PLANT PHYSIOLOGY , Vol 106, Issue 4 1413-1419, Copyright © 1994 by American Society of Plant Biologists
|
METABOLISM AND ENZYMOLOGY |
Identification of Posttranslationally Modified 18-Kilodalton Protein from Rice as Eukaryotic Translation Initiation Factor 5A
A. M. Mehta, R. A. Saftner, R. A. Mehta and P. J. Davies
Section of Plant Biology, Cornell University, Ithaca, New York 14853-5908 (A.M.M., P.J.D.)
Using anther-derived rice (Oryza sativa L.) cell-suspension cultures, we
have identified an 18-kD protein that is posttranslationally modified by
spermidine and is influenced by endogenous polyamine levels. The
posttranslationally modified residue has been identified as the unusual
amino acid hypusine [N[epsilon]-(4-amino-2-hydroxybutyl)lysine] by
reverse-phase high-performance liquid chromatography and gas
chromatography-mass-spectrometry analyses. Differential labeling of the
protein with labeled amines provided evidence that the butylamine moiety of
spermidine is the immediate precursor of the hypusine residue in the
protein. The eukaryotic translation initiation factor 5A (eIF-5A) is the
only known mammalian protein that undergoes a similar posttranslational
modification with hypusine. The purified 18-kD protein co-electrophoreses
with human translational initiation factor eIF-5A in both isoelectric
focusing and sodium dodecyl sulfate-polyacrylamide gels. The purified
protein from rice stimulated methionyl-puromycin synthesis in vitro,
indicating its functional similarity to mammalian eIF-5A. The results
presented provide evidence that the posttranslationally modified 18-kD
protein from rice containing hypusine is eIF-5A and suggest the
conservation of hypusine-containing translation initiation factor eIF-5A in
eukaryotes.
