bluuebunny/crossref_metadata_2025 huggingface dataset:
Quantitation of muscle-specific mRNAs by using cDNA probes during chicken embryonic muscle development in ovo.
Authors: Saidapet C R , Munro H N , Valgeirsdóttir K , Sarkar S
Published: May 2006

The emergence of abundant-class mRNAs specific for contractile muscle proteins and their distribution between polysomal and free mRNP fractions were studied in skeletal muscle excised from chicken embryos during the transition from myoblasts (day 9) to myotubes (day 18). Muscle-specific cDNA was selectively prepared by hybridizing cDNA to template RNA (polysomal poly(A)+ mRNA) from day-14 embryos followed by isolation of the abundant class, which represents approximately 20% of total mRNA. The specificity of the cDNA probe for this class was confirmed by the differential degree of hybridization to cytoplasmic RNA from cultured myotube and myoblast cells and by its inability to hybridize with mRNA from nonmuscle cells such as liver. Except for muscle from day-9 embryos, the concentrations of the abundant-class muscle-specific mRNAs were higher in polysomes than in free mRNP fractions. Furthermore, the levels of these mRNAs in polysomes increased 12-fold from day 9 (myoblast) to day 14 (intermediate) with a further 3.6-fold increase from day 14 to day 18 (myotube). In contrast to this 45-fold net increase in the polysomal level of these mRNAs from day 9 to day 18, the levels in the free mRNP fraction showed only a 3-fold decrease during this period. Because the amount of mRNA lost from the mRNP fraction is much less than the net increase in the polysome fraction, mRNP does not serve as a reservoir of untranslated muscle-specific mRNA for transfer to polysomes. Consequently, the emergence of muscle-specific polysomal mRNA for contractile proteins during myogenesis in ovo appears to be regulated primarily by transcriptional control.
Direct modification of the membrane adenylate cyclase system by islet-activating protein due to ADP-ribosylation of a membrane protein.
Authors: Katada T , Ui M
Published: May 2006

GTP and isoproterenol activation of adenylate cyclase [ATP pyrophosphate-lyase (cyclizing), EC 4.6.1.1] in washed membranes prepared from C6 gliomas cells was enhanced by incubation with islet-activating protein, one of the pertussis toxins, if the incubation mixture was supplemented with NAD and ATP. The action of the protein was observed immediately after its addition and increased progressively in magnitude as the protein concentration or the incubation time increased. There was simultaneous incorporation of radioactivity from the ADP-ribose moiety of variously labeled NAD into the membrane protein with a molecular weight of 41,000. We conclude that islet-activating protein enhances receptor-mediated GTP-induced activation of membrane adenylate cyclase as a result of ADP-ribosylation of a membrane protein, probably one of the components of the receptor-adenylate cyclase system.
Identification of ColE1 DNA sequences that direct single strand-to-double strand conversion by a phi X174 type mechanism.
Authors: Nomura N , Low R L , Ray D S
Published: May 2006

A DNA single-strand initiation sequence, named rriA (called rri-1 previously), was detected in the origin region (Hae II fragment E) of the ColE1 plasmid [Nomura, N. & Ray, D. S. (1980) Proc. Natl. Acad. Sci. USA 77, 6566-6570]. Another site, called rriB, has been found on the opposite strand of Hae II fragment C. Both rriA and rriB (i) direct conversion of chimeric M13 phage single-stranded DNA to parental replicative form DNA in vivo by a rifampicin-resistant mechanism that is dependent on the dnaG and dnaB gene products, (ii) provide effector sites of dATP hydrolysis by primosomal protein n', and (iii) require the same primosomal proteins as phi X174 DNA for directing the in vitro conversion that rriA is the DNA sequence that determines the mechanism of lagging strand synthesis of ColE1 DNA and that the mechanism of discontinuous synthesis involves the primosomal proteins utilized in the in vitro conversion of phi X174 single strands to the double-stranded replicative form.
Neutrino mass, proton decay, and neutron oscillations as crucial tests of unification models (A Review)
Authors: Marshak R. E.
Published: May 2006

Several crucial tests of three popular unification models (of strong, electromagnetic, and weak interactions) are described. The models are
SU
(5) and
SO
(10) at the grand unification theory (GUT) level and
SU
(4)

C

×
SU
(2)

L

×
SU
(2)

R

at the partial unification theory (PUT) level. The tests selected for discussion are the finiteness of the neutrino mass in the electron volt region, the decay of protons into antileptons in the range of 10
31±
yr, and the detectability of neutron oscillations at all. The PUT group can also be tested by establishing the existence of four generations of quarks and leptons.
Old and new relics in cosmology (A Review)
Authors: Wilczek Frank
Published: May 2006

Deep connections have been found between cosmology and elementary particle physics.
In vitro methylation of the hamster adenine phosphoribosyltransferase gene inhibits its expression in mouse L cells.
Authors: Stein R , Razin A , Cedar H
Published: May 2006

The effect of DNA methylation on the expression of the hamster adenine phosphoribosyltransferase (aprt) gene in mouse cells has been examined. This gene was methylated in vitro at all of its C-C-G-G sites by using Hpa II methylase and was inserted into mouse Ltk- aprt- L cells by cotransformation, with the herpes virus thymidine kinase gene as a selectable vector. Whereas clones carrying unmethylated aprt sequences were found to have an aprt+ phenotype as shown by their ability to grow in azaserine-containing medium, almost all clones carrying methylated aprt sequences were shown to be phenotypically aprt-. Blot hybridization analysis demonstrated that both the methylated and unmethylated aprt sequences were integrated into the cellular genome to the same extent and that the in vitro modification was stably maintained in these cells for many generations. When clones containing methylated aprt genes were exposed to conditions that select for the expression of the aprt gene, a low frequency of reversion to the aprt+ phenotype was observed. In all of these clones, this reversion was accompanied by reorganization and undermethylation of the aprt sequences. These results show that the expression of certain genes may be inhibited by site-specific methylation of these sequences and suggest that methylation may play a direct role in the regulation of gene expression.
Heteropolymer filaments of vimentin and desmin in vascular smooth muscle tissue and cultured baby hamster kidney cells demonstrated by chemical crosslinking.
Authors: Quinlan R A , Franke W W
Published: May 2006

Certain smooth muscle cells of blood vessel walls as well as cultured baby hamster kidney cells contain simultaneously two different intermediate-sized filament (IF) proteins, desmin and vimentin. We have examined the question of the occurrence of both proteins in the same IF by chemically crosslinking the single cysteine group present in each of them. Oxidative crosslinking of filaments present in cytoskeletal preparations with cupric ion complexes of 1,10-phenanthroline resulted in formation of three types of dimers: vimentin-vimentin, desmin-desmin, and vimentin-desmin. These dimers were separated by NaDodSO4/polyacrylamide gel electrophoresis and characterized by binding of specific antibodies, by one- and two-dimensional gel electrophoresis of monomers obtained after cleavage of the disulfide bond by thiol agents, and by mapping of radioiodinated tryptic peptides. The demonstration of heterodimers of vimentin and desmin in vascular smooth muscle tissue of cow and chicken and in baby hamster kidney cells shows that the two proteins can be integrated in the same IF and can be nearest neighbors, oriented with their cysteine residues in a mirror-image symmetry. The possible existence of heteropolymer IF in other cell types is discussed.
Diverse forms of stress lead to new patterns of gene expression through a common and essential metabolic pathway.
Authors: Hammond G L , Lai Y K , Markert C L
Published: May 2006

Many eukaryotic organisms respond to heat shock by synthesizing new proteins. We examined the possibility that heat shock proteins represent a particular expression of a general response to stress and that, regardless of the nature of the effective stimulus, the same proteins are synthesized. Accordingly, cardiac stress was applied in the intact rat by four methods: banding the ascending aorta, increasing body temperature to 42 degrees C, reducing body temperature to 18 degrees C, and forcing the rat to swim until exhausted. The hearts were then extirpated and analyzed for new mRNA synthesis. The extracted RNA was translated in a cell-free medium containing [35S]methionine. Translation products were resolved by two-dimensional electrophoresis and visualized by autoradiography. Lactic acid concentration in heart tissue was determined enzymatically. The results showed that two new and distinct proteins of Mr 71,000 and isoelectric points of 5.8 and 6.1 were synthesized in hearts stressed by banding and by heating but not in hearts of exhausted swimmers or in animals at reduced body temperatures. There was no significant difference in cardiac lactic acid concentration between control hearts and hearts from swimmers or cold-treated animals. However, there was a 2-fold increase in lactic acid concentration in hearts of rats with banded aortas compared to controls and a 10-fold increase in heat shocked hearts. We conclude that, under conditions in which the energy requirements of the heart are not completely met by aerobic processes, the resultant lactic acidosis creates an intracellular environment that leads to the selective activation of genes, the production of new mRNA, and the synthesis of a typical group of stress proteins.
Construction of a yeast actin gene intron deletion mutant that is defective in splicing and leads to the accumulation of precursor RNA in transformed yeast cells.
Authors: Gallwitz D
Published: May 2006

The actin gene in yeast Saccharomyces cerevisiae is interrupted by a 309-base-pair intron within the protein-coding region. By using nuclease BAL-31, several intron deletion mutants were constructed to define sequences at the 5' splice junction that are required for RNA splicing. Extensive parts of the intron can be removed without affecting correct splicing. One mutant gene from which the invariant thymidine residue in the second intron position was deleted led to the accumulation of large amounts of unspliced actin mRNA when introduced into yeast cells through a recombinant high-copy-number plasmid. No evidence for the usage of alternative splice sites was obtained.
Intracellular potassium: 40K as a primordial gene irradiator.
Authors: Moore F D , Sastry K S
Published: May 2006

We have been interested in the possibility that the low energy electrons (Auger and Coster-Kronig) emitted after the electron capture decay of 40K may have highly localized radiochemical effects on the genetic material--effects dependent upon the intracellular locus of potassium. We report here that these effects are such that the likelihood of mutagenesis by their impact on DNA is substantial. This suggests that intracellular 40K has played a significant role as a mutagenic agent in evolution.
Antigen presentation by Ia+ B cell hybridomas to H-2-restricted T cell hybridomas.
Authors: Kappler J , White J , Wegmann D , Mustain E , Marrack P
Published: May 2006

The Ia+, H-2d BALB/c lymphoma cell line L10.A 2J was fused to T cell-depleted spleen cells from mouse strains bearing other H-2 haplotypes. A portion of the selected hybrids expressed Ia antigens of the normal spleen cell partner in the fusion as evidenced by their presentation of various antigens to a set of antigen-specific I-region-restricted T cell hybridomas. Three cloned hybrids were studied in detail. Antigen presentation was shown to be inhibited specifically by monoclonal anti-Ia antibodies. Both I-A and I-E molecules were expressed, including in the one case examined hybrid I-A and I-E molecules between the H-2d and H-2b haplotypes. These Ia+ B cell hybridomas provide a useful set of tools for studying the role of I-region-encoded molecules in antigen presentation to T cells.
Long-term culture of B lymphocytes and their precursors from murine bone marrow.
Authors: Whitlock C A , Witte O N
Published: May 2006

Growth of mature B cells and their precursors from mouse bone marrow was maintained in culture for greater than 1 year. Feeder layers of adherent bone marrow cells, established in medium containing fetal calf serum and no exogenous steroids, were used to provide an in vitro environment that supported continuous growth and development of these cells. In such bone marrow cultures, the number of cells bearing membrane immunoglobulin increased gradually for 4 wk and then decreased. Between 10 and 14 wk, some of the cultures gave rise to continuously dividing B-cell populations that contained pre-B cells (producing mu heavy chains only and sensitive to transformation by Abelson murine leukemia virus) as well as mature B cells (synthesizing both light and heavy chains of IgM). Immunoglobulin molecules synthesized by cells in these populations were heterogeneous in two-dimensional gel analysis. This suggests that mature B cells arose via maturation of pre-B cells in the cultures that involved rearrangement and expression of different variable region gene segments.
Evidence in support of a self-perpetuating HLA-DR-dependent delayed-type cell reaction in rheumatoid arthritis.
Authors: Klareskog L , Forsum U , Scheynius A , Kabelitz D , Wigzell H
Published: May 2006

Originating from observations on similarities between the rheumatoid synovial tissue and skin lesions in delayed-type hypersensitivity reactions--similarities as to massive infiltrates of "helper" T lymphocytes close to HLA-DR-expressing macrophage/dendritic cells--a notion is formed on the importance of local macrophage-dependent helper T-cell activation in the rheumatoid joint similar to that in a delayed-type skin reaction. In vitro studies on suspended synovial cells have been used to test and qualify these ideas. It is shown that (i) HLA-DR-expressing cells in normal synovial intima can, like epidermal Langerhans cells, mediate T-cell activation; (ii) the large numbers of rheumatoid synovial HLA-DR-expressing macrophage-like/dendritic cells are heterogeneous and mediate either efficient activation or suppression of T-lymphocyte proliferation, and (iii) specificity of rheumatoid T cells can be analyzed with the help of autologous synovial antigen-presenting cells; a specific anti-collagen type II response is reported in three patients.
Three Drosophila mutations that block associative learning also affect habituation and sensitization.
Authors: Duerr J S , Quinn W G
Published: May 2006

Drosophila melanogaster has been cultured with shock to avoid various odors. Mutants that failed to learn this task have been isolated. Here we report tests on these mutants for more elementary types of behavioral plasticity--habituation and sensitization of a reflex. Fruit flies have taste receptors on their feet. When a starved, water-satiated fly has sucrose applied to one foot, it usually responds by extending its proboscis. In normal flies this feeding reflex shows habituation: application of sugar to one foot depresses responsiveness through the contralateral leg for at least 10 min. The reflex also shows brief sensitization application of concentrated sucrose solution to the proboscis increases subsequent responsiveness to tarsal stimulation for 2-5 min. In three associative learning mutants , the proboscis-extension reflex is present with a normal threshold but behavioral modulation of the response is altered. The dunce, turnip, and rutabaga mutants all habituate less than normal flies. In addition, sensitization wanes unusually rapidly in dunce and rutabaga flies, lasting less than a minute in the case of dunce.
Specificity and localization of the acetylcholine receptor kinase.
Authors: Davis C G , Gordon A S , Diamond I
Published: May 2006

Acetylcholine receptor-phosphorylation has been compared in sealed and lysed right-side-out membrane vesicles prepared form Torpedo californica electric organ. Phosphorylation was increased 5- to 12-fold in hypotonically lysed vesicles as compared with untreated vesicles. Control experiments confirm that this enhancement is a result of increased permeability of the membrane to ATP. These data suggest that the acetylcholine receptor kinase is located on the cytoplasmic side of the plasma membrane. Results with detergent lysis support this conclusion. Although the acetylcholine receptor constitutes less than 10% of the total protein in these membranes, the kinase was found to be highly specific for polypeptides corresponding in molecular weight to acetylcholine receptor subunits.
Acute leukemia viruses E26 and avian myeloblastosis virus have related transformation-specific RNA sequences but different genetic structures, gene products, and oncogenic properties
Authors: Bister Klaus , Nunn Michael , Moscovici Carlo , Perbal Bernard , Baluda Marcel A. , Duesberg Peter H.
Published: May 2006

Replication-defective acute leukemia viruses E26 and myeloblastosis virus (AMV) cause distinct leukemias although they belong to the same subgroup of oncogenic avian tumor viruses based on shared transformation-specific (
onc
) RNA sequences. E26 causes predominantly erythroblastosis in chicken and in quail, whereas AMV induces a myeloid leukemia. However, upon cultivation
in vitro
for >1 month, a majority of surviving hemopoietic cells of E26-infected animals bear myeloid markers similar to those of AMV-transformed cells. We have analyzed the genetic structure and gene products of E26 virus for a comparison with those of AMV. An E26/helper virus complex was found to contain two RNA species: a 5.7-kilobase (kb) RNA that hybridizes with cloned AMV-specific proviral DNA and hence is probably the E26 genome; and an 8.5-kb RNA that is unrelated to AMV and represents helper virus RNA. Thus, E26 RNA is smaller than 7.5-kb AMV RNA. Hybridization of size-selected poly(A)-terminating E26 RNA fragments with AMV-specific DNA indicated that the shared specific sequences are located in the 5′ half of the E26 genome as opposed to a 3′ location in AMV RNA. In nonproducer cells transformed
in vitro
by E26, a
gag
-related nonstructural 135,000-dalton protein (p135) was found. No
gag
(Pr76) or
gag-pol
(Pr180) precursors of essential virion proteins, which are present in AMV nonproducer cells, were observed. p135 was also found in cultured E26 virus producing cells of several leukemic chickens, and its intracellular concentration relative to that of the essential virion proteins encoded by the helper virus correlates with the ratio of E26 to helper RNA in virions released by these cells. p135 is phosphorylated but not glycosylated; antigenically it is not related to the
pol
or
env
gene products. It appears to be coded for by a partial
gag
gene and by E26-specific RNA sequences, presumably including those shared with AMV. Hence, AMV and E26 appear to use different strategies for the expression of related
onc
sequences: AMV is thought to encode a transforming protein via a subgenomic mRNA, whereas E26 codes for a
gag
-related polyprotein via genomic RNA. It is speculated that differences in the oncogenic properties of E26 and AMV are due to differences in their genetic structures and gene products.
Alteration in phospholipid methylation and impairment of signal transmission in persistently paramyxovirus-infected C6 rat glioma cells.
Authors: Münzel P , Koschel K
Published: May 2006

The paramyxoviruses measles (subacute sclerosing panencephalitis, SSPE) virus and canine distemper virus (CDV) cause an impairment of the catecholamine-induced beta-adrenergic receptor-dependent cAMP generation in persistently infected C6 rat glioma cells. In C6 cells persistently infected with CDV the number of receptors is greatly reduced. Hirata and Axelrod have shown that the number of beta-adrenergic receptors could be regulated by methylation of phosphatidylethanolamine, resulting in lecithin synthesis [Hirata, F. & Axelrod, J. (1980) Science 209, 1082-1090]. We have therefore studied the methylation of phosphatidylethanolamine in persistently infected cells by the incorporation of [3H]methyl groups from [methyl-3H]methionine into phosphatidylethanolamine. In both infected systems, C6/ SSPE and C6/CDV, we observed a total loss of catecholamine-stimulated beta-adrenergic receptor-dependent methylation, whereas the beta-receptor-independent methylation of phospholipids was unchanged.
Covalent crosslinking of angiotensin II to its binding sites in rat adrenal membranes.
Authors: Paglin S , Jamieson J D
Published: May 2006

To identify the molecular components of the angiotensin II (AII) receptor in the adrenal cortex, we have covalently linked 125I-labeled AII (125I-AII) to its binding sites by using the chemical crosslinker disuccinimidyl suberate. Membrane fractions from rat adrenal tissue were incubated with 125I-AII, washed, and treated with disuccinimidyl suberate. NaDodSO4/polyacrylamide gel electrophoresis carried out under reducing conditions followed by autoradiography showed that a major polypeptide(s) with an average Mr of 116,000 was covalently tagged with 125I-AII. Proteins with Mr of 54,000 and 45,000 were also lightly labeled. Labeling of the Mr 116,000 species was specific in that it could be abolished by prior incubation of the membranes with [Sar1,Leu8]AII or unlabeled AII. Labeling of the smaller proteins was less affected by prior incubation with [Sar1,Leu8]AII. Experiments in which crosslinking was carried out in the presence of a variety of protease inhibitors indicated that the Mr 116,000 species is not an enzyme involved in AII degradation. Gel electrophoresis under nonreducing conditions showed that this component is not derived from larger disulfide-linked entities. We suggest that the Mr 116,000 moiety is a part of the receptor system for AII. The relationship, if any, of the Mr 54,000 and 45,000 peptides to the AII receptor remains unknown.
Overlapping evolutionary affinities revealed by comparison of amino acid compositions.
Authors: Yeh W K , Shih C , Ornston L N
Published: May 2006

Comparison of the amino acid compositions of purified proteins indicates the presence of overlapping evolutionary affinities among enzymes of the beta-ketoadipate pathway. Isofunctional enzymes from different bacterial genera share a common evolutionary origin. Moreover, enzymes that mediate isofunctional or chemically analogous reactions within an organism appear to be evolutionarily homologous. Most remarkably, closely similar amino acid compositions are found in enzymes that mediate the following consecutive metabolic steps: lactonization, decarboxylation, hydrolysis, and transfer of a thioester bond.
Cholesterol synthesis in polyclonally activated cytotoxic lymphocytes and its requirement for differentiation and proliferation.
Authors: Heiniger H J , Marshall J D
Published: May 2006

The kinetics of sterol synthesis and DNA synthesis in polyclonally activated, concanavalin A-stimulated spleen cell cultures were analyzed. Inhibition of DNA synthesis by 1-beta-D-arabinofuranosylcytosine (Ara-C) did not abrogate the formation of cytotoxic effector cells. However, inhibition of sterol synthesis by 25-hydroxycholesterol inhibited formation of cytotoxic effector cells as well as cellular proliferation. The inhibition of cytotoxicity correlated well with the dose of 25-hydroxycholesterol administered and was dependent on the time of administration. The agent had to be present when sterol synthesis occurred normally during the time lapse before DNA synthesis began. Compactin had the same effect as 25-hydroxycholesterol. The effects of inhibition of sterol biosynthesis on cytotoxicity could be counteracted by addition of cholesterol-containing liposomes. Based on these experiments, the links between proliferation and differentiation in lymphocytes are discussed.
Selective blockade of human natural killer cells by a monoclonal antibody.
Authors: Newman W
Published: May 2006

A murine monoclonal antibody, 13.1, which blocks human natural killer (NK) cell-mediated lysis, has been developed. Hybridoma 13.1 was derived by fusion of NS-1 cells with spleen cells from mice immunized with an enriched population of NK cells. Supernatants of growing hybridomas were screened for their ability to block NK cell-mediated lysis of K562 targets. Antibody 13.1 is an IgG1 with a single light chain type and it does not fix complement. The 13.1 antigen is expressed on all peripheral blood mononuclear cells, with an antigen density approximately 1/30th that of HLA antigen heavy chain. Pretreatment and washing experiments revealed that inhibition of cytotoxicity occurred at the effector cell level only. Significant blocking was achieved with nanogram quantities of antibody and was not due to toxic effects on NK cells. Likewise, controls with other antibodies of the same subclass demonstrated that blocking was not a consequence of mere binding to NK cells. When a panel of 17 NK cell-susceptible targets was tested, the lysis of only 5 of these was blocked, namely K562, HL-60, KG-1, Daudi, and HEL, a human erythroleukemic cell line. The lysis of 12 human B cell and T cell line targets was not inhibited. In addition to the demonstration that the 13.1 antigen is a crucial cell surface structure involved in NK lysis, a heterogeneity of target cell recognition has been revealed that argues for the proposition that individual NK cells have multiple recognitive capabilities.
Viruses of symbiotic
Chlorella
-like algae isolated from
Paramecium bursaria
and
Hydra viridis
Authors: Van Etten James L. , Meints Russel H. , Kuczmarski Daniel , Burbank Dwight E. , Lee Kit
Published: May 2006

We previously reported that isolation of symbiotic
Chlorella
-like algae from the Florida strain of
Hydra viridis
induced replication of a virus (designated HVCV-1) in the algae. We now report that isolation of symbiotic
Chlorella
-like algae from four other sources of green hydra and one source of the protozoan
Paramecium bursaria
also induced virus synthesis. Algae from one of these hydra contained a virus identical to HVCV-1 (based on its rate of sedimentation, buoyant density, reaction to HVCV-1 antiserum, and DNA restriction fragments) whereas algae from the other three hydra contained another similar, but distinct, virus (designated HVCV-2). The virus from the paramecium algae (designated PBCV-1) was distinct from both HVCV-1 and HVCV-2. The symbiotic algae in the hydra could also be distinguished ultrastructurally. Chloroplasts of both algae that produced HVCV-1 lacked a pyrenoid whereas chloroplasts of the other three symbiotic algae contained pyrenoids. Since all symbiotic eukaryotic algae we have examined have had virus, a potential viral role in symbiosis is suggested.
Enkephalin convertase: purification and characterization of a specific enkephalin-synthesizing carboxypeptidase localized to adrenal chromaffin granules.
Authors: Fricker L D , Snyder S H
Published: May 2006

A specific carboxypeptidase that converts enkephalin precursors into enkephalin in adrenal chromaffin granules has been purified and characterized. In the adrenal this enzyme, designated enkephalin convertase, is uniquely localized to the chromaffin granules, which contain enkephalin and precursor peptides. Enkephalin convertase is markedly stimulated by CoCl2 and inhibited by EDTA or 1,10-phenanthroline, unlike the lysosomal carboxypeptidase. The purified enzyme has a high affinity for the hexapeptides [Met5]- and [Leu5]enkephalin-Arg6 (51 and 83 microM, respectively) and a somewhat lower affinity for the hexapeptides [Met5]- and [Leu5]enkephalin-Lys6 (195 and 174 microM). Brain enkephalin convertase shows 10-fold regional variations, unlike other carboxypeptidases, which are uniformly distributed. Enkephalin convertase appears to be associated selectively and physiologically with biosynthesis of the enkephalins.
Statistical hydromechanics of the solar differential rotation
Authors: Monin Andrei S. , Simuni Lazar M.
Published: May 2006

An axisymmetric hydrodynamic model of the solar differential rotation is suggested that differs from the previous axisymmetric models (with arbitrarily given anisotropic viscosity) in the use of the hydrodynamic equations (the Friedmann-Keller equations) for the statistical second moments of the fluctuations of velocity and entropy—i.e., turbulent fluxes of momentum and entropy. The model gives a correct reproduction of the differential rotation (without unreal temperature differences on the Sun's surface peculiear to the anisotropic viscosity models) and makes possible calculations of the second moments.
Spatial homogeneity and redshift-distance laws
Authors: Nicoll J. F. , Segal I. E.
Published: May 2006

Spatial homogeneity in the radial direction of low-redshift galaxies is subjected to Kafka-Schmidt V/V

m

tests using well-documented samples. Homogeneity is consistent with the assumption of the Lundmark (quadratic redshift-distance) law, but large deviations from homogeneity are implied by the assumption of the Hubble (linear redshift-distance) law. These deviations are similar to what would be expected on the basis of the Lundmark law. Luminosity functions are obtained for each law by a nonparametric statistically optimal method that removes the observational cutoff bias in complete samples. Although the Hubble law correlation of absolute magnitude with redshift is reduced considerably by elimination of the bias, computer simulations show that its bias-free value is nevertheless at a satistically quite significant level, indicating the self-inconsistency of the law. The corresponding Lundmark law correlations are quite satisfactory satistically. The regression of redshift on magnitude also involves radial spatial homogeneity and, according to R. Soneira, has slope determining the redshift-magnitude exponent independently of the luminosity function. We have, however, rigorously proved the material dependence of the regression on this function and here exemplify our treatment by using the bias-free functions indicated, with results consistent with the foregoing argument.
Ab initio
calculations of dilithiopropenes
Authors: Kost Daniel , Klein Joseph , Streitwieser Andrew , Schriver George W.
Published: May 2006

Ab initio
molecular orbital calculations with the 3-21G basis set show the most stable dilithiopropene structure to be the di-π lithium-bridged structure VI of 1,3-dilithiopropene. This structure is most simply regarded as an ion triplet of two lithium cations and a propenylidene dianion.
Examples of constant mean curvature immersions of the 3-sphere into euclidean 4-space
Authors: Hsiang Wu-yi , Teng Zhen-huan , Yu Wen-ci
Published: May 2006

Mean curvature is one of the simplest and most basic of local differential geometric invariants. Therefore,
closed hypersurfaces
of constant mean curvature in euclidean spaces of high dimension are basic objects of fundamental importance in global differential geometry. Before the examples of this paper, the only known example was the obvious one of the round sphere. Indeed, the theorems of H. Hopf (for immersion of
S
2
into
E
3
) and A. D. Alexandrov (for imbedded hypersurfaces of

E
n

) have gone a long way toward characterizing the round sphere as the only example of a closed hypersurface of constant mean curvature with some added assumptions. Examples of this paper seem surprising and are constructed in the framework of equivariant differential geometry.
Nonoxidative ethanol metabolism: formation of fatty acid ethyl esters by cholesterol esterase.
Authors: Lange L G
Published: May 2006

The recent identification of myocardial metabolites of ethanol--fatty acid ethyl esters--suggests that some of the pathophysiological derangements associated with alcohol-induced heart muscle disease may be a consequence of products of myocardial ethanol metabolism. The donor of the fatty acid moiety in the formation of fatty acid ethyl esters has been identified as nonesterified fatty acid. Fatty acid esterification with ethanol is shown to be mediated by cholesterol esterase (sterol-ester acylhydrolase, EC 3.1.1.13), a finding that identifies a singular nonoxidative ethanol metabolism by an enzyme. A potential basis for the protective effect of ethanol ingestion on atherogenesis is also suggested because fatty acid ethyl esters inhibit cholesterol esterification catalyzed by pancreatic cholesterol esterase and hepatic and aortic microsomal fatty acyl-CoA:cholesterol O-acyltransferase (EC 2.3.1.26).
Pyrophosphate inhibition of rho ATPase: a mechanism of coupling to RNA polymerase activity.
Authors: Kent R B , Guterman S K
Published: May 2006

The effects of pyrophosphate on RNA binding and ATPase activities of Escherichia coli transcription termination factor rho have been studied. Mutant rho-115 protein has a temperature-sensitive RNA-dependent ATPase activity due to the thermolability of binding to RNA [Kent, R.B. & Guterman, S.K. (1981) Fed. Proc. Fed. Am. Soc. Exp. Biol. 40, 1765 (abstr.)]. The presence of either ATP or pyrophosphate at comparable concentrations stabilizes the binary complex of rho and poly(C) at high temperature. ADP at 8-fold greater concentration also stabilizes the mutant rho-RNA binary complex. Pyrophosphate is a noncompetitive inhibitor (Ki = 0.07 mM) of rho poly(C)-dependent ATPase, an activity that is required for rho-mediated termination. These results suggest the existence of a regulatory site on the rho molecule. We suggest that rho NTPase is regulated by RNA polymerase (EC 2.7.7.6) so that during transcription elongation the RNA polymerase competes successfully with rho for substrates and inhibits rho NTPase with product pyrophosphate. Further, RNA polymerase pausing may result in reduced pyrophosphate and increased NTP concentrations, allowing rho NTPase to function.
Joining of immunoglobulin heavy chain gene segments: implications from a chromosome with evidence of three D-JH fusions.
Authors: Alt F W , Baltimore D
Published: May 2006

A chromosomal segment with a unique structure around the immunoglobulin heavy chain joining region (JH) has been molecularly cloned from an Abelson murine leukemia virus-transformed cell line. Attached to JH3 in the cloned DNA, in inverted sequence, is the DNA from JH1 to the JH2 recognition sequence. The inverted segment is attached at its other end to the 5' recognition sequence of a diversity segment (D). To form this structure, three joining events must have occurred on the same chromosome. One of these events could have been a normal D-JH joining but the others must have been irregular events including ones that result in inversions. One of the joining events left fused recognition elements from JH2 and a D whose sequence shows that, during joining, reciprocal joinings of the recognition elements must occur to fuse the heptameric elements back to back. Because joined D and JH undergo deletion of terminal coding sequence during recombination but the joined heptameric recognition sequences do not contain the deleted sequence, joining must be a nonreciprocal event. Also, extra nucleotides are inserted between D and JH as part of the joining process; it is suggested that this added sequence is a product of the activity of terminal deoxynucleotidyltransferase at the D/JH (and probably the VH/D) joints and that it represents a new element of heavy chain gene structure, the N region.
Mutational specificity of UV light in Escherichia coli: indications for a role of DNA secondary structure.
Authors: Todd P A , Glickman B W
Published: May 2006

We used the lacI forward mutagenesis system to determine the mutational specificity of UV-induced mutation in a repair-proficient (Uvr+) and a repair-deficient (delta UvrB) strain of Escherichia coli. The spectra recovered at similar levels of mutagenesis were similar, the exception being a mutational hotspot at site A24 specific to the delta UvrB strain. Mutations induced at this hotspot, as well as those induced at other mutational hotspots that were found to be common to both the Uvr+ and Uvr- strains, involve G . C leads to A . T transitions. All of the hotspots are at sites of potential dipyrimidine photoproducts, such as thymine-cytosine and cytosine-cytosine dimers, or of pyrimidine-cytosine photoproduct Py-C lesions. Each of these hotspots occurs at a site in the potential hairpin loop of quasi-palindromic sequences. These observations suggest an important role for DNA structure in determining the fate of UV-induced premutational lesions.
T-cell proliferative response to hapten-modified self-immunoglobulins: recognition of conjugate-specific determinants.
Authors: Bikoff E
Published: May 2006

(4-Hydroxy-3-nitrophenyl)acetyl (NP)-modified BALB/c immunoglobulins were used as the immunogen for induction of a proliferative response in BALB/c mice. As is true for responses to other soluble antigens, proliferation was dependent on Lyt-1 cells and histocompatible radioresistant accessory cells. Lyt-1 cells directed against NP-modified self immunoglobulin are specific for the immunizing hapten NP. However, they do not recognize hapten per se. Rather, they see complex determinants comprised of both the hapten NP and the immunoglobulin self-carrier. Distinct specificities were created by coupling the same hapten to different monoclonal BALB/c antibody molecules or by attaching the hapten to the immunoglobulin self-carrier via a spacer molecule. It is proposed that determinants created by attaching haptens to self-immunoglobulin molecules are similar to those recognized by anti-idiotypic T cells.
Conservative integration of bacteriophage Mu DNA into pBR322 plasmid.
Authors: Liebart J C , Ghelardini P , Paolozzi L
Published: May 2006

In order to clarify the first step in Mu integrative recombination, we have infected a bacterial strain harboring the plasmid pBR322 and isolated Mu DNA in a supercoiled form associated with this plasmid. These structures show an association of Mu with PBR322 without any preliminary replication.
Production of viable adult trisomy 17 reversible diploid mouse chimeras.
Authors: Epstein C J , Smith S A , Zamora T , Sawicki J A , Magnuson T R , Cox D R
Published: May 2006

Aneuploid mouse embryos and fetuses are an important system for investigating the pathogenesis of the developmental and functional consequences of chromosome imbalance in mammals. However, the fact that almost all mouse aneuploids die in embryonic or fetal life restricts their usefulness for studies of loci and functions that are expressed only after birth. As an approach to rescuing aneuploid cells, we have prepared chimeras by aggregating aneuploid embryos with diploid embryos at the 8-16 cell stage. This technique has allowed us to produce trisomy 17 reversible diploid (Ts17 reversible 2n) chimeras containing cells of a trisomic state, which is ordinarily lethal at 10-12 days of gestation. All of the analyzed organs from the chimeras, including brain, liver, kidney, lung, muscle, heart, thymus, spleen, bone marrow, blood, and skin, contained both Ts17 and 2n cells. The proportion of Ts17 cells in each organ as estimated from coat color, enzyme markers (glucosephosphate isomerase), and karyotypes ranged from 5% to 85%, most commonly 20-40%. This is in contrast to the control 2n reversible 2n chimeras in which the 2n component on the same genetic background as the Ts17 generally comprised 60-90% of the cell population. The growth rates of the living Ts17 reversible 2n chimeras were in the lower half of the normal range, and the oldest animals are now age 14 mo. No progeny were obtained from Ts17 germ cells in the two fertile T217 reversible 2n chimeras. In comparison with analogous human situations, it is striking that, except for a kink in the tail of one living animal, none of the Ts17 reversible 2n chimeras had any discernible structural abnormalities. Our findings indicate that it is feasible to rescue cells from autosomal aneuploidies that otherwise result in early fetal death.
Serological analysis of cell surface antigens of null cell acute lymphocytic leukemia by mouse monoclonal antibodies.
Authors: Ueda R , Tanimoto M , Takahashi T , Ogata S , Nishida K , Namikawa R , Nishizuka Y , Ota K
Published: May 2006

Nine antigens systems were defined. Two were related to HLA-A,B,C and to Ia-like antigens; the others could be grouped into three categories. (i) NL-22, NL-1: NL-22 antibody reacted with leukemia cells from 12 to 16 cases of null cell acute lymphocytic leukemia (null-ALL) but not with any other type of leukemia tested or with lymphoid cells of various origins. Among cultured cell lines tested, one (NALM-6) of three null-ALL cell lines was positive, the others were negative. Absorption analysis confirmed the restriction of NL-22 antigen to null-ALL. NL-1 antibody was reactive with leukemia cells from 10 to 16 cases of null-ALL and 3 of 6 cases of chronic myelocytic leukemia in blastic crisis (CML-BC). The antigen was present also on a minor population of normal lymphoid cells. The distribution and molecular weight (100,000; glycoprotein) of the NL-1 antigen resembled that of the previously described common ALL antigen (cALL). (ii) NL-30, NL-4: Both antibodies exhibited almost identical patterns of reactivities against cultured cell lines tested. They reacted with leukemia cells from some cases of null-ALL, adult T-cell leukemia, and CML-BC, although they showed discordance in their reactivities against a panel of leukemia cells, (iii) NL-9, NL-8, NL-25: These three antibodies detect serologically distinguishable determinants on a broad range of leukemias and normal lymphoid and hematopoietic cell types. The antibodies analyzed in this study provide evidence for the heterogeneity of null-ALL by demonstrating a variety of antigen phenotypes on leukemia cells. One of the antigens (NL-22) appears to be restricted to null-ALL.
Polyploid megakaryocytes develop randomly from a multicompartmental system of committed progenitors.
Authors: Paulus J M , Prenant M , Deschamps J F , Henry-Amar M
Published: May 2006

Cumulative distributions of the number of doublings undergone by mixed megakaryocytic/erythroblastic colonies and by pure megakaryocytic colonies were determined from plasma clot cultures of bone marrow (from C57BL/6 mice) supplemented with erythropoietin. Analysis of these distributions suggests that these colonies are produced by three distinct progenitors. At days 7-14, progenitors of mixed megakaryocytic/erythroblastic colonies (BFU-ME) generate tri-exponential distributions and the mean (+/- SD) fraction of this progenitor pool ceasing to proliferate per doubling (FCP) increases stepwise from 0.07 +/- 0.06 to 0.27 +/- 0.07 and 0.73 +/- 0.07. In this interval, progenitors of pure megakaryocytic colonies (CFU-M) generate bi-exponential slopes whose FCP values are compatible with the two last slopes above. Finally, CFU-M at day 3 express only the last slope. From days 5 to 9, megakaryocytes generated by BFU-ME reach lower ploidy levels than do those generated by CFU-M. It is concluded that, in the culture system used, (i) megakaryocyte progenitors that do not switch to polyploidization mature through the three consecutive compartments indicated, (ii) each progenitor population has a probability of becoming polyploid that reflects the fraction that ceases to proliferate, (iii) the exponentially distributed mitotic reserve of progenitors is determined by the combination of maturing into the next compartment and the probabilistic switch to the pathway of polyploidization, and (iv) the ploidy distribution of megakaryocytes probably depends on the progenitor from which they originate.
5-Azacytidine stimulates fetal hemoglobin synthesis in anemic baboons.
Authors: DeSimone J , Heller P , Hall L , Zwiers D
Published: May 2006

In an attempt to stimulate Hb F synthesis in baboons by means other than erythropoietic stress, we considered the possibility that an agent that inhibits methylation of CpG sequences in DNA may be effective. 5-Azacytidine, a cytosine analogue that cannot be methylated, is such an agent. Animals whose packed red cell volume was maintained at approximately 20% by bleeding were given 10 daily intravenous injections of the drug (6 mg/kg) in 12 days. Hb F levels in these animals started to increase on day 5 of this regimen and peak levels, which were 6-30 times higher than those produced by bleeding alone, occurred 5-7 days after the last dose of the drug. In animals previously identified as genetically "high" or "low" Hb F responders, the maximal Hb F levels were 70-85% and 35-40% respectively. In dose-response studies 5-azacytidine given daily at 3-4 mg/kg produced maximal Hb F increases. The drug did not correlate the percentage (number) of Hb F-containing cells (F cells) beyond the maximal number achieved by bleeding alone and thus its main effect was to increase Hb F per F cell. The finding that Hb F synthesis can be modulated to such a high degree by a drug may have therapeutic implications--e.g., in sickle cell anemia, in which stimulation of Hb F synthesis may prevent sickling.
Cystine accumulation and loss in normal, heterozygous, and cystinotic fibroblasts.
Authors: Jonas A J , Greene A A , Smith M L , Schneider J A
Published: May 2006

Cystinotic fibroblasts contain approximately 100 times more cystine than do normal control fibroblasts. When cystinotic fibroblasts were placed in the presence of 30 mM cysteine-glutathione mixed disulfide (CSSG) for 24 hr, their cystine content increased about 3-fold. Similar treatment of normal fibroblasts and fibroblasts from patients heterozygous for cystinosis resulted in a 6- to 7-fold increase in cystine content. In all three cell types, the intracellular free cystine is located within lysosomes. When placed in cystine-free medium after 24 hr in CSSG-containing medium, the normal and heterozygous fibroblasts rapidly lost their lysosomal cystine (t 1/2 = 20 min), but the cystine content of the cystinotic cells remained stable for over 90 min. In contrast to the findings in intact fibroblasts, cystine loss could not be demonstrated from isolated, cystine-loaded lysosomes from any of the three cell types.
Localization of peptide YY (PYY) in gastrointestinal endocrine cells and effects on intestinal blood flow and motility.
Authors: Lundberg J M , Tatemoto K , Terenius L , Hellström P M , Mutt V , Hökfelt T , Hamberger B
Published: May 2006

In immunohistochemical studies using antisera to peptide YY (PYY), a 36 amino acid polypeptide isolated from porcine duodenum, it was found that PYY-like immunoreactivity occurred mainly in endocrine cells of the gastrointestinal mucosa. PYY-immunoreactive cells were particularly abundant in the distal intestine and have been observed in five species, including man. By radioimmunoassay it was found that, in the rat, the amount of PYY immunoreactivity was about 100-fold higher in the colon than in the duodenum. The chromatographic profiles of PYY immunoreactivity from the rat colon and porcine PYY on a SP-Sephadex ion exchanger were similar. Furthermore, serial dilutions of extracts from the rat colon and porcine PYY had parallel displacement curves in radioimmunoassay. Close intraarterial administration of PYY in cats caused an intestinal vasoconstriction and an inhibition of jejunal and colonic motility. Simultaneously there was a rise in systemic arterial blood pressure. These effects of PYY were also observed after pretreatment with adrenergic blocking agents. It is concluded that PYY is a gastrointestinal peptide that is present mainly in endocrine cells of distal intestine and that has effect on both intestinal motility and the cardiovascular system.