**5.3 Prolamins**

About 20% -30% seed protein is comprised of prolamins. Multigerne family of 34 gene copies having relative molecular weights −10, 13, and 16 kD encoding the prolamin proteins. Among them the 13 kD molecular weight gene family comprises the major group. Further, on the basis of abundance of cysteine residues the 13 kD prolamins are classified in class I, II, or III, [56, 57]. Prolamins are the main storage proteins in the endosperm of all cereal grains. These proteins are basically rich in proline and amide nitrogen which is derivative of glutamine. The prolamins contains variable molecular masses ranging from approx 10 000 to 100 000. Miflin et al. [58], on the basis of amino acid sequencing, classified the prolamins into three groups namely S-rich, S-poor, and high molecular weight (HMW) prolamins. Among them S-rich prolamins are found to be about 80 to 90% of the total prolamin fractions consisting of monomeric and polymeric components with intrachain and interchain disulfide bonds respectively. The most abundant prolamin group among rice storage proteins is 13 kD prolamins that is indigestible in nature (Hyun-Jung [59]). Kim et al. [59] have generated transgenic rice plants (13 kD pro-RNAi) consisting of RNAi that are constructing against 13 kD prolamins. They reported in their results that 28% increase in the level of lysine, and abnormal formation of PB-I (protein bodies) in the transgenic grains might be due to the reduction in 13 kD prolamins at the mRNA and protein levels.
