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BIOCHEMICAL PROCESSES AND MACROMOLECULAR STRUCTURES

eEF1A Isoforms Change in Abundance and Actin-Binding Activity during Maize Endosperm Development¹

Department of Plant Sciences, University of Arizona, Tucson, Arizona 85721 (J.A.L.-V., B.C.G., P.A.H., B.A.L.); and Department of Agricultural Chemistry, Oregon State University, Corvallis, Oregon 97331–7301 (T.W.D.)

Eukaryotic elongation factor 1A (eEF1A) appears to be a multifunctional protein because several biochemical activities have been described for this protein, in addition to its role in protein synthesis. In maize (Zea mays) endosperm, the synthesis of eEF1A is increased in o2 (opaque2) mutants, and its concentration is highly correlated with the protein-bound lysine content. To understand the basis of this relationship, we purified eEF1A isoforms from developing endosperm and investigated their accumulation and their functional and structural properties. Formation of three isoforms appears to be developmentally regulated and independent of the o2 mutation, although one isoform predominated in one high lysine o2 inbred. The purified proteins differ in their ability to bind F-actin in vitro, suggesting that they are functionally distinct. However, they share similar aminoacyl-tRNA-binding activities. Tandem mass spectrometry revealed that each isoform is composed of the four same gene products, which are modified posttranslationally by methylation and phosphorylation. The chemical differences that account for their different actin-binding activities could not be determined.

¹ This work was supported by the U.S. Department of Agriculture National Research Initiative (grant no. NRI 981427 to B.A.L.), by the Department of Energy (grant no. DE–96ER20242 to B.A.L.), and by the Consejo Nacional de Ciencia y Tecnologia, Mexico (graduate fellowship to J.A.L.-V.).

² Present address: Commonwealth Scientific and Industrial Research Organization, Plant Industry, P.O. Box 1600, Canberra ACT 2601, Australia.

^* Corresponding author; e-mail larkins{at}ag.arizona.edu; fax 520–621–3692.

Received May 31, 2003; returned for revision July 7, 2003; accepted July 27, 2003.

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