title: Pumpkin eIF5A isoforms interact with components of the translational machinery in the cucurbit sieve tube system.
abstract: In yeast, eIF5A, in combination with eEF2, functions at the translation step, during the protein elongation cycle. This result is of significance with respect to functioning of the enucleate sieve tube system, as eIF5A was recently detected in Cucurbita maxima (pumpkin) phloem sap. In the present study, we further characterized four CmeIF5A isoforms, encoding three proteins, all of which were present in the phloem sap. Although hypusination of CmeIF5A was not necessary for entry into the sieve elements, this unique post-translational modification was necessary for RNA binding. The two enzymes required for hypusination were detected in pumpkin phloem sap, where presumably this modification takes place. A combination of gel-filtration chromatography and protein overlay assays demonstrated that, as in yeast, CmeIF5A interacts with phloem proteins, like eEF2, known to be involved in protein synthesis. These findings are discussed in terms of a potential role for eIF5A in regulating protein synthesis within the enucleate sieve tube system of the angiosperms.
authors.affiliation: Department of Plant Biology, College of Biological Sciences, University of California, Davis, CA 95616, USA.
authors.forename: Yi
authors.initials: Y
authors.lastname: Ma
authors.forename: Eriko
authors.initials: E
authors.lastname: Miura
authors.forename: Byung-Kook
authors.initials: BK
authors.lastname: Ham
authors.forename: Hao-Wen
authors.initials: HW
authors.lastname: Cheng
authors.forename: Young-Jin
authors.initials: YJ
authors.lastname: Lee
authors.forename: William J
authors.initials: WJ
authors.lastname: Lucas
mesh_terms: D000595:Amino Acid Sequence; D017124:Conserved Sequence; D028464:Cucurbita / Q000235:genetics* / Q000378:metabolism; D008969:Molecular Sequence Data; D010448:Peptide Initiation Factors / Q000235:genetics / Q000378:metabolism*; D052585:Phloem / Q000378:metabolism*; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism*; D014176:Protein Biosynthesis; D020033:Protein Isoforms / Q000235:genetics / Q000378:metabolism; D011499:Protein Processing, Post-Translational; D016601:RNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D000097574:Eukaryotic Translation Initiation Factor 5A
chemical_list: D010448:Peptide Initiation Factors; D010940:Plant Proteins; D020033:Protein Isoforms; D016601:RNA-Binding Proteins; D000097574:Eukaryotic Translation Initiation Factor 5A