Role of structural domains for maize gamma-zein retention in Xenopus oocytes.

In order to examine the role of cysteine (Cys)-rich domains in the accumulation of maize (Zea mays L.) gamma-zein within the endoplasmic-reticulum-derived protein bodies, we studied the localization of gamma-zein and of two truncated forms of gamma-zein in Xenopus laevis oocytes. The two derivatives were constructed from a DNA encoding the gamma-zein: one by deletion of the Pro-X linker region (21 amino acids) and the other by deletion of the Cys-rich domain (94 amino acids). In-vitro-synthesized transcripts were injected into oocytes and the distribution of the translation products was then analyzed. The entire gamma-zein and both truncated forms of the gamma-zein had accumulated efficiently in microsomes and no traces of secretion were observed. We suggest that neither C-terminal Cys-rich nor Pro-X domains are essential for gamma-zein retention in oocyte vesicles. Therefore, structural features derived from disulphide bonds are not necessary for gamma-zein targeting on the endoplasmic reticulum.