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Evidence for a Cytoskeleton-Associated Binding Site Involved in Prolamine mRNA Localization to the Protein Bodies in Rice Endosperm Tissue1
Institute of Biological Chemistry, Washington State University, Pullman, Washington 99164-6340 (D.G.M., Y.W., T.W.O.); and Pioneer Hi-Bred International, Johnston, Iowa 50131-1004 (S.J.C.) Previous studies have demonstrated that the mRNAs encoding the prolamine and glutelin storage proteins are localized to morphologically distinct membranes of the endoplasmic reticulum (ER) complex in developing rice (Oryza sativa L.) endosperm cells. To gain insight about this mRNA localization process, we investigated the association of prolamine polysomes on the ER that delimit the prolamine protein bodies (PBs). The bulk of the prolamine polysomes were resistant to extraction by 1% Triton X-100 either alone or together with puromycin, which suggests that these translation complexes are anchored to the PB surface through a second binding site in addition to the well-characterized ribosome-binding site of the ER-localized protein translocation complex. Suppression of translation initiation shows that these polysomes are bound through the mRNA, as shown by the simultaneous increase in the amounts of ribosome-free prolamine mRNAs and decrease in prolamine polysome content associated with the membrane-stripped PB fraction. The prolamine polysome-binding activity is likely to be associated with the cytoskeleton, based on the association of actin and tubulin with the prolamine polysomes and PBs after sucrose-density centrifugation. 1 This work was supported by U.S. Department of Agriculture National Research Initiative Competitive Grants Program Award no. 94-37304-1174 to T.W.O. 2 D.G.M. and Y.W. contributed equally to this publication. 3 Present address: Department of Biological Sciences, 2500 University Drive N.W., University of Calgary, Calgary, AB, Canada, T2N 1N4. * Corresponding author; e-mail tokita{at}wsu.edu; fax 1-509-335-7643.
Plant Physiol. (1998) 116: 559-569
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