Colorimetric assays for evaluation of the mode of action of human immunodeficiency virus type 1 non-nucleoside reverse transcriptase inhibitors

Four non-nucleoside reverse transcriptase (RT) inhibitors, 9-CI-TIBO [(+)-S-4,5,6,7-tetrahydro-9- chloro-5-methyl-6-(3-methyl-2-butenyl)imidazo(4,5,1-jk)(1,4)- benzodiazepin-2(1H)-thione)], nevirapine (6,11-dihydro-11-cyclopropyl-4-methyl-dipyrido[2,3-b:2',3'-e]-[1,4]di azepin- 6-one), MSA-300 (N-[cis-2-(2-hydroxy-3-acetyl-6-methoxy-phenyl)-cyclopropyl]-N'- (5-chloropyrid-2-yl)-thiourea) and delavirdine ¿1-(5-methanesulphonamido-1H-indol-2-yl-carbonyl)-4-[3- (1-methylethylamino)pyridinyl]piperazine¿ were analysed for the mode of action of their inhibition of human immunodeficiency virus type 1 (HIV-1) RT in three different assays utilizing a 96-well microtitre plate format, with solid-phase conjugated poly(rA) as template. These were: (i) direct RT assay, for determination of IC50 values of RT inhibitors; (ii) RT template/primer binding inhibition (BIC) assay, for measuring the effect of various substances on the RT activity binding to template/primer; (iii) RT protein ELISA, for measuring RT protein binding to template/primer with a monoclonal antibody reactive against a peptide in the RNase H region. MSA-300 and delavirdine gave the lowest IC50 values, ranging from 0.17 microM to 0.24 microM for MSA-300 and from 0.12 microM to 0.38 microM for delavirdine, whereas higher IC50 values of approximately 20 microM were obtained for 9-CI-TIBO at all primer concentrations. None of the non-nucleoside substances had inhibiting effects on the binding of template, primer, or template/primer to RT protein. Their inhibition of RT activity was not due to prevention of RT binding to template/primer. TIBO, nevirapine and delavirdine bound to RT reversibly, and they bound more tightly to RT template/primer ternary than to RT template binary complex. MSA-300 showed a comparatively high affinity for the enzyme. The utility of the three assays in relation to screening and analysis of RT inhibitory substances is discussed.

[An application of genetic algorithms to the analysis of EXAFS spectrum]

Extended X-ray absorption fine structure (EXAFS) has been extensively used in the structural study in recent years. But the current methods of analysis EXAFS spectrum is difficult and tedious,demanding either very similar standard samples or the initial parameters near the solution. In this paper, a new technique Genetic Algorithms (GAs), was applied to the analyzing of the EXAFS spectrum,and two spectra of CU samples were investigated by the method. It was found that reasonable results can be obtained by the method only with limiting the initial parameters to a broad range. Comparing the results with those obtained by EXCURVE88, the fitting is superior, and the parameters are reasonable. Therefore, it is proved that the GAs may be a high performance method for the analyzing of the EXAFS spectra.

[Application of wavelet transform to the isolation of EXAFS oscilations from experiment data]

It is of significant importance to isolate lambda(k) form the total absorption cofficient data micro(E) for the analysis of EXAFS spectrum. Generally, least-squares procedure of polynomial spline or B spline was used for removing the smooth sbsorption background, which has been proved to be effective. But it suffers in that the trial of knot points is time-consuming and it is poor in reproducibility. In this paper, a new chemometrics method--wavelet transform analysis was used to separate the lambda(k) and background absorption from micro(E) and it is proved that the technique is a very good method for the analysis of EXAFS spectrum.

Construction and characterization of monomeric tryptophan repressor: a model for an early intermediate in the folding of a dimeric protein

Tryptophan repressor (TR) from Escherichia coli is a homodimer whose highly helical subunits intertwine in a complex fashion. A monomeric version of Trp repressor has been constructed by introducing a pair of polar amino acids at the hydrophobic dimer interface. Analytical ultracentrifugation was used to show that the replacement of leucine at position 39 with glutamic acid results in a monomer/dimer equilibrium whose dissociation constant is 1.11 x 10(-)4 M at 25 degrees C and pH 7.6. Tryptophan fluorescence, both near- and far-UV circular dichroism, and NMR spectroscopies demonstrated that, at the micromolar concentrations where the monomer predominates, secondary and tertiary structure are present. Hydrophobic dye-binding experiments showed that nonpolar surface is accessible in the monomeric form. The urea-induced equilibrium unfolding of monomeric L39E TR was monitored by circular dichroism, fluorescence, and absorbance spectroscopies. Coincident transitions show that the urea denaturation process follows a simple two-state model involving monomeric native and unfolded forms. The free energy at standard state in the absence of denaturant was estimated to be 2.37 +/- 0.15 kcal mol-1, and the sensitivity of the unfolding transition to denaturant, the m value, was 0.86 +/- 0.04 kcal mol-1 M(urea)-1 at pH 7.6 and 25 degrees C. The thermal denaturation transition occurred over a broad temperature range, suggesting either that the enthalpy change is small or that intermediates may exist. Kinetic studies showed that both the refolding and unfolding of the monomer were complete in the mixing dead time of stopped-flow CD and fluorescence spectroscopy, 5 ms. These structural, thermodynamic, and kinetic results are very similar to those previously reported for an early, monomeric intermediate in the folding of the wild-type TR dimer [Mann, C. J., & Matthews, C. R. (1993) Biochemistry 32, 5282-5290]. The construction of a stable, monomeric form of TR that strongly resembles a transient folding intermediate should provide useful insights into the nature of the early events in the folding of TR.

The evolutionary pressure to inactivate. A subclass of synaptotagmins with an amino acid substitution that abolishes Ca2+ binding

Synaptotagmin I is a Ca2+-binding protein of synaptic vesicles that serves as a Ca2+ sensor for neurotransmitter release and was the first member found of a large family of trafficking proteins. We have now identified a novel synaptotagmin, synaptotagmin XI, that is highly expressed in brain and at lower levels in other tissues. Like other synaptotagmins, synaptotagmin XI has a single transmembrane region and two cytoplasmic C2-domains but is most closely related to synaptotagmin IV with which it forms a new subclass of synaptotagmins. The first C2-domain of synaptotagmin I (the C2A-domain) binds phospholipids as a function of Ca2+ and contains a Ca2+-binding site, the C2-motif, that binds at least two Ca2+ ions via five aspartate residues and is conserved in most C2-domains (Shao, X., Davletov, B., Sutton, B., Südhof, T. C., Rizo, J. R. (1996) Science 273, 248-253). In the C2A-domains of synaptotagmins IV and XI, however, one of the five Ca2+-binding aspartates in the C2-motif is substituted for a serine, suggesting that these C2-domains do not bind Ca2+. To test this, we produced recombinant C2A-domains from synaptotagmins IV and XI with either wild type serine or mutant aspartate in the C2-motif. Circular dichroism showed that Ca2+ stabilizes both mutant but not wild type C2-domains against temperature-induced denaturation, indicating that the mutations restore Ca2+-binding to the wild type C2-domains. Furthermore, wild type C2A-domains of synaptotagmins IV and XI exhibited no Ca2+-dependent phospholipid binding, whereas mutant C2A-domains bound phospholipids as a function of Ca2+ similarly to wild type synaptotagmin I. These experiments suggest that a class of synaptotagmins was selected during evolution in which the Ca2+-binding site of the C2A-domain was inactivated by a single point mutation. Thus, synaptotagmins must have Ca2+-independent functions as well as Ca2+-dependent functions that are selectively maintained in distinct members of this gene family.

Expression of an Epstein-Barr-virus receptor and Epstein-Barr-virus-dependent transformation of human nasopharyngeal epithelial cells

The human herpes virus Epstein-Barr (EBV) is clearly associated with African Burkitt's lymphoma and the undifferentiated form of nasopharyngeal carcinoma (NPC). EBV has been implicated in other types of lymphoma, as well as in some human breast cancers. However, its route of entry into epithelial cells is incompletely understood. We report here evidence that there is no gene alteration in the SCR 1 and 2 exons of EBVR/CR2 in human embryonic nasopharyngeal epithelial (HENE) cells and NPC cells and that SCR 1 and 2 mRNA could be detected in HENE cells, different differentiated NPC cell lines and well-differentiated NPC biopsies. None of 15 cases of poorly differentiated NPC cryosections has SCR 1 and 2 mRNA. We also provide evidence that transformation of HENE cells results from exposure to infectious EBV and that transformation is dependent on the presence of phorbol ester. These data suggest that expression of SCR 1 and 2 of EBVR/CR2 may be associated with replication of EBV and support the notion of direct infection and transformation of human nasopharyngeal epithelial cells destined to evolve into the carcinoma by EBV through EBVR/CR2.

Gallstones and their chemical types in relation to serum lipids and apolipoprotein levels

OBJECTIVE

To determine the profile of lipidemia in patients with gallstones and the characteristics of lipidemia in different kinds of gallstone in gallbladder for predicting high risk subjects predisposed to gallstone formation by means of some serum parameters.

METHODS

Serum lipids and apolipoproteins levels in 47 patients with stone in gallbladder (stone group) were compared with those in 19 inpatients without stone (control group). The characteristics of lipidemia in different kinds of gallbladder stones were also compared.

RESULTS

Serum apolipoprotein (Apo) A1, C2 and E levels in the stone group significantly increased as compared with the control group (P < 0.01), but there were no statistically significant differences in TC, TG, LDL-C, HDL-C, HDL-C/TC, LDL-C/HDL-C, Apo A2, B and C3 and Apo A1/Apo B levels between the stone and control groups (P > 0.05). Increased levels of serum LDL-C and Apo B and the LDL-C/HDL-C ratio (P < 0.05) were characterized as an index of cholesterol stones, while elevated levels of serum TG and Apo C2 (P < 0.05) as an index of pigment stones.

CONCLUSIONS

Serum apolipoproteins might be more sensitive parameters as compared with serum lipids in distinguishing patients with stones from subjects without stones. There are different profiles of serum lipids and apolipoproteins in different chemical types of gallbladder stones.

Interactional cloning of the 84-kDa major outer dense fiber protein Odf84. Leucine zippers mediate associations of Odf84 and Odf27

The study of mammalian sperm tail outer dense fibers (ODF), a structure of unknown function, is hampered by the insoluble nature of ODF proteins and the availability of only one cloned component, Odf27. We report here the first use of the Odf27 leucine zipper as bait in a yeast two-hybrid screen to isolate a novel testis-specific protein whose interaction with Odf27 depends critically on the Odf27 leucine zipper. We find that the novel gene, 111-450, encodes a product that localizes to ODF as determined by fluorescence microscopy and immunoelectron microscopy and that the gene 111-450 product is identical to the major ODF protein, Odf84. Interestingly, Odf84 contains two C-terminal leucine zippers, and we demonstrate that all leucine residues in the upstream leucine zipper are required for interaction with Odf27, demonstrating the strategic validity of our approach. The use of the yeast screening approach to isolate leucine zipper containing proteins should be useful in other systems, and our findings have implications for ODF structural models.

Synaptotagmin-syntaxin interaction: the C2 domain as a Ca2+-dependent electrostatic switch

Synaptotagmin I is a synaptic vesicle protein that is thought to act as a Ca2+ sensor in neurotransmitter release. The first C2 domain of synaptotagmin I (C2A domain) contains a bipartite Ca2+-binding motif and interacts in a Ca2+-dependent manner with syntaxin, a central component of the membrane fusion complex. Analysis by nuclear magnetic resonance spectroscopy and site-directed mutagenesis shows that this interaction is mediated by the cooperative action of basic residues surrounding the Ca2+-binding sites of the C2A domain and is driven by a change in the electrostatic potential of the C2A domain induced by Ca2+ binding. A model is proposed whereby synaptotagmin acts as an electrostatic switch in Ca2+-triggered synaptic vesicle exocytosis, promoting a structural rearrangement in the fusion machinery that is effected by its interaction with syntaxin.

[Screening of antiviral agents from medicinal herbs by means of Hepadnaviruses models]

The antiviral study of 21 Chinese medicinal herbs was carried out in vitro and in vivo. The extracts of phyllanthus urinarin and polygonum cuspidatum exhibite obvious effects on duck hepatitis B virus and human hepatitis B virus, while the extract of Eclipta alba showed limited inhibition on HBV DAN polymerase.

Self-interaction of the major 27-kilodalton outer dense fiber protein is in part mediated by a leucine zipper domain in the rat

The RT7 gene is exclusively expressed in spermatids and encodes the 27-kDa major outer dense fiber (ODF) protein ODF27. Analysis of its amino acid structure had indicated the presence of a putative leucine zipper dimerization motif in the N-terminus and the presence of PCX repeats in the C-terminus. We had previously shown that the ODF27 N-terminal fragment can interact with full-length ODF27. We have used two different methods to analyze this interaction further. First we used fusion proteins between glutathione S-transferase (GST) and ODF27-derived fragments to show that the N-terminal half of ODF27 as well as the first 100 amino acids can interact with ODF27. A fusion protein consisting of GST and the ODF27 leucine zipper did not interact with ODF27. We found that the ODF27 C-terminal half can also interact with ODF27. The yeast two-hybrid method was next employed to analyze these interactions in vivo. We found that 1) N-terminal fragments containing the leucine zipper interact with the ODF27 N-terminus, but not with its C-terminus, 2) deletion of the leucine zipper abolished this interaction, and 3) the PCX repeats are involved in the self-interaction of the ODF27 C-terminus. The detected self-associations are weak. To analyze the molecular weight of in vitro-translated ODF27, we carried out gel filtration experiments. They show that at low concentrations, a fraction of ODF27 proteins exists as multimers while the rest are monomers whose shape deviates considerably from that of globular proteins. Our results identify regions in the N- and C-termini of ODF27 involved in self-interactions and suggest that in ODF, where high protein concentrations prevail, ODF27 can self-interact.

Sequence and expression of the murine Hoxd-3 homeobox gene

Murine Hoxd-3 (Hox 4.1) genomic DNA and cDNA and Hoxa-3 (Hox 1.5) cDNA were cloned and sequenced. The homeodomains of Hoxd-3 and Hoxa-3 and regions before and after the homeodomain are highly conserved. Both Hoxa-3 and Hoxa-3 proteins have a proline-rich region that contains consensus amino acid sequences for binding to Src homology 3 domains of some signal transduction proteins. Northern blot analysis of RNA from 8- to 11-day-old mouse embryos revealed a 4.3-kb species of Hoxd-3 RNA, whereas a less abundant 3.0-kb species of Hoxd-3 RNA was found in RNA from 9- to 11-day-old embryos. Two species of Hoxd-3 poly(A)+ RNA, 4.3 and 6.0 kb in length, were found in poly(A)+ RNA from adult mouse kidney, but not in RNA from other adult tissues tested. Hoxd-3 mRNA was detected by in situ hybridization in 12-, 14-, and 17-day-old mouse embryos in the posterior half of the myelencephalon, spinal cord, dorsal root ganglia, first cervical vertebra, thyroid gland, kidney tubules, esophagus, stomach, and intestines.

Bipartite Ca2+-binding motif in C2 domains of synaptotagmin and protein kinase C

C2 domains are found in many proteins involved in membrane traffic or signal transduction. Although C2 domains are thought to bind calcium ions, the structural basis for calcium binding is unclear. Analysis of calcium binding to C2 domains of synaptotagmin I and protein kinase C-beta by nuclear magnetic resonance spectroscopy revealed a bipartite calcium-binding motif that involves the coordination of two calcium ions by five aspartate residues located on two separate loops. Sequence comparisons indicated that this may be a widely used calcium-binding motif, designated here as the C2 motif.

[In vitro transformation of human embryonic nasopharyngeal epithelial cells with Epstein-Barr virus]

EBV from B95-8 cells were used to infect directly the human embryonic nasopharyngeal epithelial (HENE) cells in vitro.

RESULTS

Primary HENE cells treated with EBV did not have a significantly increased colony-forming rate in soft agarose, while cells that were treated with EBV in combination with tumor promotor 12-O-tetradecanoylphorbol-13 acetate (TPA) showed a marked increase in colonyforming rate from 0-5 cells to 20-40 colonies per 10,000 cells. (2) HENE cells treated with inactivated (56 degrees C for 30 minutes) virus, in spite of adding TPA at the same time, did not significantly increase agarose colony forming rate; (3) HENE cells treated with TPA after EBV exposure for a week had significantly increased colony forming rate in soft agarose, while the cells exposed to EBV after using TPA treatment did not. In addition, EBV BNLF1 (LMP) fragment in HENE cells treated with EBV or EBV+TPA was detected by polymerase chain reaction using specific oligonucleotide primer. Only HENE cells treated with EBV+TPA presented positive band in aragose gel electrophoresis. The results suggest that transformation of EBV on HENE cells depends on infectious virus and an intact viral genome. TPA not only can promote the transformation, but also promote EBV's entering HENE cells.

Changes in M-CSF-like activity during chicken embryonic development

We have established a method for separation of chicken bone-marrow cells using Percoll density gradient centrifugation, and have developed a new method for determining chicken M-CSF-like activity employing a liquid culture. Using this method, we determined M-CSF-like activities in egg yolk, chorioallantoic fluid (CAF) and amniotic fluid (AmF), and studied the effects of M-CSF on development of chicken embryos. M-CSF-like activity in egg yolk was at a high level before the incubation of the egg; it began to decrease on the third day of incubation and rapidly decreased on the fourth day, and no significant activity was detected after the tenth day of incubation. M-CSF-like activity in CAF was very low, and it exhibited almost no change during development. No M-CSF-like activity was detected in AmF throughout the experimental period.

Crystal structure of the V alpha domain of a T cell antigen receptor

The crystal structure of the V alpha domain of a T cell antigen receptor (TCR) was determined at a resolution of 2.2 angstroms. This structure represents an immunoglobulin topology set different from those previously described. A switch in a polypeptide strand from one beta sheet to the other enables a pair of V alpha homodimers to pack together to form a tetramer, such that the homodimers are parallel to each other and all hypervariable loops face in one direction. On the basis of the observed mode of V alpha association, a model of an (alpha beta)2 TCR tetramer can be positioned relative to the major histocompatibility complex class II (alpha beta)2 tetramer with the third hypervariable loop of V alpha over the amino-terminal portion of the antigenic peptide and the corresponding loop of V beta over its carboxyl-terminal residues. TCR dimerization that is mediated by the alpha chain may contribute to the coupling of antigen recognition to signal transduction during T cell activation.

Characterization of the slow folding reactions of trp aporepressor from Escherichia coli by mutational analysis of prolines and catalysis by a peptidyl-prolyl isomerase

Escherichia coli trp aporepressor (TR) is a highly helical, dimeric protein whose folding has been shown to involve three phases whose relaxation times range from 200 ms to 50 s at 25 degrees C and pH 7.6 [Gittelman, M. S., & Matthews, C. R. (1990) Biochemistry 29, 7011-7021]. All three phases are urea and protein concentration independent below 3 M urea, suggesting that cis/trans proline isomerization might limit the folding of TR under these conditions. This hypothesis was tested by measuring the sensitivity of the folding reaction to site-directed mutagenesis and to cyclophilin, a peptidyl-prolyl isomerase. Each of the four proline residues in TR was replaced singly as well as simultaneously, and the effects on the folding mechanism were assessed. All of these mutants, including the version lacking prolines (des-Pro TR), retain three slow, denaturant-independent folding phases similar to those observed for wild-type TR. However, the pattern of catalysis of the two slower folding phases in wild-type and mutant TRs by cyclophilin shows that cis/trans isomerization of the Thr44/Pro45 peptide bond can limit folding in proteins containing Pro45. The observation of three urea-independent, slow folding phases in des-Pro TR demonstrates that proline isomerization is not solely responsible for this complex folding behavior. Other types of isomerization or conformational rearrangement reactions appear to limit the folding of this dimeric protein under strongly folding conditions.

[The relationship between serum lipids, apolipoproteins level and bile lipids level, chemical type of stone]

To pick up serum high risk lithogenic factors predisposing one to gallstone formation and protective factors against gallstone formation in gallbladder. We compared serum lipid and apolipoprotein level of patients with gallbladder stone (stone group) with that of patients without gallbladder stone (control group). The correlation between serum lipid, apolipoprotein level and bile lipid level, cholesterol saturated index (CSI), characteristics of lipidemia in different kinds of gallbladder stones were studied. The results showed that the increase of serum Apo A1, C2 and E level in the stone group was more significant than in the control group. But there was no statistical significance in TC, TG, LDL-C, HDL-C, Apo A2, B, C3 level between the stone and control groups. These results suggested that serum apolipoproteins perhaps are more sensitive parameters than serum lipids in distinguishing patients with stones from those without stones. There were different profiles of serum lipid and apolipoproteins in different chemical types of gallbladder stones. Increased level in serum LDL-C, Apo B and ratio of LDL-C/HDL-C were characterized by an index for cholesterol stone, otherwise that in serum TG and Apo C2 an index for pigment stones. There was a positive correlation between serum total cholesterol (TC) or Apo B, C2, C3 and cholesterol amount or CSI in gallbladder bile. Therefore, TC, Apo B, C2, C3 could be considered as high risk lithogenic factors. A positive correlation existed between serum HDL-C and lecithin in gallbladder or common bile duct (CBD) bile as well as between HDL-C and bile acids in CBD bile. Thus, HDL-C might be a protective factor against gallstone formation in gallbladder.

Duck hepatitis B virus model for screening of antiviral agents from medicinal herbs

The effects of the extracts of 20 Chinese medicinal herbs and an antiviral drug foscarnet on duck hepatitis B virus (DHBV) endogenous DNA polymerase (DNAp) activity were compared. The extracts of P. urinaria showed a dose-dependent inhibition on DHBV DNAp. And those of other herbs showed little inhibition effect. Primary duck hepatocyte (PDH) cultures were used for evaluating effects of the extract of P. urinaria, foscarnet and acyclovir (ACV) on DHBV, and all the drugs or the extracts showed inhibition of DHBV DNA replication. Furthermore, in vivo trials were carried out. Peking ducks infected with LJ-76 strain of DHBV were treated with the extract of P. urinaria or ACV and compared with placebo treated control ducks. The treatment results in the loss or reduction of circulating viral DHBV DNA and DHBsAg.

[Determination of piperylpiperidine in wuwei qingzhuo powder by reversed phase HPLC]

A quantitative method has been developed for the determination of piperylpiperidine in Wuwei Qingzhuo powder by reversed phase HPLC. The average recovery is 102.0% (RSD = 0.46%) and lowest detection concentration 0.03 microgram/ml. The linear range of piperylpiperidine is 1.875-30 micrograms/ml, r = 0.9999.

Analysis of nucleotide pools in human lymphoma cells by capillary electrophoresis

Capillary electrophoresis is applied to determine nucleotide pool levels in human Burkitt lymphoma cells. The analysis was performed on a 65 cm x 50 microns I.D. Ucon-coated column with on-column UV detector. The method requires only nanoliters of sample and a simple sample preparation procedure. Over 12 nucleotides were separated and quantitated with high resolution and reproducibility. The whole capillary electrophoretic separation time was only 35 min. These results demonstrate that capillary electrophoresis provides a useful and easy way to analyze nucleotide pools in cells.

Capillary electrophoresis of nucleotides on ucon-coated fused silica columns

Ucon-coated columns have been used to isolate nucleotides, such as ribonucleotides, deoxyribonucleotides, and pyridine nucleotides, by capillary zone electrophoresis. This neutral, hydrophilic column coating (Ucon) significantly reduced macromolecule adsorption and electroosmotic flow, which provides the maximum resolution of the nucleotides separated under moderate buffer conditions (pH about 5-6). The relative standard deviations of the nucleotides were less than 1%. Low minimum detectable concentrations (about 2-8 microM) and quantities (about 70-360 fmol) of the ribonucleotides were obtained. A qualitative and quantitative analysis of the ribonucleotides in hybridoma cell extracts shows the applicability of the developed methodology for the determination of intracellular nucleotide pools under the desirable buffer conditions.

[An improved colorimetric assay for chicken M-CSF like activity using chicken bone marrow cells cultured on micro-culture plates]

The role of M-CSF in the process of mammalian development has been drawing attention. Unlike mammalian embryonic development, in which M-CSF is supplied by the maternal body, avian embryonic development begins and proceeds under the influence of a certain amount of M-CSF present in each fertilized egg, and its concentration can be experimentally controlled while observing the embryo's developmental state. Apart from this fact, aves provide us with many other advantages in the study of embryonic development. It is, however, not easy to separate multipotent hematopoietic stem-cell fractions from avian bone marrow. In addition, because a macrophage colony forming assay in soft agar, though it has been widely used, requires a large number of cells and a long culture period, the method of assay is not adequate for the sensitive detection of M-CSF activity in small scale samples. We have established a method for the depletion of nucleated erythrocytes from chicken bone marrow cell suspensions using percoll density gradient centrifugation, and have also developed a new method for determining chicken M-CSF-like activity employing a liquid culture. In this method, a 100 microliters aliquot of fractionated hematopoietic stem cells, 1 x 10(5), was placed in a well of 96-well flat-bottom culture plate, 100 microliters of sample was then added to each well, and the uptake of neutral red was measured after 4 days of culture. These procedures represent a simple and sensitive means of detecting M-CSF-like activity in chicken serum of x60 to x32 dilutions.(ABSTRACT TRUNCATED AT 250 WORDS)

Crystallization and preliminary X-ray diffraction study of a bacterially produced T-cell antigen receptor V alpha domain

A recombinant form of the variable domain of the alpha chain of a murine T-cell receptor specific for the N-terminal nonapeptide of myelin basin protein in association with the major histocompatibility complex class II I-Au molecule has been crystallized in a form suitable for X-ray diffraction analysis. This protein was secreted into the periplasmic space of Escherichia coli cells and affinity-purified using a nickel chelate adsorbent. The crystals are orthorhombic, space group P2(1)2(1)2, with unit cell dimensions a = 97.7 A, b = 79.6 A, c = 30.4 A and diffract to beyond 2.2 A resolution. The ability to crystallize a T-cell receptor domain produced in bacteria strongly suggests that the periplasmic space can provide a suitable environment for the correct in vivo folding of this class of antigen recognition molecules.