Zeins, the major seed storage proteins of maize, are of four distinct types: (Y, p, S, and y. They are synthesized on the rough endoplasmic reticulum (ER) in a sequential manner and deposited in ER-derived protein bodies. We investigated the potential for producing sulfur-rich p-zein and 6-zein proteins in leaf and seed tissues by expressing the corresponding genes in a constitutive manner in transgenic tobacco. The 6-zein and @-zein, when synthesized individually, were stable in the vegetative tissues and were deposited in unique, zein-specific ER-derived protein bodies. Coexpression of 6-zein and p-zein genes, however, showed that 6-zein was colocalized in p-zein-containing protein bodies and that the leve1 of 6-zein was fivefold higher in 6-/@-zein plants than in S-zein plants. We conclude that 6-zein interacts with p-rein and that the interaction has a stabilizing effect on 6-zein.