Deoxyhypusine Synthase Activity Is Essential for Cell Viability in the Yeast Saccharomyces cerevisiae

Abstract

Deoxyhypusine synthase catalyzes the first step in the posttranslational synthesis of an unusual amino acid, hypusine (N ε-(4-amino-2-hydroxybutyl)lysine), in the eukaryotic translation initiation factor 5A (eIF-5A) precursor protein. The null mutation in the single copy gene, yDHS, encoding deoxyhypusine synthase results in the loss of viability in the yeast Saccharomyces cerevisiae. Upon depletion of deoxyhypusine synthase, and consequently of eIF-5A, cessation of growth was accompanied by a marked enlargement of cells, suggesting a defect in cell cycle progression or in cell division. Two residues of the yeast enzyme, Lys308 and Lys350, corresponding to Lys287 and Lys329, respectively, known to be critical for the activity of the human enzyme, were targeted for site-directed mutagenesis. The chromosomal ydhs null mutation was complemented by the plasmid-borne yDHSwild-type gene, but not by mutated genes encoding inactive proteins, including that with Lys350 → Arg substitution or with substitutions at both Lys308 and Lys350. The mutated gene ydhs(K308R) encoding a protein with diminished activities (<1% of wild type) could support growth but only to a very limited extent. These findings provide strong evidence that the hypusine modification is indeed essential for the survival of S. cerevisiae and imply a vital function for eIF-5A in all eukaryotes. Deoxyhypusine synthase catalyzes the first step in the posttranslational synthesis of an unusual amino acid, hypusine (N ε-(4-amino-2-hydroxybutyl)lysine), in the eukaryotic translation initiation factor 5A (eIF-5A) precursor protein. The null mutation in the single copy gene, yDHS, encoding deoxyhypusine synthase results in the loss of viability in the yeast Saccharomyces cerevisiae. Upon depletion of deoxyhypusine synthase, and consequently of eIF-5A, cessation of growth was accompanied by a marked enlargement of cells, suggesting a defect in cell cycle progression or in cell division. Two residues of the yeast enzyme, Lys308 and Lys350, corresponding to Lys287 and Lys329, respectively, known to be critical for the activity of the human enzyme, were targeted for site-directed mutagenesis. The chromosomal ydhs null mutation was complemented by the plasmid-borne yDHSwild-type gene, but not by mutated genes encoding inactive proteins, including that with Lys350 → Arg substitution or with substitutions at both Lys308 and Lys350. The mutated gene ydhs(K308R) encoding a protein with diminished activities (<1% of wild type) could support growth but only to a very limited extent. These findings provide strong evidence that the hypusine modification is indeed essential for the survival of S. cerevisiae and imply a vital function for eIF-5A in all eukaryotes. The biosynthesis of the unusual amino acid, hypusine (N ε-(4-amino-2-hydroxybutyl)lysine), represents a novel posttranslational modification that occurs exclusively in one cellular protein, the precursor of eukaryotic translation initiation factor 5A (eIF-5A) 1The abbreviations used are: eIF-5A, eukaryotic translation initiation factor 5A (eIF-5A defines the fully modified protein containing hypusine; the unmodified protein containing lysine in place of hypusine is termed eIF-5A precursor); ORF, open reading frame; yDHS, yeast deoxyhypusine synthase; PCR, polymerase chain reaction; 5-FOA, 5-fluoroorotic acid; bp, base pair(s); kb, kilobase pair(s). (1Park M.H. Wolff E.C. Folk J.E. BioFactors. 1993; 4: 95-104PubMed Google Scholar, 2Park M.H Wolff E.C. Folk J.E. Trends Biochem. Sci. 1993; 18: 475-479Abstract Full Text PDF PubMed Scopus (145) Google Scholar). In the first step of hypusine synthesis, deoxyhypusine synthase catalyzes transfer of the butylamine moiety of the polyamine spermidine to the ε-amino group of a specific lysine residue of eIF-5A precursor (Lys51 in the yeast proteins) to form a deoxyhypusine (N ε-(4-aminobutyl)lysine) residue (3Park M.H. Cooper H.L. Folk J.E. J. Biol. Chem. 1982; 257: 7217-7222Abstract Full Text PDF PubMed Google Scholar,4Wolff E.C. Lee Y.B. Chung S.I. Folk J.E. Park M.H. J. Biol. Chem. 1995; 270: 8660-8666Abstract Full Text Full Text PDF PubMed Scopus (53) Google Scholar). Hydroxylation of the side chain of this intermediate by deoxyhypusine hydroxylase completes hypusine biosynthesis and eIF-5A maturation (5Abbruzzese A. Park M.H. Folk J.E. J. Biol. Chem. 1986; 261: 3085-3089Abstract Full Text PDF PubMed Google Scholar). Deoxyhypusine synthase has been purified from rat testis (4Wolff E.C. Lee Y.B. Chung S.I. Folk J.E. Park M.H. J. Biol. Chem. 1995; 270: 8660-8666Abstract Full Text Full Text PDF PubMed Scopus (53) Google Scholar),Neurospora crassa (6Tao Y. Chen K.Y. J. Biol. Chem. 1995; 270: 23984-23987Abstract Full Text Full Text PDF PubMed Scopus (27) Google Scholar), HeLa cells (7Klier H. Csonga R. Steinkasser A. Wöhl T. Lottspeich F. Eder J. FEBS Lett. 1995; 364: 207-210Crossref PubMed Scopus (22) Google Scholar), and yeast (8Sasaki K. Abid M.R. Miyazaki M. FEBS Lett. 1996; 384: 151-154Crossref PubMed Scopus (113) Google Scholar). Human (9Joe Y.A. Wolff E.C. Park M.H. J. Biol. Chem. 1995; 270: 22386-22392Abstract Full Text Full Text PDF PubMed Scopus (76) Google Scholar, 10Tao Y. Chen K.Y. Biochem. J. 1996; 315: 429-434Crossref PubMed Scopus (21) Google Scholar) and N. crassa (11Tao Y. Chen K.Y. J. Biol. Chem. 1995; 270: 383-386Abstract Full Text Full Text PDF PubMed Scopus (30) Google Scholar) cDNAs for the enzyme have been cloned, and its gene has been identified (7Klier H. Csonga R. Steinkasser A. Wöhl T. Lottspeich F. Eder J. FEBS Lett. 1995; 364: 207-210Crossref PubMed Scopus (22) Google Scholar, 11Tao Y. Chen K.Y. J. Biol. Chem. 1995; 270: 383-386Abstract Full Text Full Text PDF PubMed Scopus (30) Google Scholar, 12Kang K.R. Wolff E.C. Park M.H. Folk J.E. Chung S.I. J. Biol. Chem. 1995; 270: 18408-18412Abstract Full Text Full Text PDF PubMed Scopus (42) Google Scholar) and cloned (8Sasaki K. Abid M.R. Miyazaki M. FEBS Lett. 1996; 384: 151-154Crossref PubMed Scopus (113) Google Scholar) in yeast. The amino acid sequence of deoxyhypusine synthase is highly conserved and enzymes from different species exist as homotetramers of 40 to 43-kDa subunits. In recent studies with human deoxyhypusine synthase, we have identified an active site lysine residue, Lys329, that is involved in enzyme-substrate intermediate formation (13Wolff E.C. Folk J.E. Park M.H. J. Biol. Chem. 1997; 272: 15865-15871Abstract Full Text Full Text PDF PubMed Scopus (40) Google Scholar). Replacement of all the conserved lysine residues of the human enzyme (with Lys → Arg or Lys → Ala) by site-directed mutagenesis revealed that Lys329 and Lys287 are critical for enzyme activity (43Joe Y.A. Wolff E.C. Lee Y.B. Park M.H. J. Biol. Chem. 1997; 272: 32679-32685Abstract Full Text Full Text PDF PubMed Scopus (19) Google Scholar). Hypusine is ubiquitous in eukaryotes, occurring at one highly conserved residue of eIF-5A. The assignment of this protein as a putative translation initiation factor was based on its in vitroability to stimulate methionyl puromycin synthesis (14Kemper W.M. Berry K.W. Merrick W.C. J. Biol. Chem. 1976; 251: 5551-5557Abstract Full Text PDF PubMed Google Scholar). However, its true physiological function is as yet unknown. An increasing body of evidence supports the notion that eIF-5A and its hypusine modification play a pivotal role in eukaryotic cell proliferation (1Park M.H. Wolff E.C. Folk J.E. BioFactors. 1993; 4: 95-104PubMed Google Scholar, 2Park M.H Wolff E.C. Folk J.E. Trends Biochem. Sci. 1993; 18: 475-479Abstract Full Text PDF PubMed Scopus (145) Google Scholar). In mammalian cells, inhibitors of either deoxyhypusine synthase (15Park M.H. Wolff E.C. Lee Y.B. Folk J.E. J. Biol. Chem. 1994; 269: 27827-27832Abstract Full Text PDF PubMed Google Scholar) or deoxyhypusine hydroxylase (16Hanauske-Abel H.M. Park M.H. Hanauske A.-R. Popowicz A.M. Lalande M. Folk J.E. Biochim. Biophys. Acta. 1994; 1221: 115-124Crossref PubMed Scopus (132) Google Scholar) exert anti-proliferative effects. The arrest in cell proliferation by inhibitors of polyamine biosynthetic enzymes has been attributed to depletion of eIF-5A following deprivation of spermidine (17Byers T.L. Ganem B. Pegg A.E. Biochem. J. 1992; 287: 717-724Crossref PubMed Scopus (79) Google Scholar). The ability of spermidine analogues to support the growth of polyamine-deficient cells correlated with their competency to act as a substrate for deoxyhypusine synthesis (17Byers T.L. Ganem B. Pegg A.E. Biochem. J. 1992; 287: 717-724Crossref PubMed Scopus (79) Google Scholar, 18Byers T.L. Lakanen J.R. Coward J.K. Pegg A.E. Biochem. J. 1994; 303: 363-368Crossref PubMed Scopus (69) Google Scholar). Schnier et al. (19Schnier J. Schwelberger H. Smit-McBride Z. Kang H.A. Hershey J.W.B. Mol. Cell. Biol. 1991; 11: 3105-3114Crossref PubMed Scopus (289) Google Scholar) and Wöhl et al. (20Wöhl T. Klier H. Ammer H. Lottspeich F. Magdolen V. Mol. Gen. Genet. 1993; 241: 305-311Crossref PubMed Scopus (61) Google Scholar) independently demonstrated that expression of either one of the two eIF-5A genes in the yeast Saccharomyces cerevisiae is vital for yeast survival. Schnier et al. further showed that a yeast mutant protein, eIF-5A precursor(K51R), which cannot be modified to the hypusine form due to the substitution of Arg51 for Lys, did not support the growth of yeast. Although suggesting the importance of the preservation of Lys51 for hypusine synthesis, these results do not provide direct evidence of the essential requirement of the hypusine modification for yeast growth. We undertook a study to determine the role of deoxyhypusine synthase in the yeast S. cerevisiae through inactivation of its gene. Our data as well as those of Sasaki et al. (8Sasaki K. Abid M.R. Miyazaki M. FEBS Lett. 1996; 384: 151-154Crossref PubMed Scopus (113) Google Scholar), recently reported while this work was in progress, indicate that this gene is essential for cell viability in yeast. We extended the yDHSgene disruption studies by employing site-directed mutagenesis and plasmid shuffle techniques to compare the capabilities of wild type and mutated yDHS genes to support yeast growth. Single or double mutations were introduced into yDHS at the sites encoding Lys308 and Lys350 (corresponding to Lys287 and Lys329, respectively, of the human enzyme). Our results presented here show that the activity of deoxyhypusine synthase, as well as the gene product, is required for yeast viability and thus provide strong evidence of an essential role for eIF-5A and its hypusine modification in eukaryotic cell proliferation. Furthermore, the marked increase in the size of the cells at the cessation of growth upon depletion of deoxyhypusine synthase, and consequently of eIF-5A, invites speculation on the possible role of eIF-5A in the cell division phase of the cell cycle. The genotypes and sources of theS. cerevisiae strains used in this work are listed in TableI. S. cerevisiae strain JS10 (19Schnier J. Schwelberger H. Smit-McBride Z. Kang H.A. Hershey J.W.B. Mol. Cell. Biol. 1991; 11: 3105-3114Crossref PubMed Scopus (289) Google Scholar), plasmid YEp13 (21Broach J.R. Strathern J.N. Hicks J.B. Gene (Amst.). 1979; 8: 121-133Crossref PubMed Scopus (672) Google Scholar), and plasmid YEp352 (22Hill J.E. Myers A.M. Koerner T.J. Tzagloff A. Yeast. 1986; 2: 163-167Crossref PubMed Scopus (1083) Google Scholar) were kindly supplied by Dr. John W. B. Hershey (University of California, Davis, CA). Plasmid pRS316 (23Sikorski R.S. Hieter P. Genetics. 1989; 122: 19-27Crossref PubMed Google Scholar) was a generous gift from Drs. Nobuko Hamasaki, Celia Tabor, and Herbert Tabor (NIDDK, National Institutes of Health, Bethesda, MD), and plasmid pJJ246 (24Jones J.S. Prakashi L. Yeast. 1990; 6: 363-366Crossref PubMed Scopus (327) Google Scholar) from Dr. Reed Wickner (NIDDK, National Institutes of Plasmid K. S. Sci. S. A. 1979; Scopus Google Scholar) was from MD), and plasmid from Plasmid was by from pJJ246 into the site of YEp352 by strains and or or the of its JS10 and its including all those listed in this to be the specific for the is W. B. Hershey (19Schnier J. Schwelberger H. Smit-McBride Z. Kang H.A. Hershey J.W.B. Mol. Cell. Biol. 1991; 11: 3105-3114Crossref PubMed Scopus (289) Google Scholar) work work work work work work work work work work of work J.E. Myers A.M. Koerner T.J. Tzagloff A. Yeast. 1986; 2: 163-167Crossref PubMed Scopus (1083) Google work work K. S. Sci. S. A. 1979; Scopus Google work work work work work the of its JS10 and its including all those listed in this to be the specific for the is of in a the open reading of yeast deoxyhypusine synthase gene with sites the and was by yeast as a and a of and with the was into the site of to was with to a from the of this a gene from YEp13 by with and was by in with yDHS by was of with and was used for of S. cerevisiae strain JS10 the Scholar). were from sequence of used in in indicate the of the or of yeast deoxyhypusine synthase gene based on the sequence of these are in are to enzyme sites are of that are and indicate mutated in a The in indicate the of the or of yeast deoxyhypusine synthase gene based on the sequence of these are in are to enzyme sites are of that are and indicate mutated The yDHS gene with and sites introduced at the and respectively, of the was as in B. with and and with were by of the cerevisiae strain JS10 the and at the and the of are the two purified from a were used as for the of with the to a with and this was into site of to was with and and with the yDHS ORF, from K.R. Wolff E.C. Park M.H. Folk J.E. Chung S.I. J. Biol. Chem. 1995; 270: 18408-18412Abstract Full Text Full Text PDF PubMed Scopus (42) Google Scholar), to The from was into site of the plasmid pRS316 to form or into the site of the yeast plasmid to of and was to site of to the of mutant enzymes in the of the containing wild type yDHS gene was with a of mutated yDHS mutations at Lys308 and Lys350 were by mutagenesis Z. 1990; 8: Google Scholar). The Lys corresponding to amino acid residue or was by the Arg or In the first of Lys308 with Arg was containing the Arg in place of the Lys Two in the first of PCR, as the and the and were and in the of the to a of the mutation was in a with as the and targeted to Lys350 to or The yDHS or yDHS single mutation was the site-directed mutagenesis with as the for Lys308 to Arg substitution and for Lys350 to Arg The of the mutation was by of the mutated into a We and identified in S. cerevisiae as a gene for yeast deoxyhypusine synthase by for in the data base that the amino acid for the enzymes from rat (4Wolff E.C. Lee Y.B. Chung S.I. Folk J.E. Park M.H. J. Biol. Chem. 1995; 270: 8660-8666Abstract Full Text Full Text PDF PubMed Scopus (53) Google Scholar), human (7Klier H. Csonga R. Steinkasser A. Wöhl T. Lottspeich F. Eder J. FEBS Lett. 1995; 364: 207-210Crossref PubMed Scopus (22) Google Scholar), or N. crassa (11Tao Y. Chen K.Y. J. Biol. Chem. 1995; 270: 383-386Abstract Full Text Full Text PDF PubMed Scopus (30) Google Scholar). The of the deoxyhypusine synthase gene was by activity expression of its in K.R. Wolff E.C. Park M.H. Folk J.E. Chung S.I. J. Biol. Chem. 1995; 270: 18408-18412Abstract Full Text Full Text PDF PubMed Scopus (42) Google Scholar). Sasaki et deoxyhypusine synthase from yeast and cloned the gene (8Sasaki K. Abid M.R. Miyazaki M. FEBS Lett. 1996; 384: 151-154Crossref PubMed Scopus (113) Google Scholar). to be a single gene for this enzyme in yeast. of yeast with with the of one in of or kb, not Furthermore, sequence to the of yDHS is in the of S. cerevisiae A. H. B. H. F. M. Y. P. H. 1996; PubMed Scopus Google Scholar), by the of for determine the deoxyhypusine synthase gene is essential for cell viability in we a with the of the and with as in A. with yDHS was used to the JS10 were disruption of chromosomal was by in yDHS on one and a on the in the of growth and of JS10 and of the was suggesting that disruption of one chromosomal is not in yeast was to by two of the from to of were was an that the with the is not of those to form revealed that did in but to or open of the ydhs null mutant showed growth cells, or wild type cells, or the the yDHS to and on on In cell division by at a size of cells of size is that from to a marked increase in cell size with in further increase in cell or size was upon to In the of the yDHS cells, enlargement was on The arrest in growth of null cell results from depletion of deoxyhypusine synthase and consequently a in eIF-5A the required to support cell of and and growth of and ydhs null strain or with was and on a were to their growth. of yDHS and ydhs null is null showed a growth arrest to that of the one The data of and show that the ydhs null mutation on the with the plasmid and yDHS, or a copy plasmid was and were the of from either plasmid could two of from as from to a of from were all from were the of growth on the yDHS gene on the that did not form growth cell to those in from and of were containing or of the were with chromosomal yDHS and the with chromosomal the were containing and 5-FOA, which only cells that the In could on suggesting that cannot yDHS from the evidence for the of the ydhs null on plasmid-borne yDHS for growth was from of plasmid of the and the both and of in of the two strains in loss of the for containing but of loss of the plasmid was for the the suggesting the of yDHS for yeast survival. We the of the role of gene in cell growth to provide deoxyhypusine synthesis activity and hypusine modification in eIF-5A. mutated yDHS we to a the deoxyhypusine synthesis activity of the mutant and their ability to support growth in yeast. two lysine residues and Lys329 of the human have been identified as critical for deoxyhypusine synthase activity (13Wolff E.C. Folk J.E. Park M.H. J. Biol. Chem. 1997; 272: 15865-15871Abstract Full Text Full Text PDF PubMed Scopus (40) Google Scholar, Y.A. Wolff E.C. Lee Y.B. Park M.H. J. Biol. Chem. 1997; 272: 32679-32685Abstract Full Text Full Text PDF PubMed Scopus (19) Google Scholar), we targeted the two corresponding residues in the yeast enzyme and Lys350, for The expression of the mutant with mutations at Lys308 Lys350 were in cells Deoxyhypusine synthase activity of mutant protein was its substrate proteins, the human eIF-5A and the two yeast eIF-5A and The mutant protein but activity of the wild type enzyme the two yeast eIF-5A precursor proteins, but not with the human precursor protein. activity was with or with the double mutant proteins, and with of the substrate proteins, that Lys350 a critical role in The mutated genes or the wild type gene were into the plasmid of the with the containing both were and for their growth on for cells that have the only in the growth was for the containing encoding the was of growth for those containing encoding inactive or of the double mutant growth was the with the of wild type and genes for their ability to support the growth of yeast. The strain was with plasmid either the wild type or one of mutant were from were on with and of the was at for were the for the of growth was for those the or of the mutated to The study evidence that deoxyhypusine synthesis activity is vital for growth of the yeast S. cerevisiae. The yDHS gene disruption presented here and in an (8Sasaki K. Abid M.R. Miyazaki M. FEBS Lett. 1996; 384: 151-154Crossref PubMed Scopus (113) Google Scholar) the eIF-5A gene inactivation studies in yeast (19Schnier J. Schwelberger H. Smit-McBride Z. Kang H.A. Hershey J.W.B. Mol. Cell. Biol. 1991; 11: 3105-3114Crossref PubMed Scopus (289) Google Scholar, T. Klier H. Ammer H. Lottspeich F. Magdolen V. Mol. Gen. Genet. 1993; 241: 305-311Crossref PubMed Scopus (61) Google Scholar). the of human and yeast Kang H.A. Hershey J.W.B. J. Biol. Chem. 1993; Full Text PDF PubMed Google Scholar), and the sequence of eIF-5A (1Park M.H. Wolff E.C. Folk J.E. BioFactors. 1993; 4: 95-104PubMed Google Scholar), these results to the that both the expression of eIF-5A precursor protein and its hypusine modification are required for proliferation of all eukaryotes. Although Sasaki et al. (8Sasaki K. Abid M.R. Miyazaki M. FEBS Lett. 1996; 384: 151-154Crossref PubMed Scopus (113) Google Scholar) recently reported evidence that the yDHS gene is essential for viability of S. the could not be that the yDHS gene or its protein, in to deoxyhypusine synthesis have an function vital for yeast yeast growth on deoxyhypusine synthase we mutations at Lys308 and Lys350 of the those the enzyme, growth was for the cells the mutated or that mutant that are inactive in deoxyhypusine growth was with that a enzyme with of the enzyme The loss of growth and of enzyme activities that the in the of the mutant is to loss of deoxyhypusine synthesis human deoxyhypusine synthase, which sequence and with the yeast enzyme, been identified as the active site residue involved in the enzyme-substrate intermediate formation (13Wolff E.C. Folk J.E. Park M.H. J. Biol. Chem. 1997; 272: 15865-15871Abstract Full Text Full Text PDF PubMed Scopus (40) Google Scholar), and to be critical residue the active site (43Joe Y.A. Wolff E.C. Lee Y.B. Park M.H. J. Biol. Chem. 1997; 272: 32679-32685Abstract Full Text Full Text PDF PubMed Scopus (19) Google Scholar). The mutant of the human enzyme and to the ability to form (43Joe Y.A. Wolff E.C. Lee Y.B. Park M.H. J. Biol. Chem. 1997; 272: 32679-32685Abstract Full Text Full Text PDF PubMed Scopus (19) Google Scholar). to that in the yeast mutant and is disruption of or of the active from the of deoxyhypusine activity of the yeast enzyme, the corresponding lysine residue of the human enzyme, to be essential for as the site of enzyme-substrate intermediate Wolff and M. H. eIF-5A is the only protein known to eIF-5A is an protein with a Hershey J.W.B. J. Biol. Chem. 1986; 261: Full Text PDF PubMed Google Scholar), the of deoxyhypusine synthase in the ydhs null mutant be to in the depletion of only this eIF-5A, with the of the eIF-5A precursor protein. eIF-5A precursor to be a protein in cells, for its was in yeast the eIF-5A gene from a plasmid T. Klier H. Lottspeich F. 1995; PubMed Scopus Google Scholar). The growth of ydhs null from as deoxyhypusine synthase and eIF-5A from the due to and through cell In the of disruption of the eIF-5A gene null from to of growth (20Wöhl T. Klier H. Ammer H. Lottspeich F. Magdolen V. Mol. Gen. Genet. 1993; 241: 305-311Crossref PubMed Scopus (61) Google Scholar). The that null for a null the required for the depletion of deoxyhypusine synthase the in eIF-5A from this required for enzyme and the of of eIF-5A precursor protein in cells Hershey J.W.B. J. Biol. Chem. 1986; 261: Full Text PDF PubMed Google Scholar), is that deoxyhypusine synthase is a protein in the to all the eIF-5A precursor the that the mutant with enzyme activity of the enzyme, support at a The arrest of growth of ydhs null with cells with that cessation of growth upon deprivation of deoxyhypusine synthase is by specific in cell cycle progression or division. growth arrest was accompanied by a enlargement of cells in the S. cerevisiae strain upon depletion of a but eIF-5A protein, H.A. Hershey J.W.B. J. Biol. Chem. 1994; 269: Full Text PDF PubMed Google Scholar). is to that in both the cessation of growth is by cellular from of eIF-5A. increase in cell size was in cells growth was following depletion of the spermidine and in a S. cerevisiae strain with a null mutation of the gene Tabor Tabor H. Sci. S. A. 1991; PubMed Scopus Google Scholar). In to in of and of and were Tabor Tabor H. Sci. S. A. 1991; PubMed Scopus Google Scholar). These are to the reported for a cell division cycle mutant J.R. PubMed Scopus Google Scholar, J. PubMed Google Scholar). cells physiological including loss of Tabor Tabor H. Sci. S. A. 1993; PubMed Scopus Google Scholar), increase in Wickner Tabor Tabor H. Sci. S. A. 1994; PubMed Scopus Google Scholar), and to by Tabor Tabor H. Sci. S. A. 1993; PubMed Scopus Google Scholar) and Tabor Tabor H. J. 1996; PubMed Google Scholar). Although hypusine has been as a of the polyamine requirement in eukaryotic cells (20Wöhl T. Klier H. Ammer H. Lottspeich F. Magdolen V. Mol. Gen. Genet. 1993; 241: 305-311Crossref PubMed Scopus (61) Google Scholar), is not known which of these cellular are by eIF-5A the essential of hypusine and eIF-5A in cell the true physiological function of eIF-5A an In a depletion of eIF-5A was in only a in protein synthesis and a in were H.A. Hershey J.W.B. J. Biol. Chem. 1994; 269: Full Text PDF PubMed Google Scholar). to the that eIF-5A is not a protein synthesis initiation factor but that act as a factor for a of specific In with this is the that inhibitors of deoxyhypusine the enzyme that catalyzes the step of hypusine synthesis, arrest of mammalian cells at the of the cell cycle (16Hanauske-Abel H.M. Park M.H. Hanauske A.-R. Popowicz A.M. Lalande M. Folk J.E. Biochim. Biophys. Acta. 1994; 1221: 115-124Crossref PubMed Scopus (132) Google Scholar). eIF-5A was reported to be a cellular essential for function in human type M. M. F. H. Wolff B. H. H. J. J. Cell. Biol. 1993; PubMed Scopus Google Scholar) or function in human J. T. H. A. K. H. J. 1995; PubMed Google Scholar), thus speculation on its role in the and of specific The that yeast cells of and those of eIF-5A or of deoxyhypusine synthase a enlargement the that eIF-5A play a role in cell division cycle eIF-5A be either involved in this or function by the expression of a of critical for cell division. and of the that in eIF-5A cells further on the physiological function of this protein. We are to Dr. Nobuko for in for of and for