Delta Epsilon Research Articles

Sperm axoneme: a tale of tubulin posttranslation diversity.

Two microtubule-containing structures are assembled during spermiogenesis: a transient manchette and a stable axoneme. Both structures contain microtubules enriched in posttranslationally modified tubulins. Despite the existence of a spectrum of tubulin isotypes postulated by the multi-tubulin hypothesis, further extended by an elaborated array of posttranslational modifications, it is unknown how this diversity influences microtubule function. There is increasing evidence that different alpha beta-tubulin isotypes can affect the structure and function of microtubules. It is also becoming increasingly clear that eukaryotic cells encode other tubulin proteins expressed by the tubulin superfamily: gamma, delta epsilon, zeta eta, and FtsZ have been identified so far. Although the role of gamma-tubulin in the nucleation of microtubule assembly is well established, the function of delta-, epsilon-, zeta-, eta-, and FtsZ-tubulins is less understood. The members of the tubulin superfamilies found in spermatids include the alpha beta-tubulin dimer, in addition to gamma-tubulin in the centrosome, and delta-tubulin in the perinuclear ring region of the mouse spermatid manchette, the centrosome region, and flagellum. Posttranslational modifications in tubulin isotypes are predominant in the C-terminus exposed on the outside surface of the microtubule. This target site may influence the interaction of microtubule-associated proteins, including motor proteins, and therefore determine the functional specificity of tubulin isotypes. It remains to be determined whether other newcomers to the superfamily of tubulins contain sites prone to posttranslational modification.

Changes in mRNA expression of nicotinic acetylcholine receptor subunits during embryonic development of mouse masseter muscle.

Nicotinic acetylcholine receptors (nAChRs) switch from the embryonic-type (alpha 2 beta gamma delta subunits) to the adult-type (alpha 2 beta epsilon delta subunits), and disappear besides the neuromuscular junctions with the development of trunk and limb skeletal muscles. However, little is known about this process during the embryonic development of masseter muscle. To identify the time course of the nAChR transition from embryonic day (E) 11 to the newborn stage in mouse masseter muscle, we analyzed the expression level of delta, epsilon, and gamma subunit mRNAs by competitive polymerase chain reaction in combination with reverse transcription as well as distribution of delta subunit protein by immunohistochemistry. The nAChR delta subunit mRNA was initially detected at E11, showed an approximately 25-fold increase (p < 0.0001) between E11 and E17, and plateaued thereafter until the newborn stage. Immunostaining for delta subunit was observed in the whole portions of masseter myofibers at E17 and birth, suggesting that the nAChR elimination does not begin even at the newborn stage. The epsilon subunit mRNA initially appeared at E17, and increased in quantity by 144% (p < 0.0001) up to the newborn stage. The quantity of gamma subunit mRNA increased by approximately 240% (p < 0.0001) between E11 and E17, and then decreased by 22% (p < 0.05) from E17 value at the newborn stage. The beginning of the expression of the epsilon subunit mRNA was coincident with the beginning of the decrease in the quantity of the gamma subunit mRNA, suggesting that the nAChR subunit switch begins at E17.

Evolution of T cell receptor (TCR) alpha beta heterodimer assembly with the CD3 complex.

T cell antigen receptors (TCR) are composed of an antigen-recognizing unit, the TCRalpha beta heterodimer, and a signal transduction ensemble, the CD3 complex. Whereas mammals possess three CD3 dimers (delta epsilon, gamma epsilon, and zeta2), birds and amphibians have only two (delta/gamma-epsilon and zeta2). To understand evolutionary changes in TCR/CD3 assembly,a phylogenetic approach was employed to dissect the interaction of TCRalpha beta heterodimers with the CD3 components. While sheep and mouse TCRalpha and TCRbeta chains could replace the corresponding human chains in mutant human T cells to restore surface TCR/CD3 expression and function, chicken TCRalpha, TCRbeta and CD3delta/gamma chains were unable to replace the corresponding human chains in forming a chimeric TCR/CD3 complex. The inability of chicken TCR/CD3 components to replace the human molecules in T cells was found to result from the lack of interaction between chicken TCRalpha beta heterodimers and the human CD3 complex. In contrast, if no CD3 molecules are present (non-T cells), TCRalpha -TCRbeta chain pairing can take place in an apparently non-controlled way. Thus, the TCR-CD3 interactions have changed with the evolutionary divergence of two mammalian CD3gamma and CD3delta genes from a single prototypic chicken delta/gamma gene. Our data suggest that the structures in mammalian TCR.C regions, which distinguish between CD3delta and CD3gamma chains, have evolved with the appearance of two separate CD3delta and CD3gamma functions.

The neuroprotective agent ebselen modifies NMDA receptor function via the redox modulatory site.

Ebselen is a seleno-organic compound currently in clinical trials for the treatment of ischemic stroke and subarachnoid hemorrhage. Its putative mode of action as a neuroprotectant is via cyclical reduction and oxidation reactions, in a manner akin to glutathione peroxidase. For this reason, we have investigated the effects of ebselen on the redox-sensitive NMDA receptor. We have found that ebselen readily reversed dithiothreitol (DTT) potentiation of NMDA-mediated currents in cultured neurons and in Chinese hamster ovary (CHO) cells expressing wild-type NMDA NR1/NR2B receptors. In contrast, ebselen was unable to modulate NMDA-induced currents in neurons previously exposed to the thiol oxidant 5,5'-dithiobis(2-nitrobenzoic acid) (DTNB), or in CHO cells expressing a mutant receptor lacking the NR1 redox modulatory site, suggesting that ebselen oxidizes the NMDA receptor via this site. In addition, ebselen was substantially less effective in modifying NMDA responses in neurons exposed to alkylating agent N-ethylmaleimide (NEM) following DTT treatment. Ebselen also reversed DTT block of carbachol-mediated currents in Cos-7 cells expressing the alpha(2)beta delta epsilon subunits of the acetylcholine receptor, an additional redox-sensitive ion channel. Ebselen was observed to significantly increase cell viability following a 30-min NMDA exposure in cultured neurons. In contrast, other more typical antioxidant compounds did not afford neuroprotection in a similar paradigm. We conclude that ebselen may be neuroprotective in part due to its actions as a modulator of the NMDA receptor redox modulatory site.

Theoretical Calculation of Flory-Huggins and Scattering Interaction Parameters by Means of the Lattice Fluid Theory for PVME/PSD Blends

By fitting the spinodals of poly(vinyl methyl ether)/deuterated polystyrene (PVME/PSD) systems, the adjustable parameters epsilon (12)* and delta epsilon* in the Sanchez-Balasz lattice fluid (SBLF) theory could be determined for different molecular weights. According to these parameters, Flory-Huggins and scattering interaction parameters were calculated for PVME/PSD with different molecular weights by means of the SELF theory. From our calculation, Flory-Huggins and scattering interaction parameters are both Linearly dependent on the reciprocal of the temperature, and almost linearly on the concentration of PSD. Compared with the scattering interaction parameters, the Flory-Huggins interaction parameters decreased more slowly with an increase in the concentration for all three series of blends.

A new iron oxidase from a moderately thermophilic iron oxidizing bacterium strain TI‐1

Iron oxidase was purified from plasma membranes of a moderately thermophilic iron oxidizing bacterium strain TI-1 in an electrophoretically homogeneous state. Spectrum analyses of purified enzyme showed the existence of cytochrome a, but not cytochrome b and c types. Iron oxidase was composed of five subunits with apparent molecular masses of 46 kDa (alpha), 28 kDa (beta), 24 kDa (gamma), 20 kDa (delta), and 17 kDa (epsilon). As the molecular mass of a native enzyme was estimated to be 263 kDa in the presence of 0.1% n-dodecyl-beta-D-maltopyranoside (DM), a native iron oxidase purified from strain TI-1 seems to be a homodimeric enzyme (alpha beta gamma delta epsilon)(2). Optimum pH and temperature for iron oxidation were pH 3.0 and 45 degrees C, respectively. The K(m) of iron oxidase for Fe(2+) was 1.06 mM and V(max) for O(2) uptake was 13.8 micromol x mg(-1) x min(-1). The activity was strongly inhibited by cyanide and azide. Purified enzyme from strain TI-1 is a new iron oxidase in which electrons of Fe(2+) were transferred to haem a and then to the molecular oxygen.

Chirality inversion in the bilirubin molecular exciton.

The bichromophoric pigment bilirubin acts as a molecular exciton in its UV-visible and circular dichroism (CD) spectroscopy. In both polar and nonpolar solvents, an optically active analog, (beta R,beta 'R)-dimethylmesobilirubin-XIII alpha (1), exhibits intense bisignate CD Cotton effects in the region of its long wavelength UV-vis absorption near 400 nm: Delta epsilon(434)(max) + 337, Delta epsilon(389)(max) - 186 (CHCl(3)), and Delta epsilon(431)(max) + 285, Delta epsilon(386)(max) - 177 (CH(3)OH). However, introduction of an amine into a CHCl(3) solution of 1 causes the Cotton effect signs to become inverted, e.g., after addition of NH(3), Delta epsilon(433)(max) - 345, Delta epsilon(389)(max) + 243, and after addition of ethylene diamine, Delta epsilon(435)(max) - 420, Delta epsilon(390)(max) + 299. The sign inversions imply inversion of molecular chirality of the bilirubin and the phenomenon appears to be general for amines, including alpha,omega-diamines. 1,8-Diaminooctane was found to be more effective than longer or shorter chain analogs in producing CD sign inversion.

Frequency dependence of dynamic curvature effects on flow through coronary arteries.

The flow through a curved tube model of a coronary artery was investigated computationally to determine the importance of time-varying curvature on flow patterns that have been associated with the development of atherosclerosis. The entry to the tube was fixed while the radius of curvature varied sinusoidally in time at a frequency of 1 or 5 Hz. Angiographic data from other studies suggest that the radius of curvature waveform contains significant spectral content up to 6 Hz. The overall flow patterns were similar to those observed in stationary curved tubes; velocity profile skewed toward the outer wall, secondary flow patterns, etc. The effects of time-varying curvature on the changes in wall shear rate were expressed by normalizing the wall shear rate amplitude with the shear rate calculated at the static mean radius of curvature. It was found that the wall shear rate varied as much as 94 percent of the mean wall shear rate at the mid wall of curvature for a mean curvature ratio of 0.08 and a 50 percent change in radius of curvature. The effects of 5 Hz deformation were not well predicted by a quasi-static approach. The maximum values of the normalized inner wall shear rate amplitude were found to scale well with a dimensionless parameter equivalent to the product of the mean curvature ratio (delta), normalized change in radius of curvature (epsilon), and a Womersley parameter (alpha). This parameter was less successful at predicting the amplitudes elsewhere in the tube, thus additional studies are necessary. The mean wall shear rate was well predicted with a static geometry. These results indicate that dynamic curvature plays an important role in determining the inner wall shear rates in coronary arteries that are subjected to deformation levels of epsilon delta alpha > 0.05. The effects were not always predictable with a quasi-static approach. These results provide guidelines for constructing more realistic models of coronary artery flow for atherogenesis research.

Human neuronal threonine-for-leucine-248 alpha 7 mutant nicotinic acetylcholine receptors are highly Ca2+ permeable

A cDNA coding for the human neuronal nicotinic alpha7 receptor subunit with Leu-248 mutated to threonine was expressed in Xenopus oocytes. When activated by acetylcholine (AcCho), the receptors expressed generated currents that had low desensitization, linear current-voltage relation, and high apparent affinity for both AcCho and nicotine. These characteristics are similar to those already described for the chick threonine-for-leucine-247 alpha7 nicotinic AcCho receptor (nAcChoR) mutant (L247Talpha7). These properties were all substantially maintained when the human L248Talpha7 mutant was transiently expressed in human Bosc 23 cells. Simultaneous whole-cell clamp and fluorescence measurements with the Ca(2+) indicator dye Fura-2 showed that nicotine induced a Ca(2+) influx in standard 2 mM Ca(2+) solution. The average fractional Ca(2+) current flowing through L248Talpha7 nAcChoRs was 6.7%, which is larger than that flowing through muscle alpha(beta)epsilon(delta) nAcChoRs (4.1%). The relative Ca(2+) permeability, determined in oocytes in the absence of Cl(-), was measured from the shift in reversal potential caused by increasing the external Ca(2+) concentration from 1 to 10 mM. The human wild-type alpha7 nAcChoR was found to be more permeable than the L248Talpha7 mutant to Ca(2+). Our findings indicate that the Ca(2+) permeability of the homomeric alpha7 nAcChoR is larger than that of the heteromeric neuronal nicotinic receptors studied to date and is possibly similar to that of the N-methyl-D-aspartate subtype of brain glutamate receptors.

The CD3-γδε Transducing Module Mediates CD38-induced Protein-tyrosine Kinase and Mitogen-activated Protein Kinase Activation in Jurkat T Cells

We have examined the ability of the CD3-gamma delta epsilon and CD3-zeta signaling modules of the T cell receptor (TCR) to couple CD38 to intracellular signaling pathways. The results demonstrated that in TCR+ T cells that express the whole set of CD3 subunits CD38 ligation led to complete tyrosine phosphorylation of both CD3-zeta and CD3-epsilon polypeptide chains. In contrast, in TCR+ cells with a defective CD3-zeta association CD38 engagement caused tyrosine phosphorylation of CD3-epsilon but not of CD3-zeta. Despite these differences, in both cell types CD38 ligation resulted in protein-tyrosine kinase and mitogen-activated protein kinase activation. However, in cells expressing chimerical CD25-zeta or CD25-epsilon receptors or in a TCR-beta- Jurkat T cell line, CD38 ligation did not result in tyrosine phosphorylation of the chimeric receptors, or CD3 subunits, or protein-tyrosine kinase or mitogen-activated protein kinase activation. In summary, these results support a model in which CD38 transduces activating signals inside the cell by means of CD3-epsilon and CD3-zeta tyrosine phosphorylation. Moreover, these data identify the CD3-gamma delta epsilon signaling module as a necessary and sufficient component of the TCR/CD3 complex involved in T cell activation through CD38.

Molecular mechanisms in the TCR (TCR alpha beta-CD3 delta epsilon, gamma epsilon) interaction with zeta 2 homodimers: clues from a 'phenotypic revertant' clone.

The association between the TCRalphabeta-CD3gammaepsilondeltaepsilon hexamers and zeta2 homodimers in the endoplasmic reticulum (ER) constitutes a key step in TCR assembly and export to the T cell surface. Incompletely assembled TCR-CD3 complexes are degraded in the ER or the lysosomes. A previously described Jurkat variant (J79) has a mutation at position 195 on the TCR Calpha domain causing a phenylalanine to valine exchange. This results in a lack of association between TCRalphabeta-CD3gammaepsilondeltaepsilon hexamers and zeta2 homodimers. Two main hypotheses could explain this phenomenon in J79 cells: TCR-CD3 hexamers may be incapable of interacting with zeta2 due to a structural change in the TCR Calpha region; alternatively, TCR-CD3 hexamers may be incapable of interacting with zeta2 due to factors unrelated to either molecular complex. In order to assess these two possibilities, the TCR-CD3 membrane-negative J79 cells were treated with ethylmethylsulfonate and clones positive for TCR membrane expression were isolated. The characterization of the J79r58 phenotypic revertant cell line is the subject of this study. The main question was to assess the reason for the TCR re-expression. The TCR on J79r58 cells appears qualitatively and functionally equivalent to wild-type TCR complexes. Nucleotide sequence analysis confirmed the presence of the original mutation in the TCR Calpha region but failed to detect compensatory mutations in alpha, beta, gamma, delta, epsilon or zeta chains. Thus, mutated J79-TCR-CD3 complexes can interact with zeta2 homodimers. Possible mechanisms for the unsuccessful TCR-CD3 interaction with zeta2 homodimers are presented and discussed.

Modification of the T Cell Antigen Receptor (TCR) Complex by UDP-glucose:Glycoprotein Glucosyltransferase: TCR FOLDING IS FINALIZED CONVERGENT WITH FORMATION OF αβδεγε COMPLEXES

Most T lymphocytes express on their surfaces a multisubunit receptor complex, the T cell antigen receptor (TCR) containing alpha, beta, gamma, delta, epsilon, and zeta molecules, that has been widely studied as a model system for protein quality control. Although the parameters of TCR assembly are relatively well established, little information exists regarding the stage(s) of TCR oligomerization where folding of TCR proteins is completed. Here we evaluated the modification of TCR glycoproteins by the endoplasmic reticulum folding sensor enzyme UDP-glucose:glycoprotein glucosyltransferase (GT) as a unique and sensitive indicator of how TCR subunits assembled into multisubunit complexes are perceived by the endoplasmic reticulum quality control system. These results demonstrate that all TCR subunits containing N-glycans were modified by GT and that TCR proteins were differentially reglucosylated during their assembly with partner TCR chains. Importantly, these data show that GT modification of most TCR subunits persisted until assembly of CD3alpha beta chains and formation of CD3-associated, disulfide-linked alpha beta heterodimers. These studies provide a novel evaluation of the folding status of TCR glycoproteins during their assembly into multisubunit complexes and are consistent with the concept that TCR folding is finalized convergent with formation of alpha beta delta epsilon gamma epsilon complexes.

Epistatic interactions of deletion mutants in the genes encoding the F1-ATPase in yeast Saccharomyces cerevisiae.

The F1-ATPase is a multimeric enzyme (alpha3 beta3 gamma delta epsilon) primarily responsible for the synthesis of ATP under aerobic conditions. The entire coding region of each of the genes was deleted separately in yeast, providing five null mutant strains. Strains with a deletion in the genes encoding alpha-, beta-, gamma- or delta-subunits were unable to grow, while the strain with a null mutation in epsilon was able to grow slowly on medium containing glycerol as the carbon source. In addition, strains with a null mutation in gamma or delta became 100% rho0/rho- and the strain with the null mutation in gamma grew much more slowly on medium containing glucose. These additional phenotypes were not observed in strains with the double mutations: Delta alpha Delta gamma, Delta beta Delta gamma, Deltaatp11 Delta gamma, Delta alpha Delta delta, Delta beta Delta delta or Deltaatp11 Delta delta. These results indicate that epsilon is not an essential component of the ATP synthase and that mutations in the genes encoding the alpha- and beta-subunits and in ATP11 are epistatic to null mutations in the genes encoding the gamma- and delta-subunits. These data suggest that the propensity to form rho0/rho- mutations in the gamma and delta null deletion mutant stains and the slow growing phenotypes of the null gamma mutant strain are due to the assembly of F1 deficient in the corresponding subunit. These results have profound implications for the physiology of normal cells.

On the role of thymopoietins in cell proliferation. Immunochemical evidence for new members of the human thymopoietin family.

Thymopoietins (TMPOs) are a group of ubiquitously expressed nuclear proteins. They are suggested to play an important role in nuclear envelope organization and cell cycle control, as has been shown for lamina-associated polypeptides 2 alpha and beta, which are the rat homologs of human TMPOalpha and TMPObeta, respectively. The recent isolation and characterization of seven mouse TMPO mRNA transcripts named TMPO-alpha, beta, beta', gamma, epsilon delta and zeta, suggest that more than the three previously reported transcripts, alpha, beta, and gamma forms, may exist in humans. Here we report on the demonstration of putative human TMPOdelta and epsilon by immunoblotting of human cell lines using a newly prepared polyclonal antiserum against the common N-terminal region of TMPO. Furthermore, we prepared the first truly TMPO-beta-specific, affinity-purified polyclonal antiserum, using a part of the human analog of the beta-specific domain of mouse TMPO 220-259 for immunization. We showed that human TMPObeta is highly expressed in all cancerous cells tested, while hardly any cross-reactivities with other proteins could be detected. In contrast to the high expression of human TMPObeta in the cancer-derived neuroblastoma cell lines SK-N-MC and SMS-KAN, we found very low expression of human TMPObeta in low-proliferative nerve tissue. These data led us to the assumption that expression of TMPObeta may correlate with the occurrence of cancer, and therefore may serve as a new tumor marker, or even as a new target for cancer therapy.

Molecular mechanisms mediating synapse-specific gene expression during development of the neuromuscular junction.

Adult skeletal muscle locally expresses nicotinic acetylcholine receptors (nAChRs) at the neuromuscular junction by selective induction of their subunit-encoding genes (alpha beta epsilon delta) in endplate-associated myonuclei. Neuregulin/ARIA is a nerve-derived factor that is thought to be largely responsible for this local gene induction. Neuregulin/ARIA activates a Ras/MAP kinase signalling cascade, which ultimately induces nAChR epsilon-subunit gene expression via a 15 bp sequence that harbors a core Ets transcription factor binding site (GGA). Interestingly, this same sequence also appears to participate in extrajunctional repression of the epsilon-subunit gene. Muscle Ets 2 overexpression induces nAChR epsilon-subunit gene promoter activity, whereas a dominant/negative Ets blocks neuregulin-dependent induction. These results suggest that Ets transcription factors play a role in mediating synapse-specific and neuregulin-mediated motor neuron control of nAChR gene expression.

Bovine F1-ATPase covalently inhibited with 4-chloro-7-nitrobenzofurazan: the structure provides further support for a rotary catalytic mechanism.

F1-ATPase is the globular domain of F1F0-ATP synthase that catalyses the hydrolysis of ATP to ADP and phosphate. The crystal structure of bovine F1-ATPase has been determined previously to 2.8 A resolution. The enzyme comprises five different subunits in the stoichiometry alpha 3 beta 3 gamma delta epsilon; the three catalytic beta subunits alternate with the three alpha subunits around the centrally located single gamma subunit. To understand more about the catalytic mechanisms, F1-ATPase was inhibited by reaction with 4-chloro-7-nitrobenzofurazan (NBD-Cl) and the structure of the inhibited complex (F1-NBD) determined by X-ray crystallography. In the structure the three beta subunits adopt a different conformation with different nucleotide occupancy. NBD-Cl reacts with the phenolic oxygen of Tyr311 of the beta E subunit, which contains no bound nucleotide. The two other catalytic subunits beta TP and beta DP contain bound adenylyl-imidodiphosphate (AMP-PNP) and ADP, respectively. The binding site of the NBD moiety does not overlap with the regions of beta E that form the nucleotide-binding pocket in subunits beta TP and beta DP nor does it occlude the nucleotide-binding site. Catalysis appears to be inhibited because neither beta TP nor beta DP can accommodate a Tyr311 residue bearing an NBD group. The results presented here are consistent with a rotary catalytic mechanism of ATP synthesis and hydrolysis, which requires the sequential and concerted participation of all three catalytic sites. NBD-Cl inhibits the enzyme by preventing the modified subunit from adopting a conformation that is essential for catalysis to proceed.

Formalizing partial matching and similarity in case-based reasoning with a description logic

Our aim is to use a description logic including default delta and exception epsilon connectives as a formal framework for a case-based reasoning (CBR) system. This approach allows the retrieval of similar cases to be formalized. Subsumption and (sure, probable, typical, and exceptional) inheritance relations of the description logic are the foundations for the different retrieval tasks: abstracting the new case; classifying it in the index base (full and partial matching); evaluating similarity of the conceptual abstraction of the new case with the concepts of the index base, using conceptual preference criteria; and retrieving similar cases (instances) and applying instance preference criteria to order them. Our preference criteria are symbolic rather than numerical or those of fuzzy logic. Using description logic offers several advantages: the classification process can be used to retrieve similar cases, the formal properties and the efficiency of the system can easily be evaluated, and preference criteria are homogeneously based on the formal description logic framework. Moreover, preference criteria are independent of the knowledge and can thus be used in other applications.

ＮＫ細胞の増殖性疾患

Natural killer (NK) cells are a distinct non-T, non-B lineage of lymphocytes that mediate major histocompatibility complex-unrestricted cytotoxicity. Morphologically they are large granular lymphocytes, and phenotypically they commonly express CD16 and CD56 antigens, without expressing cell surface CD3. Although the developmental pathway of NK cells is not fully understood, they arise from CD34+ hematopoietic stem cells and, at least in part, differentiate in the bone marrow. They gain byctoplasmic CD3 gamma delta epsilon zeta antigens during maturation, and lose cytoplasmic CD3 gamma delta epsilon thereafter until the terminal maturation. Lymphoproliferative disorders of NK cells include NK cell-lineage granular lymphocyte-proliferative disorders (NK-GLPD), NK-cell lymphoma, and acute leukemia of NK-cell lineage. NK-GLPD are relatively rare. Most patients exhibit a chronic indolent clinical course, and do not require specific treatment. However, some patients exhibit an aggressive clinical course, and die of the disease despite extensive chemotherapy. This aggressive type NK-GLPD is caused by Epstein-Barr virus (EBV). Patients with NK-cell lymphoma are rare, and often exhibit necrotic lesion and angiocentric morphology. This tumor is mainly found in the nasal tract, but the true incidence of NK-cell lymphoma in nasal lymphomas is not known. Probably many lymphomas arising from the nasal cavity, but not from paranasal sinuses, are of NK-cell lineage. NK-cell lymphoma is also caused by EBV, and is resistant to combination chemotherapy. Acute leukemia of NK-cell lineage is very rare. Several cases of acute lymphoblastic leukemia and a single case of blast crisis of chronic myelogenous leukemia have been documented to have leukemic blasts characteristic of NK cells. However, the precise lineage and differentiation stage of the leukemic blasts have not been delineated.

Inversion walls in homeotropic nematic and cholesteric layers

We describe the experimental properties of metastable domains associated with the presence of an Inversion Wall (IW) and observed with homeotropically anchored nematic and cholesteric liquid crystals sandwiched between parallel glass plates. Such a distorted situation, stabilized by the application of an electric field parallel to the plates as described in reference [1], can also be obtained transiently either when filling a sample cell by capillarity or in some studies of directional solidification at the N-I interface [2]. The application of an electric field perpendicular to the plates with Delta epsilon 0 materials allows control of the reversal region thickness in the bulk of the sample and its associated birefringence. This IW can be stabilized in the particular case of low lateral extension globules in which the line tension of the looped disclination separating the pi wall regions from the homeotropic regions counterbalances the unfavourable bulk free energy. Particular attention is devoted to the defects of these walls, whose appearance using polarizing microscopy is similar to the umbilics of the Freedericksz transition. The structure of these 'four brush' defects is nevertheless here singular, corresponding to point defects of a 3D uniaxial nematic medium. In the case of a chiral nematic, these IW undergo a particular undulation instability which is also observed in 2D simulations.

Crystal structure of the epsilon subunit of the proton-translocating ATP synthase from Escherichia coli.

Proton-translocating ATP synthases convert the energy generated from photosynthesis or respiration into ATP. These enzymes, termed F0F1-ATPases, are structurally highly conserved. In Escherichia coli, F0F1-ATPase consists of a membrane portion, F0, made up of three different polypeptides (a, b and c) and an F1 portion comprising five different polypeptides in the stoichiometry alpha 3 beta 3 gamma delta epsilon. The minor subunits gamma, delta and epsilon are required for the coupling of proton translocation with ATP synthesis; the epsilon subunit is in close contact with the alpha, beta, gamma and c subunits. The structure of the epsilon subunit provides clues to its essential role in this complex enzyme. The structure of the E. coli F0F1-ATPase epsilon subunit has been solved at 2.3 A resolution by multiple isomorphous replacement. The structure, comprising residues 2-136 of the polypeptide chain and 14 water molecules, refined to an R value of 0.214 (Rfree = 0.288). The molecule has a novel fold with two domains. The N-terminal domain is a beta sandwich with two five-stranded sheets. The C-terminal domain is formed from two alpha helices arranged in an antiparallel coiled-coil. A series of alanine residues from each helix form the central contacting residues in the helical domain and can be described as an 'alanine zipper'. There is an extensive hydrophobic contact region between the two domains providing a stable interface. The individual domains of the crystal structure closely resemble the structures determined in solution by NMR spectroscopy. Sequence alignments of a number of epsilon subunits from diverse sources suggest that the C-terminal domain, which is absent in some species, is not essential for function. In the crystal the N-terminal domains of two epsilon subunits make a close hydrophobic interaction across a crystallographic twofold axis. This region has previously been proposed as the contact surface between the epsilon and gamma subunits in the complete F1-ATPase complex. In the crystal structure we observe what is apparently a stable interface between the two domains of the epsilon subunit, consistent with the fact that the crystal and solution structures are quite similar despite close crystal packing. This suggests that a gross conformational change in the epsilon subunit, to transmit the effect of proton translocation to the catalytic domain, is unlikely, but cannot be ruled out.