PLANT PHYSIOLOGY , Vol 115, Issue 3 1101-1107, Copyright © 1997 by American Society of Plant Biologists
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BIOCHEMISTRY AND ENZYMOLOGY |
Characterization of Maize Elongation Factor 1A and Its Relationship to Protein Quality in the Endosperm
Y. Sun, N. Carneiro, A. M. Clore, G. L. Moro, J. E. Habben and B. A. Larkins
Department of Plant Sciences, University of Arizona, Tucson, Arizona 85721
The protein synthesis elongation factor 1A (eEF1A) is a multifunctional
protein in eukaryotic cells. In maize (Zea mays L.) endosperm eEF1A
co-localizes with actin around protein bodies, and its accumulation is
highly correlated with the protein-bound lysine (Lys) content. We purified
eEF1A from maize kernels by ammonium sulfate precipitation, ion-exchange,
and chromatofocusing. The identity of the purified protein was confirmed by
microsequencing of an endoproteinase glutamic acid-C fragment and by its
ability to bundle actin. Using purified eEF1A as a standard, we found that
this protein contributes 0.4% of the total protein in W64A+ endosperm and
approximately 1% of the protein in W64Ao2. Because eEF1A contains 10% Lys,
it accounts for 2.2% of the total Lys in W64A+ and 2.3% of the Lys in
W64Ao2. However, its concentration predicts 90% of the Lys found in
endosperm proteins of both genotypes, indicating that eEF1A is a key
component of the group of proteins that determines the nutritional quality
of the grain. This notion is further supported by the fact that in floury2,
another high-Lys mutant, the content of eEF1A increases with the dosage of
the floury2 gene. These data provide the biochemical basis for further
investigation of the relationship between eEF1A content and the nutritional
quality of cereals.
