Dimerization of the yeast eukaryotic translation initiation factor 5A requires hypusine and is RNA dependent

Post-translational modification of the highly conserved K51 residue of the Saccharomyces cerevisiae eukaryotic translation initiation factor 5A (eIF5A) to form hypusine, is essential for its many functions including the binding of specific mRNAs. We characterized hypusinated yeast eIF5A by size-exclusion chromatography and native PAGE, showing that the protein exists as a homodimer. A K51R mutant, which was not functional in vivo eluted as a monomer and inhibition of hypusination abolished dimerization. Furthermore, treatment of dimeric eIF5A with RNase A resulted in disruption of the dimer, leading us to conclude that RNA binding is also required for dimerization of eIF5A. We present a model of dimerization, based on the Neurospora crassa structural analogue, HEX-1.