Plant Physiol.
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Plant Physiology 76:16-20 (1984)
© 1984 American Society of Plant Biologists

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Articles

Intracellular Transport and Posttranslational Cleavage of Oat Globulin Precursors 1

Khosrow Adeli, Paula Allan-Wojtas and Illimar Altosaar

Department of Biochemistry, University of Ottawa, Ottawa, Ontario K1N 9B4 Canada, Food Research Institute, Agriculture Canada, Ottawa, Ontario K1A 0C5 Canada

The synthesis, transport, and posttranslational processing of reserve globulin in Avena sativa L. seeds were studied by pulse-chase labeling. Developing oat seeds were labeled with radioactive sulfate and tissue homogenates were used for globulin extraction.

Two globulin precursors (58-62 kilodaltons) were labeled after 1 hour pulse. The {alpha} and beta globulin subunits appeared between 2 and 10 hours later, while simultaneously the 58 to 62 kilodaltons polypeptides gradually disappeared. This confirmed a precursor-product relationship. In a second pulse-chase experiment, the tissue extracts were fractionated on a sucrose gradient. The major portion of radioactivity was initially (1 hour pulse) associated with the endoplasmic reticulum. However, a significant amount of radioactivity shifted from the endoplasmic reticulum to protein bodies after 20 hours chase, suggesting the transport of the newly synthesized proteins. Protein bodies isolated from pulse-chased seeds were analyzed for the arrival of the newly synthesized globulin. Labeled precursors were detected after 2 hours chase and gradually disappeared. The {alpha} and beta subunits appeared during the same chase period and assembled into a 12S oligomer.

The data indicated that oat globulin was synthesized as two large precursors which were transported from endoplasmic reticulum into protein bodies where they were processed to the {alpha} and beta subunits forming a 12S oligomer.

1 Supported in part by Natural Science and Engineering Research Council grant A6711 and Agriculture Canada Research Contract No. 0SU81-00411. Contribution 583 from the Food Research Institute, Agriculture Canada, Ottawa.






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