Characterization of centrin genes in Paramecium

Centrins are highly conserved, ubiquitous cytoskeletal components which belong to the EF-hand superfamily of Ca2+-modulated proteins. We report here the molecular characterization of new members of the centrin family, Paramecium centrins. Previous studies described the organization of the infraciliary lattice (ICL), the innermost cortical cytoskeletal network of Paramecium, and showed that it was composed of a set of low-molecular-mass, Ca2+-binding polypeptides [Garreau de Loubresse, N., Klotz, C., Vigues, B., Rutin, J & Beisson, J. (1991) Biol. Cell 71, 217-225]. In this paper we show that these polypeptides are recognized by specific anti-centrin polyclonal antibodies. Their microsequences revealed four distinct N-termini. For one of them, ICL1, N-terminal and internal peptide sequences were used for PCR amplification and cloning of a DNA fragment containing a complete centrin coding sequence. The deduced amino acid sequence presents about 50% identify with those of centrins from other species. Further molecular analysis allowed us to identify two additional closely related, co-expressed ICL1 genes, providing the first example of a centrin multigenic family in a microorganism.

Characterization of a novel elastase inhibitor from a fan coral

An acidic hydromethanolic extract of the tropical gorgonian Melithea cf. stormii exhibited anti-elastase activity. From the polypeptidic mixture we isolated and purified to homogeneity a protein with a molecular mass determined at 21,159 Da by Maldi/Tof mass spectrometric analysis. The novel protein of marine invertebrate origin strongly inhibited amidolysis of Suc(Ala) 3pNA by porcine pancreatic elastase (PPE) and was labelled iela melst. The N-terminal aminoacid sequence of its 39-first residues revealed the characteristics of a non-classical Kazal-type domain. Iela melst behaved as a reversible tight-binding inhibitor of PPE. The competitive inhibition followed Cha's mechanism A with an equilibrium dissociation constant, Ki, calculated as 1.5 x 10(-9) M.

Posttranslational modifications in the C-terminal tail of axonemal tubulin from sea urchin sperm

After proteolytic digestion of sperm tubulin from sea urchin Paracentrotus lividus, C-terminal peptides were isolated by chromatographic separations. The peptides were analyzed by Edman degradation and matrix-assisted laser desorption/ionization-time of flight mass spectrometry. About 70% of the isolated C-terminal peptides were unmodified. The remaining modified peptides have undergone a combination of numerous posttranslational modifications generating significant heterogeneity of sperm tubulin. alpha-Tubulin is modified by detyrosylation, release of the penultimate glutamate, polyglutamylation, and polyglycylation. Glycylation and glutamylation can coexist within one alpha-tubulin isoform. beta-Tubulin undergoes polyglycylation but was not observed to be polyglutamylated. The number of units posttranslationally added reaches 11 and 12 glycyl units on beta- and alpha-tubulin, respectively. This is different from the polyglycylation of axonemal tubulin in Paramecium cilia where up to 40 added glycyl units were observed both on alpha- and beta-tubulin.

Purification, in vitro reassembly, and preliminary sequence analysis of epiplasmins, the major constituent of the membrane skeleton of Paramecium

The epiplasmic layer, a continuous rigid granulo-fibrillar sheet directly subtending the surface membranes of Paramecium, is one of the outermost of the various cytoskeletal networks that compose it cortex. We have previously shown that the epiplasm consists of a set of 30 to 50 protein bands on SDS-PAGE in the range 50 to 33 kDa, the epiplasmins. We report a purification procedure for the set of epiplasmic proteins, a description of their physicochemical and reassembly properties, and a preliminary characterization of their sequence. The conditions for solubilization of the epiplasm and for in vitro reassembly of its purified constituents ar described. Reassembly of the entire set of proteins and of some (but not all) subsets are shown to yield filamentous aggregates. Microsequences of two purified bands of epiplasmins reveal a striking amino acid sequence consisting of heptad repeats of only three main amino acids, P, V, and Q. These repeats were confirmed by DNA sequencing of polymerase chain reaction products. The motif is QPVQ-h, in which h is a hydrophobic residue. This may constitute the core of the epiplasmin sequence and, in view of the tendency of such a sequence to form a coiled-coil, may account for the remarkable self-aggregation properties of epiplasmins.

The relationships between the toxicity and the primary and secondary structures of elicitinlike protein elicitors secreted by the phytopathogenic fungus Pythium vexans

Elicitins are toxic and signaling proteins secreted by Phytophthora spp. responsible for the incompatible reaction and systemic hypersensitive-like necroses of diverse plant species leading to resistance against fungal or bacterial plant pathogens. Such proteins were observed in the culture filtrate of another species of the Oomycete genus, Pythium vexans. Two alpha elicitinlike proteins were purified and sequenced. One of these novel elicitins (Vex2) exhibited a 100-residue sequence instead of 98 while the other (Vex1) had an N-glycosylation site, effectively glycosylated (equivalent of 16 hexose residues). In addition to the point mutations already observed in Phytophthora species, we found several novel amino acid changes. Furthermore, circular dichroism revealed some differences in their structure in solution compared with the Phytophthora elicitins that were correlated with specific point mutations. These sequences permitted the establishment of a phylogenic tree, suggesting that Pythium vexans is a species close to the Phytophthora genus. The toxicity of the Pythium vexans elictins to tobacco leaves was investigated and correlated with the occurrence of the carbohydrate moiety of one of the two isoforms, observed for the first time in an elicitin.

ERGIC-53, a membrane protein of the endoplasmic reticulum-Golgi intermediate compartment, is identical to MR60, an intracellular mannose-specific lectin of myelomonocytic cells

A mannose-specific membrane lectin (MR60) isolated from human myelomonocytic HL60 cells by affinity chromatography is expressed in intracellular organelles of immature monocytes (Pimpaneau, V., Midoux, P., Monsigny, M., and Roche, A. C. (1991) Carbohydr. Res. 213, 95-108). It is not present at the cell surface and is immunochemically and structurally distinct from the M(r) 175,000 mannose receptor of mature macrophages. MR60 cDNA was isolated and characterized; on the basis of its sequence, MR60 is not related to any known mammalian lectins. Surprisingly, MR60 was found to be identical to ERGIC-53 (Schindler, R., Itin, C., Zerial, M., Lottspeich, F., and Hauri, H.P. (1993) Eur. J. Cell Biol. 61, 1-9), a type I integral membrane protein, defined as a marker of the intermediate compartment that recycles between the Golgi apparatus and endoplasmic reticulum; MR60/ERGIC-53 shares with VIP-36 significant homologies with leguminous plant lectins (Fiedler, K., and Simmons, K. (1994) Cell 77, 625-626). We extend these findings in evidencing a structural homology between MR60/ERGIC-53 and mammalian galectins (soluble beta galactose binding proteins). MR60/ERGIC-53 is the first lectin characterized as an endoplasmic reticulum-Golgi protein. Accordingly, this intracellular mannose binding protein could be involved in the traffic of glycoproteins between endoplasmic reticulum and the Golgi apparatus.

Electrospray mass spectrometry for the characterization of the purity of natural and modified oligodeoxynucleotides

Electrospray ionization mass spectrometry is an accurate and sensitive analytical method to characterize the purity of oligodeoxynucleotides being tested for pharmacological studies. We report the preparation procedure ('desalting') of natural and modified oligodeoxynucleotides (ODNs) and their analysis by negative-ion electrospray mass spectrometry. We evaluate the sensitivity and the accuracy of the method for two antisense ODN sequences. Mass analysis of the 25-mer phosphorothioate can be performed to within 0.001% accuracy (standard error of 0.05 Da) for a sample concentration of 12 pmol/microL. In addition, the adduct ion and the failure sequence can be identified to characterize the antisense ODN.

Purification of arginase from Aspergillus nidulans

Arginase (EC 3.5.3.1) of Aspergillus nidulans, the enzyme which enables the fungus to use arginine as the sole nitrogen source was purified to homogeneity. Molecular mass of the purified arginase subunit is 40 kDa and is similar to that reported for the Neurospora crassa (38.3 kDa) and Saccharomyces cerevisiae (39 kDa) enzymes. The native molecular mass of arginase is 125 kDa. The subunit/native molecular mass ratio suggests a trimeric form of the protein. The arginase protein was cleaved and partially sequenced. Two out of the six polypeptides sequenced show a high degree of homology to conserved domains in arginases from other species.

Polyglycylation of tubulin: a posttranslational modification in axonemal microtubules

A posttranslational modification was detected in the carboxyl-terminal region of axonemal tubulin from Paramecium. Tubulin carboxyl-terminal peptides were isolated and analyzed by Edman degradation sequencing, mass spectrometry, and amino acid analysis. All of the peptides, derived from both alpha and beta tubulin subunits, were modified by polyglycylation, containing up to 34 glycyl units covalently bound to the gamma carboxyl group of glutamyl residues. This modification, present in one of the most stable microtubular systems, may influence microtubule stability or axoneme function, or both.

Class I and IVa beta-tubulin isotypes expressed in adult mouse brain are glutamylated

Several types of post-translational modifications contribute to the high level of tubulin heterogeneity in the brain. An important modification is glutamylation of the major brain-specific isotypes, such as class Ia/b of alpha-tubulin and classes II and III of beta-tubulin. Here we describe experiments to determine if additional, minor tubulin isotypes, expressed in adult mouse brain, could also be glutamylated. Purified tubulin from adult mouse brain was cleaved with thermolysin. Proteolytically released carboxy-terminal peptides of both alpha- and beta-tubulin were isolated by sequential anion exchange and reverse-phase column-chromatography. Anionic peptides were then characterized by amino acid sequencing and mass spectrometry. We show that brain-specific class IVa and constitutive class I beta-tubulin isotypes can be glutamylated, at Glu434 and Glu441, respectively.

Evidence for a conformational polymorphism of invertebrate neurohormones. D-amino acid residue in crustacean hyperglycemic peptides

Several large peptidic neurohormones have been isolated in crustaceans. In lobster and other related species, each of these neurohormones, and particularly the crustacean hyperglycemic hormone, occurs as two isoforms having the same peptidic sequence and molecular mass. We report here that these isoforms differ by the configuration of a single amino acid residue. The third residue (Phe3) of the lobster hyperglycemic hormones is in either the L- or D-configuration. In addition, we have shown that the biological activity of the two isoforms differs when considering the kinetics of their hyperglycemic effect.

Purification and biological activity of a recombinant human erythropoietin produced by lymphoblastoid cells

A recombinant human erythropoietin (rH-EPO) was obtained from the culture supernatants of human B-lymphoblastoid cells transfected by the human EPO gene. rH-EPO was purified by a two-step method based on immunoaffinity and ion exchange chromatography. The first step was achieved by an anti-EPO monoclonal antibody (Mab). This Mab, immobilized on Sepharose 4B, allowed a 410-fold purification of the protein. The second step consisted of ion exchange chromatography on DEAE Sephacel. The combination of these two steps results in a highly purified rH-EPO with a global yield of about 50%; the specific activity of the protein was 176,000 IU/A280. The NMR spectrum was characteristic for a well structured, single-conformation protein. The purified protein was analyzed by SDS-PAGE and isoelectric focusing. The biological activity of purified rH-EPO was measured in vivo, by the incorporation of 59Fe into red blood cells (RBC) of polycythemic mice and in vitro by the proliferative response of an EPO-dependent cell line. The purified protein expressed in lymphoblastoid cells of human origin had the same biological activity as that of urinary EPO and rH-EPO produced in other mammalian cells.

Protein processing and morphogenesis of secretory granules in Paramecium

The ciliated protozoan Paramecium provides a model system for the study of regulated secretion, featuring architecturally complex secretory storage granules-trichocysts-docked at the plasma membrane, ready to respond to an exocytotic stimulus. The trichocysts are characterized by crystalline contents that confer upon the organelle a defined shape which can be altered by single gene mutation. The crystalline trichocyst contents are built up from a heterogeneous set of small acidic polypeptides generated by proteolytic maturation of a family of precursor molecules, suggesting an important role for protein processing in this system. We have recently shown that the primary defect in several secretory mutants lacking functional trichocysts is in intracellular trafficking rather than protein processing. However, analysis of how these defects lead to altered trichocyst shape supports the notion that the protein processing is essential for morphogenesis. Preliminary results of a cloning project reveal that an extensive multigene family (approximately 100 genes) codes for the trichocyst matrix proteins. Deduced amino acid sequences of putative processing sites indicate that (at least) two distinct processing reactions are probably involved in the maturation of these proteins, and allow us to speculate that each reaction may control a key event of trichocyst biogenesis.

Four 9-kDa proteins excreted by somatic embryos of grapevine are isoforms of lipid-transfer proteins

Four 9-kDa small extracellular proteins produced by embryogenic cultures in the absence of auxin have been purified from the extracellular medium of grapevine somatic embryo cultures through cation-exchange chromatography and hydrophobic-interaction chromatography. The partial amino-acid sequences reflect high similarities between the four proteins as well as with the sequences established for carrot, spinach, millet and maize nonspecific lipid-transfer proteins. All these sequences show conservation of three cysteines at positions 4, 14 and 30-32, as well as glycine, valine, tyrosine and lysine residues at positions 5, 7, 17 and 37, respectively. In-vitro lipid-transfer assays reveal that the four proteins catalyze the transfer of phosphatidylcholine from liposomes towards mitochondria with an efficiency similar or higher than that of a purified maize lipid-transfer protein.

Electrospray ionization mass spectrometry on hydrophobic peptides electroeluted from sodium dodecyl sulfate-polyacrylamide gel electrophoresis application to the topology of the sarcoplasmic reticulum Ca2+ ATPase

We describe a method to prepare proteins and peptides in a state suitable for exact determination of molecular mass by electrospray ionization mass spectrometry after sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and electroelution. The utility of the procedure, in conjunction with N-terminal sequencing, in defining the C-terminal end of the peptide fragments produced by proteolysis of sarcoplasmic reticulum Ca2+ ATPase with V8 is demonstrated. The application of mass spectrometry aids significantly the use of proteolytic enzymes for topological studies of membrane proteins, and SDS-PAGE is preferable to reverse-phase HPLC for separation of membraneous, hydrophobic peptides and proteins.

Frog prodermorphin expressed in mammalian cells is partly converted to the hydroxyproline containing precursor

Using recombinant vaccinia virus, we have expressed in mammalian cells the cDNA coding for the precursor of dermorphin, a D-alanine containing opioid peptide from the skin of the South American frog Phyllomedusa sauvagei. HeLa cells and AtT-20 cells produced prodermorphin where proline-6 of dermorphin was partly hydroxylated. This was demonstrated by digesting the partially purified precursors with trypsin and carboxypeptidase B. After immunoprecipitation and separation by HPLC, two decapeptides were detected which differed by the presence of proline or hydroxy-proline at position 6. This demonstrates that HeLa cells as well as AtT-20 cells can perform the post-translational conversion of certain proline residues to hydroxyproline in a foreign hormone precursor expressed in these cells.

Photo-cross-linking of CRP to nonspecific DNA in the absence of cAMP. DNA interacts with both the N- and C-terminal parts of the protein

Adenosine cyclic 3',5'-phosphate receptor protein (CRP or CAP) is a regulatory protein involved in the transcription of several operons in Escherichia coli. cAMP-independent, nonspecific complexes of CRP and DNA were investigated by photochemical cross-linking of the protein to nonspecific DNA, whose thymines are substituted by 5-bromouracil (BrUra). The cross-linked protein was completely digested by trypsin, and the covalently bound peptides were sequenced. We identified two regions of the protein in close contact with DNA: one in the C-terminal part, overlapping the canonical helix-turn-helix motif, and the other one in the N-terminal part, which is usually not considered to belong to the DNA-interacting domain of CRP. This result lead us to propose models for nonspecific interaction, where the DNA is in contact with both the N- and C-terminal parts of the protein.

The asiA gene of bacteriophage T4 codes for the anti-sigma 70 protein

The anti-sigma 70 factor of bacteriophage T4 is a 10-kDa (10K) protein which inhibits the sigma 70-directed initiation of transcription by Escherichia coli RNA polymerase holoenzyme. We have partially purified the anti-sigma 70 factor and obtained the sequence of a C-terminal peptide of this protein. Using reverse genetics, we have identified, at the end of the lysis gene t and downstream of an as yet unassigned phage T4 early promoter, an open reading frame encoding a 90-amino-acid protein with a predicted molecular weight of 10,590. This protein has been overproduced in a phage T7 expression system and partially purified. It shows a strong inhibitory activity towards sigma 70-directed transcription (by RNA polymerase holoenzyme), whereas it has no significant effect on sigma 70-independent transcription (by RNA polymerase core enzyme). At high ionic strength, this inhibition is fully antagonized by the neutral detergent Triton X-100. Our results corroborate the initial observations on the properties of the phage T4 10K anti-sigma 70 factor, and we therefore propose that the gene which we call asiA, identified in the present study, corresponds to the gene encoding this T4 transcriptional inhibitor.

BEN, a surface glycoprotein of the immunoglobulin superfamily, is expressed in a variety of developing systems

We have previously identified a 95- to 100-kDa cell surface glycoprotein, which we named BEN (for bursal epithelium and neurons), that is widely expressed during chicken embryonic development. In the central nervous system, it is restricted to subsets of neurons including the motoneurons and the inferior olivary nucleus neurons (which provide the cerebellum with the climbing fibers) where its expression occurs during the phase of axonogenesis and synaptogenesis. In the present work, we show that BEN expression extends to a variety of tissues originating from the three embryonic germ layers. We have found that BEN immunopurified from neural, epithelial, and hemopoietic tissues is differently glycosylated and may or may not carry the HNK-1 epitope. We then cloned a full-length cDNA encoding this protein. Analysis of its sequence reveals that BEN is a member of the immunoglobulin superfamily. Two molecules with an identical cDNA sequence were recently reported: DM-GRASP [Burns, F. R., Von Kannen, S., Guy, L., Raper, J. A., Kamholz, J. & Chang, S. (1991) Neuron 7, 209-220] and SC1 [Tanaka, H., Matsui, T., Agata, A., Tomura, M., Kubota, I., Mcfarland, K. C., Kohr, B., Lee, A., Phillips, H. S. & Shelton, D. L. (1991) Neuron 7, 535-545]. Their pattern of expression and structural properties are consistent with those reported for BEN. Therefore BEN, DM-GRASP, and SC1 are likely to be the same molecule of the immunoglobulin superfamily.

Structure of the polyglutamyl side chain posttranslationally added to alpha-tubulin

Polyglutamylation, a new posttranslational modification of tubulin identified originally on the acidic alpha variants by Eddé et al. (Eddé, B., Rossier, J., Le Caer, J. P., Desbruyeres, E., Gros, F., and Denoulet, P. (1990) Science 247, 83-85), consists of the successive addition of glutamyl units to the Glu445. To characterize their linkage mode mouse tubulin was posttranslationally labeled with [3H]glutamate. After digestion of [3H]tubulin with thermolysin, up to eight radioactive peaks were separated on an anion exchange column (DEAE). Combined use of Edman degradation sequencing and mass spectrometry analysis of the first 6 one indicated that they all correspond to the same COOH-terminal sequence 440VEGEGEEEGEE450 bearing one to six glutamyl units on the Glu445. The first glutamyl residue is amide-linked to the gamma-carboxyl group of Glu445, but the additional residues can be linked to the gamma- or alpha-carboxyl groups of the preceding one. All possible linkages for the biglutamylated tubulin peptides (gamma 1 alpha 2, gamma 1 gamma 2) and triglutamylated (gamma 1 alpha 2 alpha 3, gamma 1 alpha 2 gamma 3, gamma 1 alpha 2 gamma 2, gamma 1 gamma 2 alpha 3, gamma 1 gamma 2 gamma 3) were synthesized. These different peptides were successfully separated on a C18 5-micron reverse phase column. We found that the bi- and triglutamylated tubulin peptides behave as the gamma 1 alpha 2 and gamma 1 alpha 2 alpha 3 synthetic peptides, respectively. These results indicate that the second and third glutamyl residues of the polyglutamyl side chain are amide-linked to the alpha-carboxyl group of the preceding unit.

Characterization of a major brain tubulin variant which cannot be tyrosinated

Brain tubulin preparations contain an abundant type of tubulin which does not undergo the normal cycle of tyrosination-detyrosination, and whose nature is still unknown. We have used peptide sequence analysis and mass spectrometry combined with immunological procedures to show that this non-tyrosinatable tubulin has a specific primary structure. It differs from the tyrosinated isotype in that it lacks a carboxy-terminal glutamyl-tyrosine group on its alpha-subunit. Thus, non-tyrosinatable tubulin originates from a well-defined posttranslational modification of the tubulin primary structure which is located at the expected site of activity of tubulin tyrosine ligase. This probably accounts for the reason why it cannot be tyrosinated. The significance of this abundant brain isotubulin and the metabolic pathway involved in its formation remain to be elucidated. This should shed light on the relation between the structural diversity of the carboxy terminus of alpha-tubulin and the regulation of functional properties of microtubules.

Phosphorylation of human recombinant tyrosine hydroxylase isoforms 1 and 2: an additional phosphorylated residue in isoform 2, generated through alternative splicing

The single human tyrosine hydroxylase (TH) gene generates four different mRNA species through alternative splicing events. TH-1 and TH-2 mRNAs are expressed mostly in the brain. We have produced large amounts of the corresponding proteins in Escherichia coli to analyze their respective molecular characteristics. The polypeptides have molecular weights similar to those of TH expressed in Xenopus oocytes and react with antibodies to TH. The two isoforms were purified with a purity of 90% using a three-step procedure. The phosphorylation sites have been determined in the two isoforms after labeling with [gamma-32P]ATP in the presence of cAMP-dependent protein kinase (PKA) or calmodulin-dependent protein kinase II (CaM-PK II). In both isoforms, Ser-40 was found to be phosphorylated by PKA, and Ser-19 and Ser-40 were found to be phosphorylated by CaM-PK II. The putative phosphorylation site generated by alternative splicing (Ser-31) was phosphorylated specifically by CaM-PK II in TH-2 only. The kinetic properties of the two isoforms in the presence of various concentrations of the substrate (tyrosine) and of the natural cofactor [6R)-tetrahydrobiopterin) were also analyzed. TH produced in E. coli is unphosphorylated but nevertheless active. At 50 microM tyrosine and 300 microM (6R)-tetrahydrobiopterin, the specific activities of TH-1 and TH-2 are 1300 and 620 nmol of dihydroxyphenylalanine/min/mg, respectively. Phosphorylation of TH-1 and TH-2 by PKA activates both isoenzymes as shown by the increase in the affinity for the cofactor. No changes in kinetic parameters of the isoenzymes were observed after phosphorylation by CaM-PK II. Dopamine was found to inhibit both TH isoenzymes to the same extent as shown by their similar Ki values for dopamine. These values were increased after phosphorylation of each enzyme by PKA. Unlike TH-1, phosphorylation of TH-2 by CaM-PK II resulted in an increase of the Ki value for dopamine. This property may be related to the presence of the additional phosphorylated residue in TH-2 isoform.

Primary structure of two isoforms of the vitellogenesis inhibiting hormone from the lobster Homarus americanus

The amino acid sequence of two isoforms of the Vitellogenesis Inhibiting Hormone from the lobster Homarus americanus (one biologically active and one inactive in a heterologous bioassay) has been established by gas-phase microsequencing and fast-atom bombardment mass spectrometry. These two isoforms, isolated from sinus glands display the same sequence of 77 amino acid residues (m.w.: 9135 Da) and have a free N-terminus. Structurally related to Crustacean Hyperglycemic Hormone and Molt Inhibiting Hormone, the Vitellogenesis Inhibiting Hormone of the lobster clearly appears as an original member of the newly described family of neuropeptides, so far proper to crustaceans, which are involved in the control of major physiological functions.

A combination of posttranslational modifications is responsible for the production of neuronal alpha-tubulin heterogeneity

We describe the presence of alpha-tubulin and MAP2 acetyltransferase activities in mouse brain. The enzyme(s) copurified with microtubules through two cycles of assembly-disassembly. Incubation of microtubule proteins with [3H]acetyl CoA resulted in a strong labeling of both alpha-tubulin and MAP2. To determine the site of the modification, tubulin was purified and digested with Glu-C endoproteinase. A unique radioactive peptide was detected and purified by HPLC. Edman degradation sequencing showed that this peptide contained epsilon N-acetyllysine at position 40 of the alpha-tubulin molecule. This result demonstrates that mouse brain alpha-tubulin was acetylated at the same site as in Chlamydomonas. Isoelectric focusing analysis showed that acetylated alpha-tubulin was resolved into five isoelectric variants, denoted alpha 3 and alpha 5 to alpha 8. This heterogeneity is not due to acetylation of other sites but results from a single acetylation of Lys40 of an heterogeneous population of alpha-tubulin isoforms. These isoforms are produced by posttranslational addition of one to five glutamyl units. Thus, neuronal alpha-tubulin is extensively modified by a combination of modifications including acetylation, glutamylation, tyrosylation, and other yet unknown modifications.

Molecular cloning of RI-HB, a heparin binding protein regulated by retinoic acid

RI-HB is an extracellular heparin binding protein regulated by retinoic acid and essentially expressed during embryogenesis. This study reports the cloning and sequencing of the cDNA that encodes RI-HB. The sequence of RI-HB contains 121 amino acid residues and is very rich in basic amino acids and cysteines. This sequence was compared to those of HBGAM and MK protein, two other heparin binding proteins exhibiting growth and/or neurotrophic activities. Northern blot analysis indicates that RI-HB mRNA is strongly expressed during early chicken embryogenesis and that it is induced by retinoic acid treatment of chicken fibroblasts and myotubes in culture.