Endoplasmic reticulum targeting and glycosylation of hybrid proteins in transgenic tobacco.

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Abstract
The correct compartmentation of proteins to the endomembrane system, mitochondria, or chloroplasts requires an amino-terminal signal peptide. The major tuber protein of potato, patatin, has a signal peptide in common with many other plant storage proteins. When the putative signal peptide of patatin was fused to the bacterial reporter protein .beta.-glucuronidase, the fusion proteins were translocated to the endoplasmic reticulum in planta and in vitro. In addition, translocated .beta.-glucuronidase was modified by glycosylation, and the signal peptide was correctly processed. In the presence of an inhibitor of glycosylation, tunicamycin, the enzymatically active form of .beta.-glucuronidase was assembled in the endoplasmic reticulum. This is the first report of targeting a cytoplasmic protein to the endoplasmic reticulum of plants using a signal peptide.