein body and purified type I protein body fractions. The partial amino acid sequences of three tryptic peptides generated from the purified polypeptide were analyzed. A part of the 16.6-kDa prolamin cDNA was amplified from developing seed mRNA by the reverse transcribed polymerase chain reaction using an oligo (dT) primer and a primer which was synthesized based on the partial amino acid sequence. The amplified product was used to isolate the full-length cDNA clone (lambda RP16) from a developing seed cDNA library. The cDNA has an open reading frame encoding a hydrophobic polypeptide of 149 amino acids. The polypeptide was rich in glutamine (20.0%), cysteine (10.0%), and methionine (6.9%). The cysteine content was higher than those of most other rice storage proteins. Messenger RNA of the 16.6-kDa prolamin was detected in seeds, but not in other aerial tissues.