Advertisement

Cloning and Heterologous Expression of an α1,3-Fucosyltransferase Gene from the Gastric PathogenHelicobacter pylori *

  • Zhongming Ge
    Affiliations
    Search for articles by this author
  • Nora W.C. Chan
    Affiliations
    Search for articles by this author
  • Monica M. Palcic
    Affiliations
    Search for articles by this author
  • Diane E. Taylor
    Correspondence
    Recipient of a Medical Scientist Award from the Alberta Heritage Foundation for Medical Research. To whom correspondence should be addressed: Dept. of Medical Microbiology and Immunology, 1–28 Medical Sciences Bldg., University of Alberta, Edmonton, Alberta, Canada T6G 2H7. Tel.: 403-492-4777; Fax: 403-492-7521
    Affiliations
    Search for articles by this author
  • Author Footnotes
    * This work was supported by funding from the Canada Bacterial Disease Network (Centers for Excellence Program) (to D. E. T.) and the Natural Sciences and Engineering Research Council (NSERC) (to M. M. P.).The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.The nucleotide sequence(s) reported in this paper has been submitted to the GenBank™/EMBL Data Bank with accession number(s) AF008596.
Open AccessPublished:August 22, 1997DOI:https://doi.org/10.1074/jbc.272.34.21357
      Helicobacter pylori is an important human pathogen which causes both gastric and duodenal ulcers and is also associated with gastric cancer and lymphoma. This microorganism has been shown to express cell surface glycoconjugates including Lewis X (Lex) and Lewis Y. These bacterial oligosaccharides are structurally similar to tumor-associated carbohydrate antigens found in mammals. In this study, we report the cloning of a novel α1,3-fucosyltransferase gene (HpfucT) involved in the biosynthesis of Lex within H. pylori. The deduced amino acid sequence of HpfucT consists of 478 residues with the calculated molecular mass of 56,194 daltons, which is approximately 100 amino acids longer than known mammalian α1,3/1,4-fucosyltransferases. The ∼52-kDa protein encoded byHpfucT was expressed in Escherichia coli CSRDE3 cells and gave rise to α1,3-fucosyltransferase activity but neither α1,4-fucosyltransferase nor α1,2-fucosyltransferase activity as characterized by radiochemical assays and capillary zone electrophoresis. Truncation of the C-terminal 100 amino acids of HpFuc-T abolished the enzyme activity. An approximately 72-amino acid region of HpFuc-T exhibits significant sequence identity (40–45%) with the highly conserved C-terminal catalytic domain among known mammalian and chicken α1,3-fucosyltransferases. These lines of evidence indicate that the HpFuc-T represents the bacterial α1,3-fucosyltransferase. In addition, several structural features unique to HpFuc-T, including 10 direct repeats of seven amino acids and the lack of the transmembrane segment typical for known eukaryotic α1,3-fucosyltransferases, were revealed. Notably, the repeat region contains a leucine zipper motif previously demonstrated to be responsible for dimerization of various basic region-leucine zipper proteins, suggesting that the HpFuc-T protein could form dimers.
      Helicobacter pylori is a spiral, microaerophilic Gram-negative bacterium which has been recognized as an important human pathogen causing gastritis and both peptic and duodenal ulcers (
      • Warren J.R.
      • Marshall B.J.
      ,
      • Graham G.Y.
      ,
      • Peterson W.I.
      ). This bacterium is also associated with an increased risk for the development of both gastric adenocarcinoma (
      • Parsonnet J.
      • Friedman G.D.
      • Vandersteen D.P.
      • Chang Y.
      • Vogelman J.H.
      • Orentreich N.
      • Sibley R.K.
      ,
      • Forman D.
      • Webb P.
      • Newell D.G.
      • Coleman M.
      • Palli D.
      • M⊘ller H.
      • Hengels K.
      • Elder J.
      • DeBacker G.
      ) and primary gastric lymphoma (
      • Nakamura S.
      • Yao T.
      • Lida M.
      • Fujishima M.
      • Tsuneyoshi M.
      ). This pathogen is highly adapted to colonize human gastric mucosa and may remain in the stomach with or without causing symptoms for many years (
      • Lee A.
      • Hazel S.L.
      ). Although H. pylori elicits local as well as systemic antibody responses (
      • Rathbone B.J.
      • Wyatt I.J.
      • Worsley B.W.
      • Shires S.E.
      • Trejdosiewicz L.K.
      • Heatley R.V.
      • Losowsky M.S.
      ), location in such a specific niche can permit it to escape elimination by the host immune response. Another mechanism by which H. pylori may protect itself from the action of the host immune response is the production of surface antigens mimicking those in the host.
      Cell surface α(1,3)- and α(1,2)-fucosylated oligosaccharides, that is, Lewis X (Lex)
      The abbreviations used are: Lex, Lewis X; Ley, Lewis Y; Fuc-T, α1,3-fucosyltransferase unless specified; kb, kilobase(s); PCR, polymerase chain reaction; ORF, open reading frame; HD-Zip, homeodomain-leucine zipper; bZip, basic region-zipper; TMR, tetramethylrhodamine; LacNAc-R, Galβ1–4GlcNAcβ-O-(CH2)8COOMe; Galβ1–3GlcNAc-R, Galβ1–3GlcNAcβ-O-(CH2)8COOMe; LacNAc-TMR, Galβ1–4GlcNAcβ-O-(CH2)8CO-NHCH2CH2NH-TMR; Phenyl-Gal, phenyl-β-galactoside.
      1The abbreviations used are: Lex, Lewis X; Ley, Lewis Y; Fuc-T, α1,3-fucosyltransferase unless specified; kb, kilobase(s); PCR, polymerase chain reaction; ORF, open reading frame; HD-Zip, homeodomain-leucine zipper; bZip, basic region-zipper; TMR, tetramethylrhodamine; LacNAc-R, Galβ1–4GlcNAcβ-O-(CH2)8COOMe; Galβ1–3GlcNAc-R, Galβ1–3GlcNAcβ-O-(CH2)8COOMe; LacNAc-TMR, Galβ1–4GlcNAcβ-O-(CH2)8CO-NHCH2CH2NH-TMR; Phenyl-Gal, phenyl-β-galactoside.
      and Lewis Y (Ley), are present on both eukaryotic and microbial cell surfaces. In mammals, Lex is a stage-specific embryonic antigen, and Lex, sLex, and Ley are all regarded as tumor-associated markers (
      • Feizi T.
      ,
      • Muramatsu T.
      ,
      • Hakomori S.
      ). sLexdirectly mediates cell to cell adhesion through the interaction with selectins (
      • Low J.B.
      ,
      • Springer T.A.
      ). It has been proposed that Lex plays a similar function during physiological and pathological processes (
      • Hakomori S.
      ). Bacterial Lex and Ley were first identified inH. pylori by Aspinall and Monteiro (
      • Aspinall G.O.
      • Monteiro M.A.
      ) and Aspinallet al. (
      • Aspinall G.O.
      • Monteiro M.A.
      • Pang H.
      • Walsh E.J.
      • Moran A.P.
      ) who demonstrated that Lex and Ley structures are present in the O-antigen regions of the lipopolysaccharides purified from H. pylori cells using one- and two-dimensional nuclear magnetic resonance spectroscopy. Expression of Lex in H. pylori was further confirmed by examination using immunoelectron microscopy and enzyme-linked immunosorbent assay (
      • Sherburne R.
      • Taylor D.E.
      ,
      • Chan N.W.C.
      • Stangier K.
      • Sherburne R.
      • Taylor D.E.
      • Zhang Y.
      • Dovichi N.
      • Palcic M.M.
      ,
      • Appelmelk B.J.
      • Simoons-Smit I.
      • Negrini R.
      • Moran A.P.
      • Aspinall G.O.
      • Forte J.G.
      • De Vries T.
      • Quan H.
      • Verboom T.
      • Maaskant J.J.
      • Ghiara P.
      • Kuipers E.J.
      • Bloemena E.
      • Tadema T.M.
      • Townsend R.R.
      • Tyagarajan K.
      • Crothers J.M.
      • Monteiro M.A.
      • Savio A.
      • De Graaff J.
      ). Recently it was reported that production of Lex and Ley is related to cagA+H. pylori isolates which are associated with an increased risk for the development of gastric cancer (
      • Wirth H.-P.
      • Yang M.
      • Karita M.
      • Blaser M.J.
      ). The biological functions of these bacterial oligosaccharide structures are not fully understood. It has been suggested that such glycoconjugates produced byH. pylori may mimic host cell antigens and could mask the bacterium and thus reduce the immune response (
      • Appelmelk B.J.
      • Simoons-Smit I.
      • Negrini R.
      • Moran A.P.
      • Aspinall G.O.
      • Forte J.G.
      • De Vries T.
      • Quan H.
      • Verboom T.
      • Maaskant J.J.
      • Ghiara P.
      • Kuipers E.J.
      • Bloemena E.
      • Tadema T.M.
      • Townsend R.R.
      • Tyagarajan K.
      • Crothers J.M.
      • Monteiro M.A.
      • Savio A.
      • De Graaff J.
      ,
      • Wirth H.-P.
      • Yang M.
      • Karita M.
      • Blaser M.J.
      ). It is also possible that these bacterial Lewis antigens could down-regulate the host T-cell response (
      • Sherburne R.
      • Taylor D.E.
      ). Therefore, production of such antigens may contribute to colonization and long-term infection of the stomach byH. pylori.
      The final step in the synthesis of cell surface α1,3- and α1,4-fucosylated oligosaccharides in mammals is catalyzed by α1,3- or α1,3/1,4-fucosyltransferases (Fuc-Ts). The human FUTgenes encoding at least five distinct Fuc-Ts generating Lexand related structures have been cloned and sequenced (
      • Goelz S.E.
      • Hession C.
      • Goff D.
      • Griffiths B.
      • Tizard R.
      • Newman B.
      • Chi-Rosso G.
      • Lobb R
      ,
      • Kukowska-Latallo J.F.
      • Larsen R.D.
      • Nair R.P.
      • Lowe J.B.
      ,
      • Lowe J.B.
      • Kukowska-Latallo J.F.
      • Nair R.P.
      • Larsen R.D.
      • Marks R.M.
      • Macher B.A.
      • Kelly R.
      • Ernst L.K.
      ,
      • Kumar R.
      • Potvin B.
      • Muller W.A.
      • Stanley P.
      ,
      • Weston B.W.
      • Nair R.P.
      • Larsen R.D.
      • Lowe J.B.
      ,
      • Weston B.W.
      • Smith P.L.
      • Kelly R.J.
      • Lowe J.B.
      ,
      • Koszdin K.L.
      • Bowen B.R.
      ,
      • Sasaki K.
      • Kurata K.
      • Funayama K.
      • Nagata M.
      • Watanabe E.
      • Ohta S.
      • Hanai N.
      • Nishi T.
      ,
      • Natsuka S.
      • Gersten K.M.
      • Zenita K.
      • Kannagi R.
      • Lowe J.B.
      ). Similar FUTs were also identified in other animals, including bovine (
      • Hadwiger J.A.
      • Wilkie T.M.
      • Strathmann M.
      • Firtel R.A.
      ), mouse (
      • Gersten K.M.
      • Natsuka S.
      • Trinchera M.
      • Petryniak B.
      • Kelly R.J.
      • Hiraiwa N.
      • Jenkins N.A.
      • Gilbert D.J.
      • Copeland N.G.
      • Lowe J.B.
      ), and chicken (
      • Lee K.P.
      • Carlson L.M.
      • Woodcock J.B.
      • Ramachandra N.
      • Schultz T.L.
      • Davis T.A.
      • Lowe J.B.
      • Thompson C.B.
      • Larsen R.D.
      ). The primary sequences of these eukaryotic Fuc-Ts exhibit significant amino acid similarity (
      • Lee K.P.
      • Carlson L.M.
      • Woodcock J.B.
      • Ramachandra N.
      • Schultz T.L.
      • Davis T.A.
      • Lowe J.B.
      • Thompson C.B.
      • Larsen R.D.
      ,
      • Kleene R.
      • Berger E.G.
      ). It has been demonstrated that the discrete peptide fragments of human Fuc-Ts III, V, and VI contribute to discrimination of acceptor substrates (
      • Legaul D.J.
      • Kelly R.J.
      • Natsuka Y.
      • Lowe J.B.
      ,
      • Xu Z.
      • Vo L.
      • Macher B.A.
      ).
      Chan et al. (
      • Chan N.W.C.
      • Stangier K.
      • Sherburne R.
      • Taylor D.E.
      • Zhang Y.
      • Dovichi N.
      • Palcic M.M.
      ) demonstrated that the Lexproduced by H. pylori is synthesized by the addition of galactose from UDP-Gal to GlcNAc and then fucose from GDP-Fuc to Galβ1–4GlcNAc (LacNAc), catalyzed by β1,4-galactosyltransferase and Fuc-T, respectively. This pathway is identical to that found in humans. However, the genetic basis for the bacterial Fuc-T was unclear. Characterization of a gene encoding the α1,3-fucosyltransferase would not only lead to elucidation of the pathogenic role of the Lex determinant in the H. pylori infection but would also provide new insights into the structure-function relationship by comparison between eukaryotic and prokaryotic Fuc-Ts. We now report the cloning and heterologous expression of the novel bacterial Fuc-T gene, designated HpfucT, obtained fromH. pylori. The deduced amino acid sequence ofHpfucT is similar to the highly conserved catalytic domain among known mammalian and chicken Fuc-Ts. Several sequence features unique to this bacterial Fuc-T were also identified. In addition, the HpFuc-T protein produced in Escherichia coli was characterized biochemically.

      DISCUSSION

      In this study we have cloned and sequenced the H. pylori α1,3-fucosyltransferase gene HpfucT. There are two unique features found in the DNA sequence of HpfucT as well as its flanking regions. First, in addition to a prokaryotic ribosomal binding site, the Kozak's consensus context (ribosomal binding site) also exists around the translation codon AUG. It will be of interest to determine whether or not this Kozak's context is functional in eukaryotic cells. Second, 10 direct 21-nucleotide repeats are present in the region close to the 3′ end of the HpfucTgene, which encode 10 corresponding 7 amino acid repeats in the HpFuc-T protein. Sequence analysis and expression of HpfucT inE. coli indicated that this gene coded for a protein of ∼56 kDa comprising 478 amino acids. Fucosyltransferase activity of HpFuc-T produced in E. coli cells was assayed by in vitro biochemical characterization, which demonstrated that this enzyme strictly utilizes LacNAc as an acceptor. No fucose transfer was detected when either Galβ1–3GlcNAc-R or Phenyl-Gal was used as an acceptor. Although the activity and the substrate specificity of HpFuc-T determined in vitro may or may not represent thein vivo situation of this enzyme, the lines of evidences presented here confirmed that the HpFuc-T represents the novel bacterial α1,3-fucosyltransferase.
      Amino acid sequence comparison revealed that HpFuc-T exhibits a significant sequence similarity to the highly conserved eukaryotic Fuc-T C-terminal catalytic domain. Beyond this region, the sequences between this bacterial Fuc-T and the eukaryotic Fuc-Ts extensively diverge. This is not surprising since the N-terminal amino acid sequences among these eukaryotic Fuc-Ts are relatively variable (
      • Kleene R.
      • Berger E.G.
      ). However, several unique structural features indicate that the HpFuc-T is distinct from eukaryotic Fuc-Ts. First, in comparison with the primary sequences of mammalian and chicken Fuc-Ts, the HpFuc-T protein contains an additional C-terminal ∼100amino acid region including the 10 direct repeats. Our preliminary characterization indicated that this region is crucial for Fuc-T activity since the deletion of this portion from the HpFuc-T protein completely abolishes the Fuc-T activity (Table I). This result is consistent with the previous finding that removal of one or more amino acids from the C terminus of Fuc-TV dramatically reduced or completely abolished enzyme activity (
      • Xu Z.
      • Vo L.
      • Macher B.A.
      ). Second, HpFuc-T does not contain a N-terminal transmembrane segment, a typical feature for mammalian Fuc-Ts, primarily consisting of hydrophilic residues (Fig. 2 B). It should be noted that the majority of the HpFuc-T activity is present in the membrane fraction, whereas Triton X-100 solubilization of the membrane fraction did not significantly increase such activity. This suggests that HpFuc-T could be associated with the cytoplasmic membrane through electrostatic forces as was found for the E. coli phosphatidylserine synthase whose overall amino acid sequence is also hydrophilic (
      • Louie K.
      • Chen Y.-C.
      • Dowhan W.
      ). Third, five potential asparagine-linked glycosylation sites lie within the HpFuc-T sequence, three of which are located in the C-terminal region downstream of the Fuc-T catalytic domain. These three C-terminal glycosylation sites are not found in mammalian and chicken α1,3-Fuc-Ts. An unexpected finding was that sites III and IV are comparable to those in α1,2-Fuc-Ts from humans and rabbit (
      • Paulson S.
      • Colley K.J.
      ).
      It is interesting that the sequence of the region containing the 10 direct repeats is extensively similar to the leucine-zipper domain of the plant HD-Zip proteins (ATHB-1 and -5 to -7) found in A. thaliana (
      • Ruberti I.
      • Sessa G.
      • Lucchetti S.
      • Morelli G.
      ,
      • Schena M.
      • Davis R.W.
      ,
      • Söderman E.
      • Mattsson J.
      • Sevenson M.
      • Borkird C.
      • Engström P.
      ). These highly conserved leucine residues also correspond to those in the leucine motif of the eukaryotic bZip proteins (Fig. 3 B). The leucine-zipper motif of plant HD-Zip proteins is closely linked to the homeodomain which consists of 61 amino acids with DNA-binding properties (
      • Kissinger C.R.
      • Beishan L.
      • Martin-Blanco E.
      • Kornberg T.B.
      • Pabo C.O.
      ,
      • Otting G.
      • Quian Y.Q.
      • Billeter M.
      • Müller M.
      • Affolter M.
      • Gehring W.G.
      • Wütrich K.
      ), whereas this motif in the bZip proteins is located immediately downstream of a basic region responsible for the sequence-specific DNA binding (
      • Oeda K.
      • Slinas J.
      • Chua N.-H.
      ,
      • Weisshaar B.
      • Armstrong G.A.
      • Block A.
      • da Costa a Silva O.
      • Hahlbrock K.
      ). In contrast, the putative leucine zipper domain in HpFuc-T follows the two potential glycosylation sites. Leucine zippers are responsible for dimerization in a separate class of transcription factors found in some eukaryotes (reviewed in Ref.
      • Bush S.J.
      • Sassone-Cosi P.
      ). More recently, a bZip motif was identified in a bacterial histidine kinase TodS regulating toluene degradation in Pseudomonas putida F1 (
      • Lau P.C.K.
      • Wang Y.
      • Patel A.
      • Labbé D.
      • Bergeron H.
      • Brousseau R.
      • Konishi Y.
      • Rawlings M.
      ). The bZip motif-mediated dimerization of TodS for DNA binding was suggested byin vitro DNA binding assays using a short dimerized peptide derived from the N-terminal region of TodS to mimic the full-length protein; this short peptide dimer could bind to the 196-base pair DNA fragment PCR-amplified from the intergenic region betweentodH and todS (
      • Lau P.C.K.
      • Wang Y.
      • Patel A.
      • Labbé D.
      • Bergeron H.
      • Brousseau R.
      • Konishi Y.
      • Rawlings M.
      ). In addition, the leucine zipper repeats of HpFuc-T exhibit significant sequence similarity (31% identity) to the multiple leucine zipper motifs of EAP-300, a developmentally regulated embryonal protein found in chicken (
      • Kelly M.M.
      • Phanhthourath C.
      • Brees D.K.
      • McCabe C.F.
      • Cole G.J.
      ). This protein has been implicated in a role of neural development, and it was postulated that existence of the multiple leucine-zipper motifs might enable EAP-300 to form dimers or multimers (
      • Kelly M.M.
      • Phanhthourath C.
      • Brees D.K.
      • McCabe C.F.
      • Cole G.J.
      ). We hypothesize that this leucine-zipper domain may dimerize the HpFuc-T protein. Such a dimer could act as either a transcription regulator controlling Lex production or a functional enzyme complex or both. Construction of mutations in this region would test this hypothesis. Additional studies on relationships between these structures and the α1,3-fucosyltransferase functions, and transcriptional and translational regulation of this gene, should shed light on the pathogenic role of this gene product during H. pyloriinfection.

      Acknowledgments

      We thank Margaret Deschiffart for technical assistance.

      REFERENCES

        • Warren J.R.
        • Marshall B.J.
        Lancet. 1983; i: 1273-1275
        • Graham G.Y.
        J. Gastroenterol. Hepatol. 1991; 6: 105-113
        • Peterson W.I.
        N. Engl. J. Med. 1991; 324: 1043-1048
        • Parsonnet J.
        • Friedman G.D.
        • Vandersteen D.P.
        • Chang Y.
        • Vogelman J.H.
        • Orentreich N.
        • Sibley R.K.
        N. Engl. J. Med. 1991; 325: 1127-1131
        • Forman D.
        • Webb P.
        • Newell D.G.
        • Coleman M.
        • Palli D.
        • M⊘ller H.
        • Hengels K.
        • Elder J.
        • DeBacker G.
        Lancet. 1993; 341: 1359-1362
        • Nakamura S.
        • Yao T.
        • Lida M.
        • Fujishima M.
        • Tsuneyoshi M.
        Cancer. 1997; 79: 3-11
        • Lee A.
        • Hazel S.L.
        Microb. Ecol. Health Dis. 1988; 1: 1-16
        • Rathbone B.J.
        • Wyatt I.J.
        • Worsley B.W.
        • Shires S.E.
        • Trejdosiewicz L.K.
        • Heatley R.V.
        • Losowsky M.S.
        Gut. 1986; 27: 642-647
        • Feizi T.
        Nature. 1985; 314: 53-57
        • Muramatsu T.
        Biochemie. 1988; 70: 1587-1596
        • Hakomori S.
        Adv. Cancer Res. 1989; 52: 257-331
        • Low J.B.
        Fukuda M. Hindsgaul O. Frontiers in Molecular Biology. Oxford University Press, Oxford1994: 163-205
        • Springer T.A.
        Annu. Rev. Physiol. 1995; 57: 827-872
        • Hakomori S.
        Histochem. J. 1992; 24: 771-776
        • Aspinall G.O.
        • Monteiro M.A.
        Biochemistry. 1996; 35: 2498-2504
        • Aspinall G.O.
        • Monteiro M.A.
        • Pang H.
        • Walsh E.J.
        • Moran A.P.
        Biochemistry. 1996; 35: 2489-2497
        • Sherburne R.
        • Taylor D.E.
        Infect. Immun. 1995; 63: 4564-4568
        • Chan N.W.C.
        • Stangier K.
        • Sherburne R.
        • Taylor D.E.
        • Zhang Y.
        • Dovichi N.
        • Palcic M.M.
        Glycobiology. 1995; 5: 683-688
        • Appelmelk B.J.
        • Simoons-Smit I.
        • Negrini R.
        • Moran A.P.
        • Aspinall G.O.
        • Forte J.G.
        • De Vries T.
        • Quan H.
        • Verboom T.
        • Maaskant J.J.
        • Ghiara P.
        • Kuipers E.J.
        • Bloemena E.
        • Tadema T.M.
        • Townsend R.R.
        • Tyagarajan K.
        • Crothers J.M.
        • Monteiro M.A.
        • Savio A.
        • De Graaff J.
        Infect. Immun. 1996; 64: 2031-2040
        • Wirth H.-P.
        • Yang M.
        • Karita M.
        • Blaser M.J.
        Infect. Immun. 1996; 64: 4598-4605
        • Goelz S.E.
        • Hession C.
        • Goff D.
        • Griffiths B.
        • Tizard R.
        • Newman B.
        • Chi-Rosso G.
        • Lobb R
        Cell. 1990; 63: 1349-1356
        • Kukowska-Latallo J.F.
        • Larsen R.D.
        • Nair R.P.
        • Lowe J.B.
        Genes Dev. 1990; 4: 1288-1303
        • Lowe J.B.
        • Kukowska-Latallo J.F.
        • Nair R.P.
        • Larsen R.D.
        • Marks R.M.
        • Macher B.A.
        • Kelly R.
        • Ernst L.K.
        J. Biol. Chem. 1991; 266: 17467-17477
        • Kumar R.
        • Potvin B.
        • Muller W.A.
        • Stanley P.
        J. Biol. Chem. 1991; 266: 21777-21783
        • Weston B.W.
        • Nair R.P.
        • Larsen R.D.
        • Lowe J.B.
        J. Biol. Chem. 1992; 267: 4152-4160
        • Weston B.W.
        • Smith P.L.
        • Kelly R.J.
        • Lowe J.B.
        J. Biol. Chem. 1992; 267: 24575-24584
        • Koszdin K.L.
        • Bowen B.R.
        Biochem. Biophys. Res. Commun. 1992; 187: 152-157
        • Sasaki K.
        • Kurata K.
        • Funayama K.
        • Nagata M.
        • Watanabe E.
        • Ohta S.
        • Hanai N.
        • Nishi T.
        J. Biol. Chem. 1994; 269: 14730-14737
        • Natsuka S.
        • Gersten K.M.
        • Zenita K.
        • Kannagi R.
        • Lowe J.B.
        J. Biol. Chem. 1994; 269: 16789-16794
        • Hadwiger J.A.
        • Wilkie T.M.
        • Strathmann M.
        • Firtel R.A.
        Proc. Natl. Acad. Sci. U. S. A. 1991; 88: 8213-8217
        • Gersten K.M.
        • Natsuka S.
        • Trinchera M.
        • Petryniak B.
        • Kelly R.J.
        • Hiraiwa N.
        • Jenkins N.A.
        • Gilbert D.J.
        • Copeland N.G.
        • Lowe J.B.
        J. Biol. Chem. 1995; 270: 25047-25056
        • Lee K.P.
        • Carlson L.M.
        • Woodcock J.B.
        • Ramachandra N.
        • Schultz T.L.
        • Davis T.A.
        • Lowe J.B.
        • Thompson C.B.
        • Larsen R.D.
        J. Biol. Chem. 1996; 271: 32960-32967
        • Kleene R.
        • Berger E.G.
        Biochim. Biophys. Acta. 1993; 1154: 283-325
        • Legaul D.J.
        • Kelly R.J.
        • Natsuka Y.
        • Lowe J.B.
        J. Biol. Chem. 1995; 270: 20987-20996
        • Xu Z.
        • Vo L.
        • Macher B.A.
        J. Biol. Chem. 1996; 271: 8818-8823
        • Ge Z.
        • Taylor D.E.
        J. Bacteriol. 1996; 178: 6151-6157
        • Sambrook J.
        • Fritsch E.F.
        • Maniatis T.
        Molecular Cloning: A Laboratory Manual.
        2nd Ed. Cold Spring Harbor Laboratory Press, Cold Spring Harbor, NY1989
        • Gokhale U.B.
        • Hindsgaul O.
        • Palcic M.M.
        Can. J. Chem. 1990; 68: 1063-1071
        • Shine J.
        • Dalgarno L.
        Proc. Natl. Acad. Sci. U. S. A. 1974; 71: 1342-1346
        • Kozak M.
        Cell. 1986; 44: 283-292
        • Platt T.
        Annu. Rev. Biochem. 1986; 55: 339-372
        • Kyte J.
        • Doolittle R.F.J.
        J. Mol. Biol. 1982; 157: 105-132
        • Paulson S.
        • Colley K.J.
        J. Biol. Chem. 1996; 264: 17615-17618
        • Hitoshi S.
        • Kusunoki S.
        • Kanazawa I.
        • Tsuji S.
        J. Biol. Chem. 1989; 271: 16975-16981
        • Joziasse D.H.
        Glycobiology. 1992; 2: 271-277
        • Ruberti I.
        • Sessa G.
        • Lucchetti S.
        • Morelli G.
        EMBO J. 1991; 10: 1787-1791
        • Schena M.
        • Davis R.W.
        Proc. Natl. Acad. Sci. U. S. A. 1992; 89: 3894-3898
        • Söderman E.
        • Mattsson J.
        • Sevenson M.
        • Borkird C.
        • Engström P.
        Plant Mol. Biol. 1994; 26: 145-154
        • Oeda K.
        • Slinas J.
        • Chua N.-H.
        EMBO J. 1991; 10: 1793-1802
        • Weisshaar B.
        • Armstrong G.A.
        • Block A.
        • da Costa a Silva O.
        • Hahlbrock K.
        EMBO J. 1991; 10: 1777-1786
        • Kelly M.M.
        • Phanhthourath C.
        • Brees D.K.
        • McCabe C.F.
        • Cole G.J.
        Dev. Brain Res. 1995; 85: 31-47
        • Lau P.C.K.
        • Wang Y.
        • Patel A.
        • Labbé D.
        • Bergeron H.
        • Brousseau R.
        • Konishi Y.
        • Rawlings M.
        Proc. Natl. Acad. Sci. U. S. A. 1997; 94: 1453-1458
        • Louie K.
        • Chen Y.-C.
        • Dowhan W.
        J. Bacteriol. 1986; 165: 802-812
        • Kissinger C.R.
        • Beishan L.
        • Martin-Blanco E.
        • Kornberg T.B.
        • Pabo C.O.
        Cell. 1990; 63: 579-590
        • Otting G.
        • Quian Y.Q.
        • Billeter M.
        • Müller M.
        • Affolter M.
        • Gehring W.G.
        • Wütrich K.
        EMBO J. 1990; 9: 3085-3092
        • Bush S.J.
        • Sassone-Cosi P.
        Trends Genet. 1990; 6: 36-40