A Comparative Study on Selectivity of α-Conotoxins GI and ImI Using Their Synthetic Analogues and Derivatives

Comparative structure-function studies have been carried out for -conotoxin GI acting on nicotinic acetylcholine receptors (AChR) from mammalian muscles and from the electric organ of the Torpedo californica ray and for -conotoxin ImI, which targets the neuronal a7 AChR. A series of analogs has been prepared for this purpose: chemically modified derivatives, including a covalently linked dimer of GI, as well as analogs wherein one or several amino acid residues have been changed using solid-phase peptide synthesis. The activity of all compounds was assessed in competition with radioiodinated and/or tritiated -conotoxin GI for binding to the membrane-bound AChR of Torpedo californica. Binding of radioiodinated -conotoxin GI dimer was also monitored directly, revealing the largest, as compared to all other analogues, difference in the affinity between the two binding sites in the receptor (K_D 11 and 1200 nM). Comparison of binding data with the results of CD measurements point to important role of the spatial organization of the -conotoxin second loop in manifestation of their muscle or neuronal specificity.     

Molecular evolution of the nicotinic acetylcholine receptor: An example of multigene family in excitable cells

An extensive phylogenetic analysis of the nicotinic-acetylcholine-receptor subunit gene family has been performed by cladistic and phenetic methods. The conserved parts of amino acid sequences have been analyzed by CLUSTAL V and PHYLIP software. The structure of the genes was also taken in consideration. The results show that a first gene duplication may have occurred before the appearance of Bilateria. Three subfamilies then appeared: I-the neuronal -bungarotoxin binding-site subunits (7, 8); III-the neuronal nicotinic subunits (2–6, 2–4), which also contain the muscle acetylcholine-binding subunit (1); and IV—the muscle non- subunits (1, , ). The Insecta subunits (subfamily II) could be orthologous to family III and IV. Several tissular switches of expression from neuron to muscle and the converse can be inferred from the extant expression of subunits and the reconstructed trees. The diversification of the neuronal nicotinic subfamily begins in the stem lineage of chordates, the last duplications occurring shortly before the onset of the mammalian lineage. Such evolution parallels the increase in complexity of the cholinergic systems.Abbreviations -Bgt -bungarotoxin - ACh acetylcholine - MP maximum of parsimony - MYA million years ago - NJ neighbor-joining - nAChR nicotinic acetylcholine receptor Correspondence to: N. Le Novère     

Localization of a gene for human α-galactosidase B (=N-Acetyl-α-D-Galactosaminidase) on chromosome 22

Summary The localization of the structural gene for human -galactosidase B (=N-acetyl--galactosaminidase) was investigated by means of man-Chinese hamster and man-mouse somatic cell hybrids. The hybrid clones were analyzed for chromosomes and for a large number of known enzyme markers. The lysates of the hybrid cells were treated with Sepharose-coupled antihuman -galactosidase B and the activity of the adsorbed enzyme was measured on the Sepharose beads as N-acetyl--galactosominidase. The results show that the structural gene for human -galactosidase B is situated on chromosome 22, and that there is no structural relationship between human -galactosidase A and human -galactosidase B.     

Aldimine to ketoamine isomerization (Amadori rearrangement) potential at the individual nonenzymic glycation sites of hemoglobin a: Preferential inhibition of glycation by nucleophiles at sites of low isomerization potential

The relative roles of the two structural aspects of nonenzymic glycation sites of hemoglobin A, namely the ease with which the amino groups could form the aldimine adducts and the propensity of the microenvironments of the respective aldimines to facilitate the Amadori rearrangement, in dictating the site selectivity of nonenzymic glycation with aldotriose has been investigated. The chemical reactivity of the amino groups of hemoglobin A forin vitro reductive glycation with aldotriose is distinct from that in the nonreductive mode. The reactivity of amino groups of hemoglobin A toward reductive glycation (i.e., propensity for aldimine formation) decreases in the order Val-1(), Val-1(), Lys-66(), Lys-61(), and Lys-16(). The overall reactivity of hemoglobin A toward nonreductive glycation decreased in the order Lys-16(), Val-1(), Lys-66(), Lys-82(), Lys-61(), and Val-1(). Since the aldimine is the common intermediate for both the reductive and nonreductive modification, the differential selectivity of protein for the two modes of glycation is clearly a reflection of the propensity of the microenvironments of nonenzymic glycation sites to facilitate the isomerization reaction (i.e., Amadori rearrangement). A semiquantitative estimate of this propensity of the microenvironment of the nonenzymic glycation sites has been obtained by comparing the nonreductive (nonenzymic) and reductive modification at individual glycation sites. The microenvironment of Lys-16() is very efficient in facilitating the rearrangement and the relative efficiency decreases in the order Lys-16(), Lys-82(), Lys-66(), Lys-61(), Val-1(), and Val-1(). The propensity of the microenvironment of Lys-16() to facilitate the Amadori rearrangement of the aldimine is about three orders of magnitude higher than that of Val-1() and is about 50 times higher than that of Val-1(). The extent of nonenzymic glycation at the individual sites is modulated by various factors, such as thepH, concentration of aldotriose, and the concentration of the protein. The nucleophiles—such as tris, glycine ethyl ester, and amino guanidine—inhibit the glycation by trapping the aldotriose. The nonenzymic glycation inhibitory power of nucleophile is directly related to its propensity to form aldimine. Thus, the extent of inhibition of nonenzymic glycation at a given site by a nucleophile directly reflects the relative role ofpK _a of the site in dictating the glycation at that site. The nonenzymic glycation of an amino group of a protein is an additive/synergestic consequence of the propensity of the site to form aldimine adducts on one hand, and the propensity of its microenvironment to facilitate the isomerization of the aldimines to ketoamines on the other. The isomerization potential of microenvironment plays the dominant role in dictating the site specificity of the nonenzymic glycation of proteins.     

Ala99ser mutation in RIα Regulatory Subunit of protein kinase A causes reduced kinase activation by cAMP and arrest of hormone-dependent breast cancer cell growth

Expression of the RI regulatory subunit of protein kinase A type I is increased in human cancer cell lines, in primary tumors, in cells after transformation, and in cells upon stimulation of growth. Ala99 (the pseudophosphorylation site) of human RI was replaced with Ser (RI-p) for the structure-function analysis of RI. MCF-7 hormone- dependent breast cancer cells were transfected with an expression vector for the wild-type RI or mutant RI-p. Overexpression of RI-P resulted in suppression of protein kinase A type II, the isozyme of type I kinase, production of kinase exhibiting reduced cAMP activation, and inhibition of cell growth showing an increase in G0/G1 phase of the cell cycle and apoptosis. The wild-type RI overexpression had no effect on protein kinase A isozyme distribution or cell growth. Overexpression of protein kinase A type II regulatory subunit, RII, suppressed RI and protein kinase A type I and inhibited cell growth. These results show that the growth of hormone-dependent breast cancer cells is dependent on the functional protein kinase A type I.     

Ontogeny of estrogen receptor (ER) alpha and its co-localization with pituitary hormones in the pituitary gland of chick embryos

Estrogen is involved in regulating the development and hormone secretion of the anterior pituitary gland following its binding to estrogen receptors (ERs) expressed on pituitary cells. However, the pituitary is comprised of several cell types, and to date, there is no data about the specific cell types expressing ERs in embyonic chick pituitary. We therefore followed, by immunohistochemistry, the ontogeny of the pituitary ER alpha (ER), and the cell types expressing ER throughout chick embryo development. ER immunoreacitivity was restricted to the nuclei of pituitary cells. ER-immunopositive (ER⁺) cells were first detected at embryonic day 6.5 (E6.5), after which ER⁺ cells were consistently detected throughout the anterior pituitary gland, although the density of ER⁺ cells in the caudal lobe of the pars distalis was higher than that in the cephalic lobe. The proportion of ER⁺ cells in the pituitary was about 6% at E8.5; expression increased to 22% by E18.5 of gestation, with no additional change until hatching. Double-labeling of ER and pituitary hormones showed that the dominant cell types expressing ER were gonadotrophs immunopositive for luteinizing hormone (LH); the proportion of ER⁺ cells expressing LH increased throughout gestation and reached approximately 57% at hatching. About 2%–6% of thyroid-stimulating-hormone-immunopositive and 1%–2% prolactin-immunopositive cells expressed ER at later stages of embryonic development, but no growth-hormone-positive or adrenocorticotropic-hormone-positive cells expressed ER during the embryonic period. Thus, gonadotrophs are the main cell population expressing ER in the anterior pituitary gland of chick embryo, and ER is involved in regulating the development of the pituitary gland and the maturation of the hormone-secreting function.This work was supported by grants from the Natural Science Foundation for Outstanding Young Scientists of China (30325034) and the Natural Science Foundation of China (30170693, 30471264).     

Haemoglobin synthesis in 28 obligatory cases for α-thalassemia traits

Summary In the Far East two types of -thalassemia genes, namely -thalassemia₁ (-thal₁) and -thalassemia₂ (-thal₂) exist. Definite diagnosis of the -thal₁ and -thal₂ traits is very difficult because their hematological findings are minimally abnormal or normal. This study attempts to characterize the heterozygotes by hemoglobin chain synthesis in reticulocytes from obligatory cases of the -thal₁ and -thal₂ traits. Twelve parents of babies with hemoglobin Bart's hydrops fetalis (obligatory -thal₁ trait) had the mean total radioactivity / ratio of 0.76±SD 0.04, while that of 7 normal controls was 1.06±SD 0.04. The / globin chain ratios of 16 cases, who were either parents or offspring of patients with hemoglobin H disease, were found to segregate into 2 groups, i.e. 0.78±SD 0.03 (10 cases) and 0.92±SD 0.03 (6 cases), probably representing the -thal₁ and -thal₂ traits respectively. The hematological data of the first group showed definite hypochromic microcytic red cells, similar to thoseof the parents of the hydrops. The second group had significantly higher mean corpuscular hemoglobin than the first group, compatible with -thal₂ trait. Our globin chain synthesis study thus appears to be capable of discriminating normal, -thal₁ and -thal₂ traits.A preliminary report of the results was presented at the XV Congress of the International Society of Haematology, Israel, September, 1974.     

Comparison of the homologous carboxy-terminal domain and tail of α-crystallin and small heat shock protein

The C-terminal domain and tail, which is the most conserved region of the -crystallin/small heat shock protein (HSP) family, was obtained from rat A-crystallin, bovine B-crystallin and mouse HSP25. All three domains have primarily -sheet conformation and less than 10% of -helix, like the proteins from which they are derived. Whereas the C-terminal part of A-crystallin forms dimers or tetramers, the corresponding regions of B-crystallin and HSP25 form larger aggregates. The heat-protective activity, recently described for the -crystallin/small HSP family, is not retained in the C-terminal domain and tail. In the course of this study some differences with the previously published sequence of HSP25 were observed, and a revision is proposed.Abbreviations A2Dt residues 64–173 of rat -crystallin - B2Dt residues 70–175 of bovine B-crystallin - bp base pair - HSP2Dt residues 92–209 of HSP25 - HSP(s) heat shock protein(s) - HSP25 mouse small HSP - PCR polymerase chain reaction - PMSF phenylmethylsulfonyl chloride - SDS sodium dodecyl sulfate; polyacrylamide - WSF water-soluble fraction     

α-Thalassemia in Saudi Arabia: deletion pattern

Summary -Thalassemia exists at a high prevalence in several regions of Saudi Arabia. The restriction endonucleases Bam HI and BglII were used to investigate the molecular basis of deletion type of -thalassemia in 226 subjects from the eastern and 61 subjects from the northwestern regions of the country. The arrangements-/ and-/- were common. BglII digestion revealed the existence of rightward deletion in a majority of the cases. Leftward deletions, both homozygous and heterozygous, were also identified. Triple -gene arrangements -/ and -/- were observed at a low frequency in both regions.     

Control of glycoprotein synthesis: substrate specificity of rat liver UDP-GlcNAc:Manα3R β2-N-acetylglucosaminyl-transferase I using synthetic substrate analogues

UDP-GlcNAc: Man3R 2-N-acetylglucosaminyltransferase I (GlcNAc-T I; EC 2.4.1.101) is the key enzyme in the synthesis of complex and hybrid N-glycans. Rat liver GlcNAc-T I has been purified more than 25,000-fold (M _r 42,000). TheV _max for the pure enzyme with [Man6(Man3)Man6](Man3)Man4GlcNAc4GlcNAc-Asn as substrate was 4.6 µmol min^–1 mg^–1. Structural analysis of the enzyme product by proton nuclear magnetic resonance spectroscopy proved that the enzyme adds anN-acetylglucosamine (GlcNAc) residue in 1–2 linkage to the Man3Man-terminus of the substrate. Several derivatives of Man6(Man3)Man-R, a substrate for the enzyme, were synthesized and tested as substrates and inhibitors. An unsubstituted equatorial 4-hydroxyl and an axial 2-hydroxyl on the -linked mannose of Man6(Man3)Man-R are essential for GlcNAc-T I activity. Elimination of the 4-hydroxyl of the 3-linked mannose (Man) of the substrate increases theK _M 20-fold. Modifications on the 6-linked mannose or on the core structure affect mainly theK _M and to a lesser degree theV _max, e.g., substitutions of the Man6 residue at the 2-position by GlcNAc or at the 3- and 6-positions by mannose lower theK _M, whereas various other substitutions at the 3-position increase theK _M slightly. Man6(Man3)4-O-methyl-Man4GlcNAc was found to be a weak inhibitor of GlcNAc-T I.Abbreviations BSA Bovine serum albumin - Bn benzyl - Fuc, F l-fucose - Gal, G d-galactose - GalNAc, GA N-acetyl-d-galactosamine - Glc d-glucose - GlcNAc, Gn N-acetyl-d-glucosamine - HPLC high performance liquid chromatography - Man, M d-mannose - mco 8-methoxycarbonyl-octyl, (CH₂)₈ COOOCH₃ - Me methyl - MES 2-(N-morpholino)ethanesulfonate - NMR nuclear magnetic resonance - PMSF phenylmethylsulfonylfluoride - pnp p-nitrophenyl - SDS sodium dodecyl sulfate - T transferase - Tal d-talose - Xyl d-xylose; - {0, 2 + F} Man6 (GlcNAc2Man3) Man4GlcNAc4 (Fuc6) GlcNAc - {2, 2} GlcNAc2Man6 (GlcNAc2Man3) Man4GlcNAc4GlcNAc; M₅-glycopeptide, Man6 (Man3) Man6 (Man3) Man4 GlcNAc4GlcNAc-Asn Enzymes: GlcNAc-transferase I, EC 2.4.1.101; GlcNAc-transferase II, EC 2.4.1.143; GlcNAc-transferase III, EC 2.4.1.144; GlcNAc-transferase IV, EC 2.4.1.145; GlcNAc-transferase V, UDP-GlcNAc: GlcNAc2 Man6-R (GlcNAc to Man) 6-GlcNAc-transferase; GlcNAc-transferase VI, UDP-GlcNAc: GlcNAc6(GlcNAc2) Man6-R (GlcNAc to Man) 4-GlcNAc-transferase; Core 1 3-Gal-transferase, EC 2.4.1.122; 4-Gal-transferase, EC 2.4.1.38; 3-Gal-transferase, UDP-Gal: GlcNAc-R 3-Gal-transferase; blood group i 3-GlcNAc-transferase, EC 2.4.1.149; blood group I 6-GlcNAc-transferase, UDP-GlcNAc: GlcNAc3Gal-R (GlcNAc to Gal) 6-GlcNAc-transferase.     

High frequency of triplicated α-globin loci and absence or low frequency of α thalassemia in Polynesian Samoans

Summary Most of the population in certain areas of Melanesia have one -globin gene deletion ( thal₂). It is thought that the high frequencies of thal₂ in this population is due to a selective advantage given by malaria infection to carriers of thal₂. We are interested in neighboring Polynesia which, although adjacent to Melanesia, has always been free of malaria due to the absence of the vector anopheles. We studied 60 Polynesian Samoans and 150 Malaysians by restriction endonuclease gene mapping using Eco RI, Bam HI, and Bgl II and hybridization to ³²P-labeled -globin gene probe. Seven among the 60 (11.7%) Samoans had triplicated -globin loci type 1, while none had thal₂. On digestion with Bgl II the third -globin gene was found in an additional 3.7kb fragment in all seven Samoans with triplicated -globin loci, while digestion with Bam HI produced an abnormal elongated 18.2 kb fragment carrying -globin genes in addition to the normal 14.5 kb fragment. None of the Polynesian Samoans had thal₂ or thal₁. Only two of the Malaysians had triplicated -globin loci.     

Comparative Modulation by 3α,5α and 3β,5β Neurosteroids of GABA Binding Sites During Avian Central Nervous System Development

Neurosteroids are endogenous Central Nervous System (CNS) compounds which act mainly by allosteric modulation of the GABA_A receptor complex. The presence of a 3-hydroxyl group and a 5-hydrogen atom have been found to be essential structural requirements for biological activity in mammals. In the present work we report the enhancing activity on [³H]GABA binding to its receptor sites in chick optic lobe produced by progesterone metabolites 3-hydroxy,5-pregnan-20-one (3,5-P) and 3-hydroxy,5-pregnan-20-one (3,5-P). Both steroids were found able to enhance [³H]GABA binding along ontogeny, displaying a similar profile at early developmental stages, while in adulthood 3,5-P had greater potency (EC₅₀ 0.22 M) and enhancing effect (E_max: 122%). In adult synaptic membranes, the two compounds displayed a complex interaction with the GABA_A receptor, disclosed by a Schild plot with slope below one and an incomplete displacement of 3,5-P by its 3,5 isomer. Such complexity could be related to the steroidogenic profile in avian CNS, with 5-reduced progesterone metabolites present since early development, while 3,5-P is found only in adulthood. Bearing in mind differences between avian and mammalian steroidogenic profiles and the relevance of 5-steroids in early avian development, we propose that 3,5-P, instead of the classical potent 3,5-steroids, may be the endogenous modulator of GABAergic activity in developing avian brain.     

Evaluation of hydrophobicity versus chaperonelike activity of bovine alphaA- and alphaB-crystallin

Calf lens A-crystallin isolated by reversed-phase HPLC demonstrates a slightly more hydrophobic profile than B-crystallin. Fluorescent probes in addition to bis-ANS, like cis-parinaric acid (PA) and pyrene, show higher quantum yields or Ham ratios when bound to A-crystallin than to B-crystallin at room temperature. Bis-ANS binding to both A- and B-crystallin decreases with increase in temperature. At room temperature, the chaperone-like activity of A-crystallin is lower than that of B-crystallin whereas at higher temperatures, A-crystallin shows significantly higher protection against aggregation of substrate proteins compared to B-crystallin. Therefore, calf lens A-crystallin is more hydrophobic than B-crystallin and chaperone-like activity of -crystallin subunits is not quantitatively related to their hydrophobicity.     

Heterogeneity of the α-globin gene defects in German α-thalassemia affected families

Summary Analysis of -thalassemia syndromes in several German families revealed DNA deletion as well as nondeletion forms as the molecular basis for the defects. Thus, the -thalassemia haplotype was identified as the (–)^3.7 rightward deletion form, and the region of the putative recombination process generating such a deletion was further characterized. In addition three different ° haplotypes, (--)^MED, (--)^>26, and ()^T, could be detected using -and -globin gene-specific probes.     

Quantitative analysis of type IV collagen alpha chains in the basement membrane of human urogenital epithelium

Type IV collagen is a major component of the basement membrane (BM), which consists of six genetically distinct (IV) chains. In this study the expression of these six (IV) chains was demonstrated immunohistochemically. In addition, the 2(IV) and 5(IV) chains were analysed quantitatively by confocal laser scanning microscopy in human urogenital epithelial BM. The 1/2(IV) and 5/6(IV) chains were immunoreactive in the epithelial BM, whereas, 3/4(IV) chains were not. The quantitative analysis revealed that the amount of 2(IV) and 5(IV) chains differed in each urogenital epithelial BM. The content of 5(IV) chains in the epithelial BM of the bladder was differentially high, and that of the foreskin was differentially low. It is concluded that the elasticity of epithelial BM of the bladder may be structurally related to the high content of 5/6(IV) chains.     

Primary structure of alpha-globin chains from river buffalo (Bubalus bubalis L.) hemoglobins

Primary structure analysis of the four river buffalo -globin chains showed that haplotypes A and B differ from each other by a substitution at codon 64 that may encode Ala or Asn. The A haplotype encodes two -globin chains, ^I1 and ^II3, which differ at positions 129 and 131: ^I1 has 64 Ala, 129 Phe, 131 Asn; ^II3 has 64 Ala, 129 Leu, 131 Ser. The B haplotype encodes two -globin chains, ^I2 and ^II4, which differ at positions 10 and 11: ^I2 has 10 Ile, 11 Gln, 64 Asn; ^II4 has 10 Val, 11 Lys, 64 Asn. Apart from the Ala/Asn polymorphism at position 64, amino acid substitutions in allelic and nonallelic -globin chains seem to have arisen by single point mutations. Detection of electrophoretically silent mutations due to neutral amino acid substitutions and their influence on the isoelectric point are discussed. Furthermore, primary structures of river buffalo -globin chains are compared to other species of the Bovidae family to suggest evolutionary events that have characterized the amino acid substitutions of river buffalo hemoglobin.     

Expression of the mRNA encoding truncated PPARα does not correlate with hepatic insensitivity to peroxisome proliferators

Two alternatively spliced forms of human PPAR mRNA, PPAR1 and PPAR2, have been identified. PPAR1 mRNA gives rise to an active PPAR protein while PPAR2 mRNA gives rise to a form of PPAR which lacks the ligand-binding domain. PPAR2 is unable to activate a peroxisome proliferator response element (PPRE) reporter gene construct in transient transfection assays. Both PPAR1 and PPAR2 mRNA are present in human liver, kidney, testes, heart, small intestine, and smooth muscle. In human liver, PPAR2 mRNA abundance is approximately half that of PPAR1 mRNA; a correlation analysis of PPAR1 and PPAR2 mRNA mass revealed an r-value of 0.75 (n = 18). Additional studies with intact liver from various species, showed that the PPAR2/PPAR1 mRNA ratios in rat, rabbit, and mouse liver were less than 0.10; significantly lower than the 0.3 and 0.5 ratios observed in monkey and human livers, respectively. To determine if a high PPAR2/PPAR1 mRNA ratio was associated with insensitivity to peroxisome proliferators, we treated human, rat, and rabbit hepatocytes with WY14643, a potent PPARa activator, and measured acyl CoA oxidase (ACO) mRNA levels. Rat ACO mRNA levels increased markedly in response to WY14643 while human and rabbit hepatocytes were unresponsive. Thus, although the PPAR2/PPAR1 mRNA ratio is low in rabbits, this species is not responsive to peroxisome proliferators. Further studies with male and female rats, which vary significantly in their response to peroxisome proliferators, showed little difference in the ratio of PPAR2/PPAR1 mRNA. These data suggest that selective PPAR2 mRNA expression is not the basis for differential species or gender responses to peroxisome proliferators.     

Sialyltransferase activity in FR3T3 cells transformed withras oncogene: decreased CMP-Neu5Ac:Galβ1-3GalNAc α-2,3-sialyltransferase

We have investigated the activity of CMP-Neu5Ac:Gal\1-3GalNAc -2,3-sialyltransferase (EC 2.4.99.4) in FR3T3 cells transformed by the Ha-ras oncogene in which we have previously demonstrated the higher expression of the -galactosidase -2,6-sialyltransferase (EC 2.4.99.1) [21]. We demonstrate that the presence of the activatedras gene decreases the activity of this specific -2,3-sialyltransferase fourfold. According to the kinetic parameters and to mixing experiments, we can assume that this decreased enzymatic activity reflects a decrease in the number of activeO-glycan -2,3-sialyltransferase polypeptides inras-transformed cells. However, no change in the binding of Peanut agglutinin was observed on the cell surface ofras-transformed FR3T3 suggesting that no change in the sialylation ofO-glycan core 1 appeared in these cells, although the activity of the -2,3-sialyltransferase was decreased.Abbreviations -2,3-ST(O) CMP-Neu5Ac:Gal1-3GalNAc-R -2,3-sialyltransferase - -2,3-ST(N/O) CMP-Neu5Ac:Gal1-3/4GlcNAc-R -2,3-sialyltransferase - -2,6-ST(N) CMP-Neu5Ac:Gal1-4GlcNAc-R -2,6-sialyltransferase - -2,6-ST(O)I CMP-Neu5Ac:R-GalNAc(1-O)Ser -2,6-sialyltransferase - -2,6-ST(O)II CMP-Neu5Ac:Neu5Ac2-3Gal1-3GalNAc-R -2,6-sialyltransferase - ASFet asialofetuin - FR3T3 Fisher rat fibroblast - FRras Ha-ras-transfected FR3T3 fibroblasts - NaCl/P_i sodium phosphate 10mm, NaCl 0.15m, pH 7.4, buffer - pNp p-nitrophenol     

Molecular characterization of different ataxia telangiectasia T-cell clones

Summary Using in situ chromosomal hybridization we have mapped the gene for the T-cell receptor -chain in three different non-malignant T-cell clones occurring in ataxia telangiectasia. The constant region was translocated in each of the three clones. The variable region remained in its original position in two cases and was deleted in one clone which lost the derivative chromosome 14. We have therefore demonstrated that the T-cell receptor -gene is split in at least two of these translocations. To our knowledge, this is the first direct evidence of the involvement of a gene from the immunoglobulin superfamily in chromosomal rearrangements in ataxia telangiectasia.