bluuebunny/crossref_metadata_2025 huggingface dataset:
A small nuclear ribonucleoprotein is required for splicing of adenoviral early RNA sequences.
Authors: Yang V W , Lerner M R , Steitz J A , Flint S J
Published: May 2006

The size and structure of viral RNA species synthesized in nuclei isolated during the early phase of productive infection by adenovirus type 2 have been examined by electrophoresis in denaturing polyacrylamide cells and the nuclease S1 assay. The major products of transcription in vitro of early regions 1 and 2 in the adenoviral genome are processed RNA molecules that appear to be correctly spliced in isolated nuclei. Splicing of adenoviral RNA molecules is inhibited when nuclei are preincubated with antibodies from systemic lupus erythematosus patients that immunoprecipitate small nuclear ribonucleoprotein particles. The specificity of these antibodies suggests that ribonucleoprotein particles containing U1 RNA are required for splicing of the adenoviral RNA sequences we have examined.
Finite-time thermodynamics: Engine performance improved by optimized piston motion
Authors: Mozurkewich Michael , Berry R. S.
Published: May 2006

The methods of finite-time thermodynamics are used to find the optimal time path of an Otto cycle with friction and heat leakage. Optimality is defined by maximization of the work per cycle; the system is constrained to operate at a fixed frequency, so the maximum power is obtained. The result is an improvement of about 10% in the effectiveness (second-law efficiency) of a conventional near-sinusoidal engine.
Picosecond primary photoprocesses of bilirubin bound to human serum albumin.
Authors: Greene B I , Lamola A A , Shank C V
Published: May 2006

We measure the fluorescence quantum yield of bilirubin bound to its highest-affinity site on human serum albumin to increase from about 0.001 near room temperature to 0.5 at 77 K. The quantum yield for configurational (Z leads to E) photoisomerization about the meso double bonds concomitantly decreases from about 0.22 to less than 0.01 over the same temperature range in reciprocal relationship to the fluorescence yield. Transient absorption spectra recorded after excitation with a 0.5-ps pulse of 305-nm light decay with a lifetime of 19 +/- 3 ps at 22 degrees C and 35 +/- 7 ps at 2 degrees C. Bilirubin undergoes the same photoisomerization reaction in chloroform solution, in which a similar short-lived (17 +/- 3 ps at 22 degrees C) transient is observed. From these and other data we conclude that configurational isomerization of bilirubin is the predominant nonradiative pathway that competes with pigment fluorescence, that photoisomerization proceeds via a short-lived (much less than 18 ps) partially twisted excited-singlet-state intermediate, and that bilirubin remains relatively unihibited with respect to photoisomerization when bound to human serum albumin.
Structure of a B-DNA dodecamer: conformation and dynamics.
Authors: Drew H R , Wing R M , Takano T , Broka C , Tanaka S , Itakura K , Dickerson R E
Published: May 2006

The crystal structure of the synthetic DNA dodecamer d(CpGpCpGpApApTpTpCpGpCpG) has been refined to a residual error of R = 17.8% at 1.9-A resolution (two-sigma data). The molecule forms slightly more than one complete turn of right-handed double-stranded B helix. The two ends of the helix overlap and interlock minor grooves with neighboring molecules up and down a 2(1) screw axis, producing a 19 degrees bend in helix axis over the 11-base-pair steps of the dodecamer. In the center of the molecule, where perturbation is least, the helix has a mean rotation of 36.9 degrees per step, or 9.8 base pairs per turn. The mean propeller twist (total dihedral angle between base planes) between A . T base pairs in the center of the molecule is 17.3 degrees, and that between C . G pairs on the two ends averages 11.5 degrees. Individual deoxyribose ring conformations as measured by the C5'-C4'-C3'-O3' torsion angle delta, exhibit an approximately Gaussian distribution centered around the C1'-exo position with delta avg = 123 degrees and a range of 79 degrees to 157 degrees. Purine sugars cluster at high delta values, and pyrimidine sugars cluster at lower delta. A tendency toward 2-fold symmetry in sugar conformation about the center of the molecule is detectable in spite of the destruction of ideal 2-fold symmetry by the molecular bending. More strikingly, sugar conformations of paired based appear to follow a "principle of anticorrelation," with delta values lying approximately the same distance to either side of the center value, delta = 123 degrees. This same anticorrelation is also observed in other DNA and DNA . RNA structures.
A critique of the chemosmotic model of energy coupling.
Authors: Green D E
Published: May 2006

The chemosmotic model provides a framework for visualizing energy-coupled reactions (vectorial reaction sequences, membrane-dependent gradient formation, and charge separation of reacting species) and a mechanism for energy coupling (indirect coupling between the driving and driven reaction sequences mediated by a membrane potential or a protonmotive force). The mechanistic parameters of this model have been examined from four standpoints: compatibility with the experimental realities, supporting evidence that is unambiguous, compatibility with the enzymic nature of energy coupling, and the capability for generating verifiable predictions. Recent developments that have clarified the mechanism of ion transport, the nature of the protonic changes that accompany energy coupling, and the enzymic nature of energy coupling systems have made such an examination both timely and necessary. After weighing the available evidence, it has been concluded that the chemosmotic principle of indirect coupling has no basis in fact and that it is physically unsound in respect to the mechanism of energy coupling and enzymic catalysis.
Base substitution in an intervening sequence of a beta+-thalassemic human globin gene.
Authors: Spritz R A , Jagadeeswaran P , Choudary P V , Biro P A , Elder J T , deRiel J K , Manley J L , Gefter M L , Forget B G , Weissman S M
Published: May 2006

beta globin gene fragments from a patient with homozygous beta+-thalassemia have been cloned and subjected to restriction endonuclease, nucleotide sequence, and in vitro trancription analyses. Restriction endonuclease mapping of the cloned gene fragments revealed no deletions or other rearrangements, and transcription of the thalassemic gene appeared to be normal in vitro. However, nucleotide sequence analysis of the beta+-thalassemic gene fragments permitted identification of a single base change in the body of the small intervening sequence. This nucleotide change creates a sequence much like that of the 3' splice site of the small intervening sequence. The presence of a potential anomalous splicing site as a result of this base change suggests a mechanism for defective posttranscriptional processing of beta globin mRNA precursor molecules in beta+-thalassemia.
High molecular weight complex in human plasma between vitamin K-dependent protein S and complement component C4b-binding protein.
Authors: Dahlbäck B , Stenflo J
Published: May 2006

Protein S, a recently described vitamin K-dependent plasma protein, is shown to exist in two forms in plasma--free protein and in complex with C4b-binding protein. C4b-binding protein is involved in the regulation of the rate of complement activation. A major proportion of C4b-binding protein in plasma is in complex with protein S. The complex is a major and previously unrecognized component of the group of plasma proteins that adsorbs to barium citrate. The complex dissociates in the presence of NaDodSO4, indicating that C4b-binding protein and protein S are held together by noncovalent bonds. Uncomplexed C4b-binding protein was purified from the supernatant after barium citrate adsorption. On NaDodSO4/polyacrylamide gels without reduction, it appeared to have a slightly faster migration rate than the C4b-binding protein dissociated from the complex with protein S. After reduction, the subunits of the two forms of C4b-binding protein appeared to have identical molecular weights. Furthermore, there is an equilibrium between free and bound protein S in plasma. The role of protein S in the complex is unknown.
Unwinding of double-stranded DNA helix by dehydration.
Authors: Lee C H , Mizusawa H , Kakefuda T
Published: May 2006

Conformation changes of the double-stranded DNA helix in response to dehydration were investigated by monitoring, by agarose gel electrophoresis, the linking number of covalently closed circular DNA generated by ligation of linear DNA in the presence of different organic solvents or different temperatures. It was found that: (i) The DNA helix unwinds upon addition of certain organic solvents or elevation of temperature. (ii) The conformational change observed under the experimental conditions is a continuous process in response to the organic solvent concentration. (iii) The delta H of unwinding one linking of the DNA helix is constant at approximately 12.2 +/- 0.4 kcal/mol (1 kcal = 4.184 kJ); the corresponding delta S and d(delta S)/dn are 2nkR and 2kR, in which n is the relative equivalent linking number (referred to the state of delta S = 0 for unwinding) of the DNA, R is the gas constant, and k is equal to 1117/number of base pairs. The delta H, delta S, and d(delta S)/dn for unwinding i linkings are i X 12.2 kcal/mol, 2inkR, and 2ikR, respectively. (iv) d(delta S)/dn, like k, is inversely proportional to the number of base pairs in DNA. (v) Double-stranded DNAs of different chain lengths have average delta S = 35 cal/mol.K for unwinding one linking under the experimental conditions; this corresponds to 127 +/- 14 base pairs per "relative linking."
Light limitation of photosynthesis and activation of ribulose bisphosphate carboxylase in wheat seedlings
Authors: Perchorowicz John T. , Raynes Deborah A. , Jensen Richard G.
Published: May 2006

In limiting light the activation of ribulose-1,5-bisphosphate (Ru
P
2
) carboxylase [3-phospho-D-glycerate carboxylyase (dimerizing), EC 4.1.1.39] in leaf extracts of 7- to 8-day-old wheat seedlings changed proportionally with the photosynthetic rate of the intact plants. Higher rates of photosynthesis, induced by increasing irradiances, were accompanied by an increase in activation of the leaf Ru
P
2
carboxylase, while Ru
P
2
levels remained unchanged. The degree of activation varied from 20% to 60% of full activation at irradiances of 225-1650 μE/m
2
·s (photosynthetically active radiation; E = einstein, 1 mol of photons). Between 225 μE/m
2
·s and darkness, activation approached 50% while Ru
P
2
levels dropped more than 90%. During steady-state photosynthesis, levels of the substrate Ru
P
2
were 250-300 nmol/mg of chlorophyll in the leaves and were similar at all irradiances above 225 μE/m
2
·s (25% of light saturation). When velocities of the carboxylase in leaf extracts were corrected for CO
2
levels estimated to exist within the leaf, they compared favorably with the photosynthetic rates of the intact seedlings. Comparison of CO
2
exchange rate, Ru
P
2
level, and activation of the carboxylase indicates that light limitation of photosynthesis can be due to two factors: the availability of Ru
P
2
in dark to dim light and activation of the Ru
P
2
carboxylase in dim light and higher irradiances.
Origin of replication from Xenopus laevis mitochondrial DNA promotes high-frequency transformation of yeast.
Authors: Zakian V A
Published: May 2006

A specific fraction of chromosomal DNA from both yeast and a wide variety of other eukaryotes, but not from Escherichia coli, promotes high-frequency transformation in yeast. The plasmids containing these sequences are maintained as extra-chromosomal molecules in transformed cells. These results suggest that similar or identical sequences are used for the initiation of DNA replication in eukaryotes. To test this hypothesis, several foreign eukaryotic DNAs implicated directly or indirectly in the initiation of DNA replication have been examined for their ability to promote autonomous, extrachromosomal replication in yeast. Simian virus 40 DNA, amplified Xenopus laevis ribosomal DNA, X. laevis 5S ribosomal DNA, X. laevis mtDNA, and five different members of the Alu I family of human middle repetitive DNAs were cloned into the vector YIp5 and used to transform yeast. Of these DNAs, only Xenopus mtDNA promoted high-frequency transformation and extrachromosomal maintenance of YIp5 DNA. A 2.2-kilobase EcoRI fragment from the 17.4-kilobase mtDNA molecule was responsible for these activities. This fragment contains the sequence used for the initiation of replication in Xenopus mitochondria.
Elevated spontaneous mutation rate in Bloom syndrome fibroblasts.
Authors: Warren S T , Schultz R A , Chang C C , Wade M H , Trosko J E
Published: May 2006

The rates of spontaneous mutation to 6-thioguanine resistance were determined in fibroblasts derived from normal and two Bloom syndrome individuals (GM 2548 and GM 1492). Two methods were utilized to determine the rates. Method I obtained the spontaneous mutation rate from the increase in the mutation frequency of a cell population in logarithmic-phase growth over 10 days. The two Bloom syndrome strains had spontaneous mutation rates of 16 X 10(-6) and 17 X 10(-6) mutations per cell per generation, whereas two normal strains had rates of 1.5 X 10(-6) and 1.1 X 10(-6). Method II utilized fluctuation analysis to measure the rate of spontaneous mutation. This method resulted in rates of 19 X 10(-6) and 23 X 10(-6) mutations per cell per generation in Bloom syndrome cells, compared to rates of 4.6 X 10(-6) and 4.9 X 10(-6) in the control strains. These data suggest that Bloom syndrome may be a mutator mutation, a previously unrecognized phenomenon in humans, and that an elevated spontaneous mutation rate in vivo may be responsible for the clinical phenotype of primordial dwarfism and increased cancer incidence.
Differential effects of glucocorticosteroids on the functions of helper and suppressor T lymphocytes.
Authors: Bradley L M , Mishell R I
Published: May 2006

The effects of dexamethasone (Dex) on the functions of antigen-primed helper and suppressor T cells were studied in humoral immune responses in vitro. In doses equivalent to elevated physiologic concentrations, the suppressor T cell activity was abolished. In contrast, the helper T cell function was resistant to even pharmacologic concentrations of Dex. The apparent steroid resistance of the helper T cells was found to be mediated by the products of activated macrophages. While macrophage factors protected helper T cells from steroid inhibition, they did not prevent the effects of Dex on suppressor T cells. Because bacterial cell wall and membrane components are potent inducers of the factors that mediate steroid resistance of helper T cells, the combination of physiologically elevated levels of steroids and macrophage factors during acute infections may function to facilitate the expression of host immunity. However, the persistance of these conditions, as in chronic inflammation, may also contribute to the pathogenesis of autoimmunity by perturbing the balance of immune regulation by helper and suppressor T cells.
Biochemical stratagem for obligate parasitism of eukaryotic cells by Coxiella burnetii.
Authors: Hackstadt T , Williams J C
Published: May 2006

Coxiella burnetti, the etiologic agent of Q fever, is an oligate intracellular parasite of eukaryotes. Unlike the majority of successful bacterial parasites, which escape the bactericidal environment of the phagolysosome by various means, C. burnetii multiplies only in the phagolysosome. In view of the relatively harsh environment inhabited by C. burnetii, we have examined (i) the in vitro metabolism of glucose and glutamate by whole cells of C. burnetii under conditions designed to approximate the pH within the phagolysosome and (ii) the effect of manipulation of the phagolysosomal pH by lysosomotropic amines on the replication of C. burnetii in chicken embryo fibroblasts. The transport, catabolism, and incorporation of both glucose and glutamate were found to be highly stimulated by acidic conditions, whereas at pH 7.0 metabolism of these substrates was minimal. The transport processes were shown to be energy dependent and highly sensitive to inhibition by uncouplers of oxidative phosphorylation. Increasing the phagolysosomal pH of infected chicken embryo fibroblasts by use of the lysosomotropic agents chloroquine, methylamine, or ammonium chloride inhibited the multiplication of C. burnetii, thus demonstrating the in vivo requirement for the acidic conditions of the phagolysosome. This apparent dependence upon phagosome--lysosome fusion to generate pH conditions favorable to C. burnetii replication suggests a unique biochemical mechanism of parasite activation. A pathogenic mechanism based on regulation of microbial metabolism by H+-dependent stimulation of cell function is proposed.
Polarity of axoplasmic microtubules in the olfactory nerve of the frog.
Authors: Burton P R , Paige J L
Published: May 2006

Pieces of olfactory nerve of the bullfrog were extracted in a tubulin assembly buffer medium containing detergents. With incubation at 37 degrees C in such medium containing soluble tubulin, ribbons of protofilaments are formed on the surfaces of microtubules, with the ribbons curving in a clockwise or counterclockwise direction. The direction of hooking reflects the polarity of the microtubule. In nerve pieces oriented such that cross sections could be viewed toward the perikarya of the axons, over 90% of the ribbons on microtubules showed a clockwise orientation. When observers were looking toward the axonal terminals, most ribbons on microtubules showed a counterclockwise direction. In single axons in which ribbons appeared on all the contained microtubules, the ribbons showed a single directionality. The evidence suggests that microtubules in axons have a single polarity, probably reflecting their assembly from the perikarya outward through the axoplasm. If bidirectional transport is assumed in these axons, it is not reflected by the polarity of their microtubules, which may mean that the directionality of transport is provided by components other than microtubules.
Spin and wedge representations of infinite-dimensional Lie algebras and groups
Authors: Kac Victor G. , Peterson Dale H.
Published: May 2006

We suggest a purely algebraic construction of the spin representation of an infinite-dimensional orthogonal Lie algebra (sections 1 and 2) and a corresponding group (section 4). From this we deduce a construction of all level-one highest-weight representations of orthogonal affine Lie algebras in terms of creation and annihilation operators on an infinite-dimensional Grassmann algebra (section 3). We also give a similar construction of the level-one representations of the general linear affine Lie algebra in an infinite-dimensional “wedge space.” Along these lines we construct the corresponding representations of the universal central extension of the group

SL
n

(
k
[
t,t
-1
]) in spaces of sections of line bundles over infinite-dimensional homogeneous spaces (section 5).
Dexamethasone 21-mesylate: an affinity label of glucocorticoid receptors from rat hepatoma tissue culture cells.
Authors: Simons S S , Thompson E B
Published: May 2006

We recently described the biological properties of an alpha-keto mesylate derivative of cortisol, cortisol-Mes. Cortisol-Mes exhibited long-term antiglucocorticoid activity, but there was no firm evidence that this activity was irreversible or receptor-mediated. Here we report that dexamethasone mesylate (Dex-Mes), which is the alpha-keto mesylate derivative of the more active glucocorticoid dexamethasone, is a candidate for a steroid-specific affinity label of glucocorticoid receptors. Dex-Mes is relatively stable, like cortisol-Mes, but possesses greater whole-cell antiglucocorticoid activity. However, Dex-Mes also possesses partial agonist activity, which is expressed at somewhat higher concentrations of Dex-Mes than the antagonist activity. Dex-Mes is more efficient than cortisol-Mes in competing for dexamethasone binding to glucocorticoid receptors. Furthermore, Dex-Mes is effective at lower concentrations than cortisol-Mes in causing long-term apparently irreversible antiglucocorticoid effects in whole and broken cells. The cell-free effect of Dex-Mes is specifically prevented by coincubation with an excess of cortisol. These facts argue that the apparently irreversible effects of Dex-Mes are steroid mediated. [3H]Dex-Mes has been used to identify a glucocorticoid-specific, covalently labeled fraction on sodium dodecyl sulfate/polyacrylamide gels with a molecular weight of approximately 85,000. Thus Dex-Mes appears to have been established as an affinity label for glucocorticoid receptors.
Antihistaminics, local anesthetics, and other amines as antiviral agents.
Authors: Miller D K , Lenard J
Published: May 2006

A number of lipophilic amines of diverse chemical structure, including antihistaminics, local anesthetics, and chloroquine, were found to exhibit similar kinetics in inhibiting the infection of BHK cells by vesicular stomatitis virus. The inhibition occurred prior to both primary and secondary RNA transcription but following transfer from the cell surface to an intracellular site, presumed to be the lysosomes. A similar inhibition, by these agents, of infection by Sendai, influenza strain WSN, and Semliki Forest viruses suggested a lysosomal involvement in infection by these viruses as well.
Angiotensin II immunoreactivity coexists with renin in the juxtaglomerular granular cells of the kidney.
Authors: Celio M R , Inagami T
Published: May 2006

The multiple physiologic functions of angiotensin II(AII) are generally supposed to be mediated by the peptide generated in the blood circulation. In addition to this extracellular mechanism of AII formation, we have obtained immunohistochemical evidence for the intracellular synthesis of AII in the kidney. Rats were perfused with fixative, and paraffin sections of the kidneys were processed with antisera against renin (EC 3.4.99.19), AII, and other components of the renin--angiotensin system. Renin immunoreactivity was regularly observed in the epithelioid granular cells in the media of the afferent vessel of the glomerulus. AII immunoreactivity was found to coexist within the same cells. This observation points to an intracellular production of AII in the juxtaglomerular epitheloid granular cells. AII may then be released concomitantly with renin in the interstitial fluid and in the blood. The paracrine secretion of AII could exert a local regulatory influence on the tonus of the glomerular vessels.
Isolation and characterization of virus-specific double-stranded DNA from tissues infected by bean golden mosaic virus
Authors: Ikegami Masato , Haber Steve , Goodman Robert M.
Published: May 2006

A double-stranded (ds) DNA which may be a replication intermediate was isolated from bean (
Phaseolus vulgaris
L. “Top Crop”) leaves systemically infected with bean golden mosaic virus, a whitefly-transmitted plant virus with a genome of circular single-stranded (ss) DNA. The isolation method used phenol/chloroform extraction, hydroxyapatite column chromatography, and rate-zonal centrifugation. The dsDNA had sequences complementary to those of viral DNA. The guanine-plus-cytosine content was 35%, and the sedimentation coefficient in alkaline sucrose density gradients was similar to that of viral ssDNA. Digestion of the dsDNA by
Hha
I endonuclease produced fragments that corresponded exactly in number and size with those produced by complete digestion of circular viral ssDNA by
Hha
I, when the fragments were denatured and analyzed on polyacrylamide gels. The dsDNA molecule was a circular structure with one discontinuity in one strand; hybridization results suggest that some of a the dsDNA has a discontinuity in the viral strand and some has a discontinuity in the nonviral strand. On the basis of these structures for the dsDNA, a preliminary model for replication of viral DNA is discussed.
Production of immunologically active surface antigens of hepatitis B virus by Escherichia coli.
Authors: MacKay P , Pasek M , Magazin M , Kovacic R T , Allet B , Stahl S , Gilbert W , Schaller H , Bruce S A , Murray K
Published: May 2006

Several plasmids have been constructed which direct the synthesis of hepatitis B virus surface antigens in Escherichia coli either as the native polypeptide or fused to other plasmid encoded polypeptides. When injected into rabbits, extracts from bacteria carrying some of these plasmids induced the synthesis of antibodies to the antigens even though the extracts did not give satisfactory positive results in radioimmunoassay for them. Either the NH2-terminal segment or the COOH-terminal segment of the surface antigens alone was sufficient to elicit the immune response, but antibodies against the two segments showed different specificities. The results emphasize the value of an in vivo assay for the presence of antigens in crude cell extracts and illustrate the feasibility of this type of screening with laboratory animals.
Isolation of a cDNA clone for mouse urinary proteins: age- and sex-related expression of mouse urinary protein genes is transcriptionally controlled.
Authors: Derman E
Published: May 2006

A recombinant cDNA plasmid derived from mouse urinary protein (MUP) mRNA was isolated and used to determine the level of control of the developmentally regulated and the sex-linked expression of MUP genes by monitoring the transcription of MUP mRNA sequences in isolated liver nuclei. No transcription of MUP genes could be detected in liver nuclei of prepubescent animals whose livers do not contain measurable MUP mRNA. Transcription of MUP genes in the livers of adult male mice was 6-fold higher than in the livers of adult female mice, proportional to the difference in MUP mRNA concentrations. Transcriptional control mechanisms are therefore implicated as responsible for both the developmentally and the sex-linked changes in the expression of MUP genes.
Tropomyosin is decreased in transformed cells.
Authors: Hendricks M , Weintraub H
Published: May 2006

The steady-state level and synthesis of a pair of polypeptides of Mr 33,000 and 35,000 in chicken embryo fibroblasts (CEF) transformed by Rous sarcoma virus (RSV) are significantly decreased relative to normal CEF; however, the decrease is more pronounced in the case of the Mr 35,000 polypeptide. These polypeptides have been identified as the alpha and beta subunits of CEF tropomyosin by selective staining with tropomyosin antibody, two-dimensional gel electrophoresis, partial peptide analysis, and solubility properties. The decrease in tropomyosin is shown to be a transformation-specific phenomenon in that it does not occur after infection with a virus deleted in src sequences. Decreased synthesis of tropomyosin is also observed in quail cells transformed by MC29 (a retrovirus with a different onc gene than that in RSV) and also in chemically transformed quail cells. The decreased in tropomyosin is probably not a direct result of the disruption of the microfilament system in transformed cells because disruption of the microfilament system with trypsin or cytochalasin B in normal CEF does not lead to a decrease in tropomyosin synthesis. A decrease in tropomyosin in CEF after transformation may be a result of a pleiotropic effect that results in the transcriptional inactivation not only of the tropomyosin gene but also of the fibronectin and procollagen genes described by others.
Purification of chicken intestinal receptor for 1 alpha, 25-dihydroxyvitamin D3 to apparent homogeneity.
Authors: Simpson R U , DeLuca H F
Published: May 2006

The chicken intestinal 1 alpha, 25-dihydroxyvitamin D3 receptor-like protein has been purified to apparent homogeneity as determined by sodium dodecyl sulfate gel electrophoresis. The techniques employed for the purification include selective precipitation of the receptor by Polymin P (polyethyleneimine) and (NH4)2SO4 and batch adsorption to and selective elution from hydroxylapatite, followed by gel exclusion and DEAE-cellulose chromatography. Finally, the labeled receptor was eluted at a pH of approximately 6.0 on a chromatofocusing column. The protein was purified 6100-fold and the receptor was obtained in 9% yield.
Evidence for major histocompatibility complex restriction in transplantation immunity.
Authors: Silvers W K , Fleming H L , Naji A , Barker C F
Published: May 2006

Studies on the survival of histocompatibility-Y antigen (H-Y)-incompatible and skin-specific antigen (Skn)-incompatible skin grafts in mice, as well as those concerned with the survival of cultured parathyroid allografts in rats, indicate that grafts provoke a strong immune response only if they include donor macrophages (or Langerhans cells) or if major histocompatibility complex-compatible macrophages are available to react with cells bearing the foreign antigens.
Nascent polypeptide chains emerge from the exit domain of the large ribosomal subunit: immune mapping of the nascent chain.
Authors: Bernabeu C , Lake J A
Published: May 2006

The site of the nascent polypeptide chain as it leaves the ribosome has been localized on the "exit domain" of the Escherichia coli ribosome by using IgG antibodies directed against the enzyme beta-galactosidase (EC 3.2.1.23). Thus, a functional site has been mapped on intact 70S ribosomes. The exit site is on the large subunit, approximately 70 A from the interface between subunits and nearly 150 A from the central protuberance, the likely site of peptide transfer. It is adjacent to the region corresponding to the rough endoplasmic membrane binding region of the eukaryotic ribosome but distant from ribosomal components participating in mRNA recognition and polypeptide elongation (i.e., distant from the "translational domain"). These results, together with the protease protection experiments of others, provide evidence that the nascent protein chain probably passes through the ribosome in an unfolded, fully extended conformation.
Lenticular intermediate-sized filaments: biosynthesis and interaction with plasma membrane.
Authors: Ramaekers F C , Dunia I , Dodemont H J , Benedetti E L , Bloemendal H
Published: May 2006

Electron microscopical features of the lens fiber plasma membrane-cytoskeleton complex are suggestive of an intimate association between the intermediate-sized filaments (IF) and the lipid bilayer. Biochemical analysis of this complex reveals the occurrence of an appreciable amount of vimentin as a protein subunit of lenticular IF. Additional evidence for association between IF and membranes is provided by the observation that newly synthesized vimentin is associated with plasma membranes added to a reticulocyte lysate programmed with lens polyribosomes. Concomitantly alpha-crystallin polypeptide chains (alpha A2) are also found associated with the plasma membrane together with a hitherto unidentified 47-kilodalton protein. Once associated with the lipid bilayer, the vimentin polypeptide resists urea treatment, suggesting that it has become an integral constituent associated with part of the membrane.
Inhibitory effects of motilin, somatostatin, [Leu]enkephalin, [Met]enkephalin, and taurine on neurons of the lateral vestibular nucleus: Interactions with γ-aminobutyric acid
Authors: Chan-Palay Victoria , Ito Masao , Tongroach Pavich , Sakurai Masaki , Palay Sanford
Published: May 2006

Motilin, [Met]enkephalin, [Leu]enkephalin, somatostatin, taurine, γ-aminobutyric acid (GABA), and glycine were tested for their effects on Deiters neurons of the lateral vestibular nucleus in rabbits. Iontophoresis was carried out with multibarrelled micropipettes. All four peptides and three amino acids produced depression of neuron firing. No facilitatory responses were observed. The depressant action of each peptide when iontophoresed alone was dose-dependent and was rapid in onset and recovery. Their characteristic actions suggest the possibility of their independent roles as strong inhibitors, although the experimental paradigm does not allow conclusions about the individual potency of each peptide. When GABA was administered together with motilin, [Met]enkephalin, or somatostatin, the effects of the peptide and GABA were additive, producing depression greater than that with application of either substance alone. When GABA was applied in conjunction with [Leu]enkephalin, more complex interactions were observed. At low iontophoretic currents, [Leu]enkephalin antagonized the action of GABA, producing a depression less than that of GABA alone and of considerably slower onset, suggesting an additional modulatory effect. These observations support the conclusion that all substances tested are chemical mediators in the lateral vestibular nucleus and [Leu]enkephalin may be a neuromodulator as well. Because recent immunocytochemical studies indicate that Purkinje cells in the cerebellar cortex are chemically heterogeneous and exhibit immunoreactivity for motilin, taurine, the enkephalins, and somatostatin, as well as for the GABA-synthesizing enzyme glutamic acid decarboxylase, it is suggested that the Purkinje cell projections to vestibular and cerebellar nuclei are multimodal in their chemical coding. The uniformly depressant action of the peptides and amino acids reported here is consistent with earlier observations that Purkinje cells exert an inhibitory influence on the vestibular and central cerebellar nuclei.
Monoclonal antibody that specifically inhibits a human
M
r
52,000 plasminogen-activating enzyme
Authors: Kaltoft K. , Nielsen L. S. , Zeuthen J. , Dan[unk] K.
Published: May 2006

Monoclonal antibodies against a human plasminogen activator of
M
r
≈52,000 (HPA52) were derived by immunization of mice with an impure preparation of the enzyme (urokinase), subsequent hybridization of spleen cells with NSI-Ag4/1 myeloma cells, and cloning of the hybridomas. Selection of mice for hybridization and screening of hybridomas were based solely on direct inhibition of an enzymatic assay of the plasminogen activator with the impure enzyme preparation. A cloned hybridoma produced IgG1 antibodies that bound to and inhibited the enzymatic activity of HPA52 irrespective of whether the HPA52 was derived from urokinase or from human glioblastoma cells, whereas there was no inhibition of or binding to a plasminogen activator of
M
r
≈70,000 from human melanoma cells or a plasminogen activator of
M
r
≈36,000 that is a degradation product of HPA52 and present in urokinase. Nor did the anti-HPA52 IgG1 inhibit a murine plasminogen activator of
M
r
≈48,000 derived from sarcoma virus-transformed cells. By using affinity chromatography with columns of anti-HPA52 IgG1 bound to Sepharose, HPA52 was purified from urokinase to homogeneity as evaluated by NaDodSO
4
/polyacrylamide gel electrophoresis. This study demonstrates that inhibitory monoclonal antibodies against enzymes can be derived with the sole use of impure enzyme preparations and shows how such antibodies subsequently can be used for enzyme purification.
Sterol patterns of cultured zooxanthellae isolated from marine invertebrates: Synthesis of gorgosterol and 23-desmethylgorgosterol by aposymbiotic algae
Authors: Withers Nancy W. , Kokke W. C. M. C. , Fenical William , Djerassi Carl
Published: May 2006

Quantitative sterol compositions of cultured zooxanthellae isolated from various Pacific and Atlantic invertebrate hosts:
Zoanthus sociatus
(a zoanthid),
Oculina diffusa
(a scleractian coral),
Tridacna gigas
(a giant clam),
Melibe pilosa
(a nudibranch), and
Aiptasia pulchella
(a sea anemone) are reported. The results clearly demonstrate large differences in sterol patterns of zooxanthellae and that there is no obvious relationship between the taxonomic affiliation of the host and the sterol pattern of its isolated symbiont. The sterols of the zooxanthellae of
O. diffusa
(Cnidaria) and
T. gigas
(Mollusca) are qualitatively equivalent. Based on the structures of the two major free sterols synthesized by each alga, the zooxanthellae from different hosts were separated into three distinct groups. It was also found that an aposymbiotic alga can synthesize the unique marine sterols gorgosterol and 23-desmethylgorgosterol. Most of the sterols were identified by using mass spectroscopy and 360-MHz proton magnetic resonance. Spectroscopic data are reported for four novel sterols—(23,24
R
)-dimethyl-5α-cholest-(22
E
)-en-3β-o l, 23-methyl-5α-cholest-22
E
-en-3β-ol, cholesta-5,14-dien-3β-ol, and 4α-methyl-5α-cholesta-8(14)-24-dien-3β-ol.
Identification of cDNA clones coding for rat tyrosine hydroxylase antigen.
Authors: Lamouroux A , Faucon Biguet N , Samolyk D , Privat A , Salomon J C , Pujol J F , Mallet J
Published: May 2006

Five recombinant DNA plasmids have been constructed that contain structural gene sequences for rat tyrosine hydroxylase [TyrOHase; tyrosine 3-monooxygenase; L-tyrosine, tetrahydropteridine:oxygen oxidoreductase (3-hydroxylating), EC 1.14.16.2]. Rat pheochromocytoma PC 12 cell line, which contains relatively high levels of catecholamine-synthesizing enzymes, was used to purify RNA. TyrOHase cDNA clones were identified by screening 350 cDNA clones constructed from partially purified TyrOHase mRNA. A rapid and powerful screening of the recombinant clones by differential colony hybridization was possible because TyrOHase is a tissue-specific protein. The final selection relied on the ability of cDNA inserts to hybridize specifically to TyrOHase mRNA as judged by cell-free translation and immunoprecipitation. Blot hybridization analysis of polyadenylylated RNA from PC 12 cells indicated a major mRNA species of 1.9 kilobases. A species of the same size was identified from a human pheochromocytoma tumor, indicating a crossreactivity between rat TyrOHase cDNA and human TyrOHase mRNA.
Catabolism of low density lipoproteins by perfused rabbit livers: Cholestyramine promotes receptor-dependent hepatic catabolism of low density lipoproteins
Authors: Chao Yu-sheng , Yamin Ting-Ting , Alberts Alfred W.
Published: May 2006

Rabbits fed a wheat starch/casein diet develop a marked hypercholesterolemia accompanied by a decrease in the number of EDTA-sensitive binding sites on plasma membrane fractions of the liver for low density lipoproteins (LDL) and β-migrating very low density lipoproteins [Chao, Y.-S., Yamin, T.-T. & Alberts, A. W. (1982)
J. Biol. Chem.
, in press]. Inclusion of 1% cholestyramine resin in this diet prevents the increase in plasma cholesterol, increases the removal of LDL from plasma, and increases the number of hepatic plasma membrane LDL-binding sites. To determine the functional role of hepatic LDL-binding sites in the catabolism of LDL, we studied the catabolism of
125
I-labeled LDL (
125
I-LDL) by
in situ
perfused rabbit livers in a recirculating system. The rate of catabolism was measured from the increment of nonprotein-bound radioiodine in the perfusate. The receptor-dependent catabolism of LDL by the liver was calculated from the difference of hepatic catabolism of
125
I-LDL and catabolism of
125
I-labeled cyclohexanedione-modified LDL, which does not bind to LDL receptors. The data show that about 74% of LDL catabolized by perfused livers from chow-fed rabbits is through the receptor-dependent pathway and 26% is through the receptor-independent pathway. In rabbits fed a cholesterol diet, the hepatic catabolism of
125
I-LDL is reduced, and the receptor-dependent catabolism of
125
I-LDL is abolished. In rabbits fed the wheat starch/casein diet, the receptor-dependent catabolism of
125
I-LDL is reduced by 40% when compared with hepatic catabolism in chow-fed rabbits. Perfused livers from rabbits fed the wheat starch/casein diet supplemented with 1% cholestyramine show a 5,4-fold increase of receptor-dependent catabolism of
125
I-LDL when compared with that of livers from rabbits fed the wheat starch/casein diet alone. Thus, these studies demonstrate that the change in the number of rabbit hepatic membrane LDL receptors induced by dietary manipulation and drugs is correlated to the functional rate of removal of LDL by the liver.
Serum-free growth of normal and tumor mouse mammary epithelial cells in primary culture.
Authors: Imagawa W , Tomooka Y , Nandi S
Published: May 2006

Freshly isolated normal and tumor mouse mammary epithelial cells embedded within a collagen gel matrix undergo sustained growth when cultured for as long as 3 wk in a serum-free medium composed of a 1:1 (vol/vol) mixture of Hepesbuffered Ham's F12 and Dulbecco's modified Eagle's medium supplemented with insulin, epidermal growth factor (EGF), transferrin, bovine serum albumin fraction V, and cholera toxin. Of these additives, only insulin, EGF, and albumin are required for the growth of most normal cells. Albumin is not always an absolute requirement for growth but greatly enhances it. Lithium has been found to stimulate the growth of normal cells and can replace EGF. The collagen matrix culture system allows sustained growth of primary cultures of both normal and neoplastic mammary epithelium in serum-free conditions. This serum-free system will be useful in identifying and investigating the role of hormones, growth factors, and nutritional factors in regulating the growth of mammary epithelial cells.
Induction of human beta-interferon synthesis with poly(rI . rC) in mouse cells transfected with cloned cDNA plasmids.
Authors: Pitha P M , Ciufo D M , Kellum M , Raj N B , Reyes G R , Hayward G S
Published: May 2006

Human genomic DNA and plasmids carrying portions of the cDNA gene for human beta-interferon have been introduced into mouse Ltk- cells by cotransfection with a herpes simplex virus thymidine kinase (TK) gene. One plasmid contains 840 base pairs of human DNA complementary to pre-beta-interferon mRNA inserted into pBR322, whereas the other plasmids have hybrid genes containing only the 560-base pair coding region inserted under the transcriptional control of the TK promoter. Constitutive interferon production could not be detected in any of the mouse TK+ cell lines tested. Nevertheless, synthesis of interferon could be induced by poly(rI . rC) treatment in at least 16 of these cell lines, including clones transfected with genomic DNA, the beta-interferon cDNA, and the TK-beta-interferon cDNA hybrid gene. The interferon produced was specific for human cells and could be neutralized by antiserum against human beta-interferon. In contrast to human fibroblast cells, in which the synthesis of induced beta-interferon is transient, the poly(rI . rC)-induced TK+ lines continued to produce beta-interferon for prolonged periods of time and did not respond to superinduction conditions. Therefore, in transfected mouse cells, the coding DNA sequence from the human beta-interferon gene, without any of the adjacent 3' or 5' flanking human DNA sequences, was sufficient both to direct synthesis of biologically active product and to respond to the specific induction system that operates in human cells. However, the mechanism that switches off the synthesis of induced interferon in human cells appears not to operate in mouse cells transfected with beta-interferon cDNA.
Differing levels of dispersed repetitive DNA among closely related species of Drosophila.
Authors: Dowsett A P , Young M W
Published: May 2006

The genomic concentrations of certain middle repetitive DNA sequences vary considerably among closely related species of Drosophila. In fact, the chromosomes of D. melanogaster appear to carry approximately 3 times as much middle repetitive DNA as those of the sibling species D. simulans. Although most of the middle repetitive DNA of D. melanogaster consists of segments of "nomadic" DNA that occupy different dispersed chromosomal locations in different strains of flies, repeated DNA sequences recovered from the D. simulans genome are most often restricted to single chromosomal positions. Apparent differences in the total concentrations of middle repetitive DNA in the two species are most easily attributed to an approximately sevenfold difference in their dispersed repetitive and nomadic DNA contents. These differences may affect the relative mutation rates of these species or contribute to their reproductive isolation or both.
Human somatostatin I: sequence of the cDNA.
Authors: Shen L P , Pictet R L , Rutter W J
Published: May 2006

RNA has been isolated from a human pancreatic somatostatinoma and used to prepare a cDNA library. After prescreening, clones containing somatostatin I sequences were identified by hybridization with an anglerfish somatostatin I-cloned cDNA probe. From the nucleotide sequence of two of these clones, we have deduced an essentially full-length mRNA sequence, including the preprosomatostatin coding region, 105 nucleotides from the 5' untranslated region and the complete 150-nucleotide 3' untranslated region. The coding region predicts a 116-amino acid precursor protein (Mr, 12.727) that contains somatostatin-14 and -28 at its COOH terminus. The predicted amino acid sequence of human somatostatin-28 is identical to that of somatostatin-28 isolated from the porcine and ovine species. A comparison of the amino acid sequences of human and anglerfish preprosomatostatin I indicated that the COOH-terminal region encoding somatostatin-14 and the adjacent 6 amino acids are highly conserved, whereas the remainder of the molecule, including the signal peptide region, is more divergent. However, many of the amino acid differences found in the pro region of the human and anglerfish proteins are conservative changes. This suggests that the propeptides have a similar secondary structure, which in turn may imply a biological function for this region of the molecule.
Localization of allodeterminants on H-2Kb antigens determined with monoclonal antibodies and H-2 mutant mice.
Authors: Hämmerling G J , Rüsch E , Tada N , Kimura S , Hämmerling U
Published: May 2006

The topographic arrangement of antigenic determinants on the H-2Kb molecule was investigated by antibody competition studies with a series of monoclonal anti-Kb antibodies. For identification of amino acid residues participating in formation of allodeterminants H-2Kb mutant mice with defined amino acid substitutions were analyzed. The determinants were found to be located in at least two spatially separate clusters on the H-2Kb molecule. Determinants of one cluster are affected by mutations at amino acid positions 155 and 156, whereas determinants of a second cluster are modified by amino acid substitutions at positions 77 and 89. For a third cluster of determinants no relevant amino acid positions could be identified, but competition data indicate that this cluster is adjacent to the second one. The data suggest that the first two domains of H-2 antigens carry most allodeterminants.
Modulation of mRNA for microtubule-associated proteins during brain development.
Authors: Ginzburg I , Scherson T , Giveon D , Behar L , Littauer U Z
Published: May 2006

The heterogeneity of tau microtubule-associated proteins from rat brain is developmentally determined. Newborn rat brain contains two tau polypeptides (tau 0) with somewhat different molecular weights than the five tau components associated with microtubules from 12-day-old brain (tau 12). tau 0 and tau 12 are immunologically related and crossreact with antibodies against tau 12 proteins. Enrichment of the tau mRNA was achieved by prior hybridization of unfractionated poly(A)-containing mRNA to cDNA preparations containing tubulin and actin sequences. The remaining unhybridized mRNA was further fractionated by electrophoresis on methylmercury hydroxide agarose gels. Experiments involving cell-free translation of mRNA indicated that the major differences in the composition of tau proteins from newborn and developing brain are controlled at the mRNA level. The mRNA from newborn rat brain directed the synthesis of five tau proteins, two of which are specific for newborn brain, whereas the other three forms are characteristic of the developing brain. Thus, the appearance in newborn brain of mRNA species specific for three tau 12 forms precedes the phase of the synthesis of these proteins in the cell. By contrast, mRNA from 12-day brain directed the synthesis of four tau proteins specific for the developing brain, one of which is not synthesized by mRNA from newborn brain. None of the newborn tau 0 forms were synthesized with mRNA isolated from 12-day brain.