The archaebacterial hypusine‐containing protein

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Abstract
The amino acid hypusine is formed by post‐translational modification of a lysine residue in eukaryotes and archaebacteria but up to now only the eukaryotic translation initiation factor eIF‐5A has been known to contain this unique component. We isolated and purified a hypusine‐containing protein from the thermophilic archaebacterium Sulfolobus acidocaldarius. The mainly cytosolic protein comprised about 0.03% of the post‐ribosomal supernatant protein. No other hypusine‐containing protein could be detected in S. acidocaldarius. The molar ratio of hypusine/hypusine‐containing protein was 1:1. SDS/PAGE showed a molecular mass of 16.8 kDa; a pI of 7.8 for the native protein resulted from IEF. The N‐terminus was blocked. Four cyanogen bromide fragments were partially sequenced and used to derive two 17‐base oligonucleotide probes. A 3‐kb HindIII fragment of genomic DNA hybridizing with both probes was cloned. By sequencing of exonuclease III deletion clones an open reading frame of 405 nucleotides was found coding for a protein of 135 amino acids with a molecular mass of 15 kDa. It contained all cyanogen bromide sequences analysed. Sequence alignment revealed that seven of eight residues around Lys40 in the Sulfolobus hypusine‐containing protein were identical to the nonapeptides centered by hypusine in the three eIF‐5A proteins sequenced so far. The Edman procedure gave no phenylthiohydantoin derivative for this position. For a central region of 44 residues a sequence similarity of 54% between the archaebacterial and eukaryotic proteins was calculated; for the total sequence about 33% similarity resulted. In addition, there were a number of conservative changes. The unique lysine modification surrounded by a conserved sequence strongly suggests a common ancestry of archaebacterial hypusine‐containing protein and eIF‐5A. Together with similarities in molecular mass and intracellular localization, it may point to an analogous biochemical function.

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