Ricin B chain targeted to the endoplasmic reticulum of tobacco protoplasts is degraded by a CDC48- and vacuole-independent mechanism

The B chain of ricin (RTB) was expressed and delivered to the endoplasmic reticulum (ER) of tobacco protoplasts from where it disappeared with time in a manner consistent with degradation. This turnover did not occur in the vacuoles, or upon secretion. Indeed, several lines of evidence indicate that, in contrast to the turnover of ER-targeted ricin A chain (RTA) in the cytosol, the bulk of expressed RTB was degraded in the secretory pathway.