bluuebunny/crossref_metadata_2025 huggingface dataset:
Potent stimulation of vascular endothelial cell growth by differentiated 3T3 adipocytes.
Authors: Castellot J J , Karnovsky M J , Spiegelman B M
Published: May 2006

3T3 cells that have undergone adipose differentiation in vitro secrete into the culture medium a potent growth stimulatory activity for bovine aortic endothelial cells. When medium containing 2% fetal calf serum, which does not support significant endothelial cell growth, is conditioned by 3T3-F442A adipocytes, the endothelial cells grow rapidly (doubling time, 24 hr) at a rate equal to the growth rate in 20% fetal calf serum. The potency of the conditioned medium is further shown by the fact that it can be diluted 1:5 with little apparent loss of activity and shows a half-maximal stimulation at 10 microliter/ml. Serum is not required for either the secretion of this mitogen by the adipocytes or its action on the endothelial cells, as shown by the fact that the latter are stimulated to divide in serum-free medium conditioned by the adipocytes. The growth stimulatory activity appears to be specific for vascular endothelial cells in that no other cell type examined, including vascular smooth muscle cells and pericytes, are significantly stimulated by medium conditioned by 3T3-F442A cells. Similarly, medium conditioned by no other cell type examined has more than 10% of the activity of medium conditioned by the adipocytes. The specificity and potency of the adipocyte-derived factor suggest that it may play a role in the vascularization of this tissue during development. Preliminary biochemical analysis indicates that the adipocyte factor is nondialyzable and is not inactivated by heat or proteases. The protease insensitivity distinguishes the adipocyte growth stimulatory activity from the low levels of activity secreted by fibroblasts and preadipocytes, suggesting that the adipocyte mitogen is a product specifically related to the differentiation process.
Molecular cloning of a human histocompatibility antigen cDNA fragment.
Authors: Ploegh H L , Orr H T , Strominger J L
Published: May 2006

A clone (pHLA-1) containing HLA-specific cDNA was constructed by reverse transcription of partially purified HLA mRNA from the human lymphoblastoid cell line LKT. The identity of pHLA-1 was established by its ability to hybridize to HLA heavy chain mRNA and by nucleotide sequence analysis. The pHLA-1 cDNA insert (approximately 525 base pairs) corresponds to the COOH-terminal 46 amino acids of an HLA-A, -B, or -C antigen (15 residues from the hydrophobic region and the remainder from the COOH-termial hydrophilic region), together with a portion of the 3' untranslated region of the mRNA.
Synthesis, intracellular distribution, and secretion of multiple forms of parathyroid secretory protein-I.
Authors: Morrissey J J , Shofstall R E , Hamilton J W , Cohn D V
Published: May 2006

Examination of whole cell extracts and subcellular fractions of dispersed porcine parathyroid cells incubated with [35S]methionine indicates that two species of secretory protein-I, 72,000 and 64,000 daltons, respectively, are synthesized. Two secretory protein-I species of molecular weights equivalent to those in the cell but with slightly different isoelectric points were secreted; calcium suppressed the secretion of both of these. The secretory protein-I of cell and medium were shown to be related to each other and to previously identified secreted secretory protein-I by comparison of their 35S-labeled tryptic peptides and location of methionine in positions 7, 15, and 32 of the peptide chains. Both of the cellular species appeared to be enclosed within membranes similar to those containing parathyroid hormone and its immediate biosynthetic precursor because they were associated with the membrane fraction of the cell, were not digested when the membranes were exposed to trypsin, and were extracted from these membranes, as were parathyroid hormone and proparathyroid hormone, with dilute sodium deoxycholate. We did not find an amino-terminal precursor form of secretory protein-I in an incubation as short as 2 min with [35S]methionine, whereas [35S]proparathyroid hormone was readily detected, indicating that processing of secretory protein-I involves a direct conversion of the pre-protein to the secretory protein-I. Posttranslational glycosylation or deletion of carboxy-terminal region of the secretory protein-I species might account for the differences in molecular weights and isoelectric points of the cellular and secreted forms.
Kinetic models suggest bimolecular reaction steps in axonal Na+-channel gating.
Authors: Dorogi P L , Neumann E
Published: May 2006

Abstract kinetic models that can successfully simulate the ion-permeability features of axonal Na+ channels suggest the presence of bimolecular reaction steps in the activation of the channels. A chemically plausible interpretation of minimum complexity is described. The implied chemical formalism is highly suggestive of an activator-controlled gating system with strong similarities to the acetylcholine-regulated system. Conformational changes that underlie the ion-conductance changes are suggested to possess a greater sensitivity to the membrane field in axonal parts of excitable membranes than at synaptic parts. This would allow axonal permeability changes to be energetically regulated more conservatively than is observed for synaptic ion channels. Axonal K+ channels with delayed activation kinetics would serve to reverse the increase in membrane permeability to Na+ with a minimum of chemical dissipation.
Initiation of DNA replication in a ColE1-type plasmid: isolation of mutations in the ori region.
Authors: Naito S , Uchida H
Published: May 2006

We have constructed a plaque-forming hybrid phage, lambda SN4, which behaves as a composite replicon of the lambda phage and a mini-ColE1 plasmid. From the hybrid phage, plaque-type mutants altered in the ability to replicate as a ColE1 replicon were isolated. These mutations were designated as cer, signifying ColE1 replication defective. One of such mutants, lambda SN4cer6, was studied further. The mutant DNA was unable to replicate in vivo if expression and function of its lambda replicon were inhibited. The defect could not be complemented in trans. DNA sequence determination of the mutant phage revealed a single base pair (bp) alteration, C-G to T-A, at 160 bp upstream from the ori site of its ColE1 replicon. From lambda SN4cer6, revertants were obtained that had regained function of the ColE1 replicon, and they could be classified into two groups that showed a full and a partial recovery in the rates of ColE1-driven DNA synthesis. DNA sequence determination of revertant DNA indicated that the former group contained true revertants, T-A to C-G, at the cer6 site, whereas one of the partial revertants was found to sustain a secondary-site mutation, G-C to A-T at 187 bp upstream of the ori site. It was possible to construct a hairpin structure that starts by hydrogen bonding of bases at the site -160 and -187.
A cardioactive factor in human plasma with positive inotropic and positive chronotropic activities
Authors: Kalman Sumner M. , Jones Ruth M.
Published: May 2006

A cardioactive factor with a molecular weight of about 100,000 and that exhibits positive inotropic and positive chronotropic activity on isolated guinea pig atria has been found in human plasma. The positive inotropic activity is less stable than the positive chronotropic activity. The two activities move together in cation- and anion-exchange chromatography, gelfiltration chromatography, and polyethylene glycol precipitation. They may be associated with a single large polypeptide or with different subunits of a complex protein.
Localization of anti-mitochondrial antibody in experimental canine myocardial infarcts.
Authors: Willerson J T , Kulkarni P , Stone M , Lewis S E , Eigenbrodt E , Bonte F J , Parkey R W , Buja L M
Published: May 2006

Alterations in cell and subcellular membrane integrity occur during evolving ischemic myocardial injury. We tested the hypothesis that an antibody against human liver mitochondria [anti-mitochondrial antibody developing in a patient with primary biliary cirrhosis] could identify altered cell membrane integrity in experimental canine myocardial infarcts. The proximal left anterior descending coronary arteries of 12 dogs were ligated and 1 hr later 131I-labeled F(ab')2 fragments from either a control human IgG (6 dogs) or anti-mitochondrial IgG (6 dogs) were injected. The 131I-labeled F(ab')2 anti-mitochondrial fragments concentrated maximally in the central infarct subendocardium [infarct-to-normal ratio of 9.2 +/- 3.5 (mean +/- SD) vs. 4.6 +/- 3.3 for control F(ab')2 IgG, P < 0.05]. There was also 1 1/2- to 2-fold greater anti-mitochondrial antibody F(ab')2 accumulation in the central infarct epicardium and the peripheral infarct subendocardium and subepicardium. Thus, an anti-mitochondrial antibody obtained from a patient with primary biliary cirrhosis concentrates in irreversibly damaged myocardium after experimental canine myocardial infarction. Presumably this occurs because of altered cell membrane integrity, which allows exposure of mitochondria to the anti-mitochondrial antibody. The F(ab')2 fragments of anti-mitochondrial antibodies labeled with suitable radionuclides should allow noninvasive scintigraphic detection of experimental acute myocardial infarcts.
Stationary convection in dilute solutions of
3
He in superfluid
4
He
Authors: Warkentin P. A. , Haucke H. J. , Lucas P. , Wheatley J. C.
Published: May 2006

Two symmetric, convecting steady states have been observed in a novel cell of unity aspect ratio and studied over a range of temperature for two concentrations of
3
He in superfluid
4
He. An existing theory due to Parshin has been related to the conditions necessary for convection in this system, defining a Rayleigh number closely analogous to that of a classical one-component Bénard system. Values of this Rayleigh number at the onset of convection calculated from experimental data are found to have little temperature dependence, with an average value near that for a classical one-component fluid in this geometry. The Prandtl number is small and temperature dependent, with a smallest calculated value of 0.05.
Novel RNA polymerase sigma factor from Bacillus subtilis.
Authors: Haldenwang W G , Losick R
Published: May 2006

A modified form of Bacillus subtilis RNA polymerase (RNA nucleotidyltransferase) has been isolated that exhibits distinctive transcriptional specificity. This modified enzyme transcribes two cloned genes from the purA-cysA region of the B. subtilis chromosome whose expression in vivo is associated with the process of sporulation. Neither of these genes is transcribed by the usual form of B. subtilis RNA polymerase holoenzyme containing a sigma factor of 55,000 daltons (sigma 55). The modified RNA polymerase lacks sigma 55 but contains a newly identified subunit of 37,000 daltons termed sigma 37. A reconstitution experiment in which sigma 37 was added to core RNA polymerase strongly suggests that sigma 37 is responsible for the transcriptional specificity of the modified RNA polymerase. Sigma 37 apparently acts at the level of promoter recognition; this transcriptional determinant enabled core RNA polymerase to form stable binary and ternary ("initiation") complexes with endonuclease restriction fragments containing promoters for the cloned B. subtilis genes.
Construction and identification of bacterial plasmids containing nucleotide sequence for human leukocyte interferon.
Authors: Maeda S , McCandliss R , Gross M , Sloma A , Familletti P C , Tabor J M , Evinger M , Levy W P , Pestka S
Published: May 2006

Bacterial plasmids containing human leukocyte interferon sequences were constructed and identified. Identification was confirmed by correspondence of the nucleotide sequence with out amino acid sequence of human leukocyte interferon. The finding of bacterial recombinants containing distinct leukocyte interferon sequences is consistent with our purification of different leukocyte interferon species. We conclude that what has been designated human leukocyte interferon is, indeed, a class of homologous proteins. Preliminary indications suggest that their diversity appears to be represented by individual genomic equivalents. Each of the individual species exhibits characteristic activities. The structural modulation of these biological activities has immense significance for understanding the natural role of the interferons and for refining and developing their ultimate therapeutic potential.
OK10, an avian acute leukemia virus of the MC29 subgroup with a unique genetic structure
Authors: Bister Klaus , Ramsay Gary , Hayman Michael J. , Duesberg Peter H.
Published: May 2006

The RNA of defective avian acute leukemia virus OK10 was isolated from a defective virus particle, released by OK10-transformed nonproducer avian fibroblasts, as a 60S complex consisting of 8.6-kilobase subunits. Oligonucleotide fingerprinting and RNA·cDNA hybridization identified two sets of sequences in OK10 RNA: group-specific sequences, which are related to all nondefective members of the avian tumor virus group, and a sequence closely related to the subgroup-specific sequences (
mcv
) of the myelocytomatosis virus (MC29) subgroup of avian acute leukemia viruses. Hence, OK10 is classified as a member of the MC29 subgroup of avian tumor viruses, in agreement with classification based on its oncogenic spectrum. The group-specific sequences of OK10 RNA include partial (Δ)
pol
and
env
genes, a
c
-region, and, unlike those of all other members of the MC29 subgroup, a complete
gag
gene. Oligonucleotide mapping revealed 5′-
gag
-Δ
pol
-
mcv
-Δ
env
-
c
-3′ as the order of the subgroup-specific and group-specific elements of OK10 RNA. The genetic unit
gag
-Δ
pol
-
mcv
, measuring ≈6.4 kilobases, codes for the nonstructural, presumably transforming, 200,000-dalton OK10-specific protein and also includes the
gag
gene coding for the internal virion proteins. Because
gag
is the only intact virion gene shared in addition to regulatory RNA sequences between OK10 and nondefective avian tumor viruses, it is concluded that the
gag
gene is sufficient for the formation of a defective virus particle. Comparisons among the RNAs and gene products of different viruses of the MC29 subgroup show that they share 5′-terminal
gag
-related and internal
mcv
sequences but differ from each other in intervening
gag
-,
pol
-, and
mcv
-related sequences. It follows that the probable transforming genes and their protein products have two essential domains, one consisting of conserved 5′
gag
-related and the other of 3′
mcv
-related sequence elements. In the light of this and previous knowledge we can now distinguish two designs among five different transforming
onc
genes of avian tumor viruses:
onc
genes with coding sequences unrelated to virion genes, like those of Rous sarcoma virus and avian myeloblastosis virus, and
onc
genes with coding sequences that are hybrids of virion genes and specific sequences, like those of the MC29 subgroup viruses, of avian erythroblastosis virus, and of Fujinami sarcoma virus.
Electron tunneling process and the segment mobility of macromolecules.
Authors: Chernavskii D S , Frolov E N , Goldanskii V I , Kononenko A A , Rubin A B
Published: May 2006

New experimental data [Berg, A. I., Noks, P. P., Kononenko, A. A., Frolov, E. N., Khrymova, I. N., Rubin A. B., Likhtenstein, G. I., Goldanskii, V. I., Parak, F., Bukl, M. & Mössbauer, R. (1979) Mol. Biol. (USSR) 13, 81-89; Berg, A. I., Noks, P. P., Kononenko, A. A., Frolov, E. N., Uspenskaya, N. Y., Khrymova, I. N., Rubin, A. B., Likhtenstein, G. I. & Hideg, K. (1979) Mol. Biol (USSR) 13, 469-477] provide evidence that the electron tunneling process is connected to a special type of conformational transition (segmental transition) protein macromolecules in photosynthetic membranes. This problem is investigated with a simple mechanical model. It is shown that the segmental degree of freedom can play the role of the strongly interacting accepting mode for the electron tunneling process. The temperature dependences of the electron tunneling rate and the recoilless gamma-ray absorption of membrane-bound 57Fe, as an indicator of the intramolecular mobility, are calculated. The problem of energy storage in proteins is also discussed.
Magneto-orientation of lecithin crystals.
Authors: Sakurai I , Kawamura Y , Ikegami A , Iwayanagi S
Published: May 2006

For the purpose of clarifying the magneto-orientation mechanism of several biological membrane systems, xylene-suspended thin-layered single crystals of lecithin, which is a major component of membranes, were subjected to magnetic fields of various strengths, and the orientation behavior of the crystals was analyzed. Lecithin crystals oriented in such a way that the directions of both the hydrocarbon chains and the phosphorylcholine group of the lecithin molecule were perpendicular to the magnetic field, suggesting that the crystals were diamagnetically biaxial. In contrast, hydrocarbon chains of phospholipids in many biological membranes are known to orient parallel to magnetic fields. The value of the volume diamagnetic susceptibility anisotropy, delta chi (i.e. the difference between susceptibilities parallel and perpendicular to the direction of the hydrocarbon chain in the lecithin crystals), estimated from the magneto-orientation behavior was about -9 X 10(-8) cgs. This is distinctly larger than that of vesicles of egg yolk lecithin measured by Boroske and Helfrich [Boroske, E. & Helfrich, W. (1978) Biophys. J. 24, 863-868] and also larger than that of single crystals of polyethylene, which was measured for comparison by the same technique as that used for lecithin in this study. The differences between these values of delta chi seem to result from the contribution of the polar head (i.e., the part of the lecithin molecule other than the two hydrocarbon chains), which is ordered, less ordered, or deleted in the respective cases above, although mainly from the contribution of the hydrocarbon chains, which are ordered in crystals and disordered in vesicles.
Alteration of lymphocyte surface properties by insertion of foreign functional components of plasma membrane.
Authors: Prujansky-Jakobovits A , Volsky D J , Loyter A , Sharon N
Published: May 2006

We report the successful coreconstitution of solubilized lymphocyte plasma membranes and Sendai virus envelopes into membrane vesicles that possess the ability to fuse efficiently with mouse splenocytes of thymocytes to give fully viable cells with modified surface properties. Integration of donor membrane components into the acceptor cells was demonstrated by chemical, morphological, and immunological methods. Over 40% of the label from vesicles coreconstituted with radiolabeled (with 125I or 3H) lymphocyte membranes was incorporated into the fused cells. Insertion of biotin-labeled membrane components into the membranes of the acceptor cells was shown by electron microscopy with ferritin-conjugated avidin. Transfer of receptors to soybean agglutinin was also demonstrated. When vesicles from thymocyte membranes were fused with B splenocytes, over 50% of the cells were lysed with anti-theta antiserum and complement. Moreover, lymphocytes into which allogeneic membranes were incorporated triggered the autologous cells in the mixed lymphocyte reaction, indicating the functional transfer of major histocompatibility complex antigens. These findings strongly suggest that the transferred membranes were functionally incorporated into the acceptor cell membranes. The technique described opens new ways for elucidation of the role of the lymphocyte membrane in the immune response as well as for the understanding of the structure-function relationship of membrane components in other cells.
Distribution of virus structural proteins and protein-protein interactions in plasma membrane of baby hamster kidney cells infected with Sindbis or vesicular stomatitis virus.
Authors: Scheefers H , Scheefers-Borchel U , Edwards J , Brown D T
Published: May 2006

The plasma membrane of baby hamster kidney (BHK-21) cells infected with either Sindbis or vesicular stomatitis virus was isolated by a technique involving the ingestion of latex beads by the cells. Plasma membrane isolated from Sindbis virus-infected cells contained only one (E1) of the three (E1, E2, and C) structural proteins of this virus. When the latex beads were pretreated with either polylysine or DEAE-dextran, plasma membrane obtained from Sindbis virus-infected cells contained all three structural proteins and PE2, a precursor to one of the structural proteins. In pulse-chase radiolabeling experiments with Sindbis virus-infected cells, it was possible to follow the appearance of the precursor protein (PE2) i the plasma membrane and its eventual conversion to E2. The appearance of Sindbis virus membrane proteins PE2 and E1 in the purified plasma membrane was not affected by the drug tunicamycin, an inhibitor of glycosylation. These experiments imply the following: (i) Cleavage of the Sindbis virus precursor polypeptide PE2 to E2 is not a prerequisite for its transport to the cell plasma membrane; (ii) transport of virus membrane proteins to the cell surface does not depend on glycosylation; and (iii) although all Sindbis virus structural proteins are associated with the plasma membrane, a generally accepted pairing of PE2-E1 or E2-E1 in the plasma membrane either does not exist or, if it does exist, involves a very weak interaction. The procedures used in this study also resulted in the successful isolation of plasma membrane from vesicular stomatitis virus-infected cells containing the glycoprotein, the matrix protein, and the nucleocapsid protein, a result that suggests that these proteins are located on the media side of baby hamster kidney cells grown in monolayer.
Molecular limits on the size of a genetic locus in Drosophila melanogaster.
Authors: McGinnis W , Farrell J , Beckendorf S K
Published: May 2006

This report places outer limits on the size of the DNA region required for expression of a Drosophila gene. This region, termed the unit of expression, includes not only the structural gene but also any cis-acting sequences that modulate its activity. The locus we have chosen, Sgs-4, codes for one of the glue proteins secreted by larval Drosophila salivary glands. Cytological deficiencies have been identified that eliminate sequences on one side or the other of Sgs-4 without affecting its expression. The ends of these deficiencies have been localized accurately with respect to restriction endonuclease sites in and near the locus. These endpoints limit the Sgs-4 structural gene and essential flanking sequences to a 16- to 19-kilobase region of the X chromosome. The results also show that there is no DNA sequence rearrangement in the Sgs-4 region during development of either the polytene larval salivary glands or adult flies.
Identification of human eosinophil lysophospholipase as the constituent of Charcot-Leyden crystals.
Authors: Weller P F , Goetzl E J , Austen K F
Published: May 2006

Since the initial descriptions of Charcot-Leyden crystals more than 100 years ago, the presence of these slender, dipyramidal crystals in human tissues and biologic fluids has become a hallmark of eosinophilic leukocyte infiltration, especially in association with allergic and helminthic diseases. The formation of these crystals in vitro after disruption of human eosinophils, but not of other cell types, in hypotonic saline or detergent established the eosinophil as the unique cellular source of the crystalline protein. Charcot-Leyden crystals have now been found to express lysophospholipase activity (lysolecithin acylhydrolase, EC 3.1.1.5), and the solubilized Charcot-Leyden crystal protein presents a single stained protein band that is coincident with the lysophospholipase activity eluted from replicate gels on alkaline polyacrylamide gel electrophoresis. On sodium dodecyl sulfate/polyacrylamide gel electrophoresis, the solubilized Charcot-Leyden crystal protein migrates with a molecular weight of 17,400, which is comparable to that of eosinophil lysophospholipase purified chromatographically to homogeneity; further, on combination, the two proteins comigrate as a single staining band. Finally, the chromatographically purified eosinophil lysophospholipase in hypotonic buffer forms dipyramidal crystals morphologically identical to Charcot-Leyden crystals. The findings that chromatographically purified, homogeneous eosinophil lysophospholipase and Charcot-Leyden crystal protein express the same enzymatic activity, are of the same size and charge, and form crystals of identical morphology indicate that human eosinophil lysophospholipase is the constituent of Charcot-Leyden crystals.
Diazepam receptor: specific nuclear binding of [3H]flunitrazepam.
Authors: Bosmann H B , Penney D P , Case K R , Averill K
Published: May 2006

Autoradiographic localization of [3H]flunitrazepam in nuclei of the rat cerebral cortex was further confirmed by biochemical analysis of specific nuclear binding. Highly purified rat cerebral cortex nuclei were shown to bind [3H]flunitrazepam specifically. The Kd(app) for nuclear binding was 28 nM for the nuclei compared with a Kd(app) of 1.1 nM for binding of [3H] flunitrazepam to synaptosomal membrane fractions of the same tissue. Inhibition of the nuclear binding with inosine and hypoxanthine was greater than inhibition of the synaptic membrane fractions. These results lead to to conclude that specific binding may occur at both the synaptic membrane and the nuclear levels and that different endogenous ligands may compete at each site for binding. Furthermore, the possibility exists for translocation and alteration of the bound ligand complex from membrane site to nuclear site.
Conserved densities
Authors: Case K. M.
Published: May 2006

Conserved densities for Hamiltonian systems are shown to satisfy simple linear equations. These are essentially the original equations linearized around a particular solution. A number of examples are displayed, which pertain to many systems of physical interest.
Rearrangement of immunoglobulin gamma 1-chain gene and mechanism for heavy-chain class switch.
Authors: Kataoka T , Kawakami T , Takahashi N , Honjo T
Published: May 2006

Cloning and nucleotide sequence determination suggest that the rearranged gamma 1-chain gene in a gamma 1-chain-producing myeloma a-pears to be formed by the recombination between the 5' flanking regions of the gamma 1- and mu-chain genes of undifferentiated cells. The recombination site is distinct from the putative J region and is a novel region that we call the S region. We have extended our previous model that explains the heavy-chain class switching by two or more successive recombination events.
Fluorescence energy transfer studies on the active site of papain
Authors: Henes Jill B. , Briggs Martha S. , Sligar Stephen G. , Fruton Joseph S.
Published: May 2006

Measurements have been performed of the excited-state lifetimes and fluorescence yields of papain tryptophan units when acyl derivatives of Phe-glycinal are bound at the active site of the enzyme. The enhancement of tryptophan fluorescence in complexes of papain with the acetyl or benzyloxycarbonyl derivatives is not stereospecific with respect to the configuration of the phenylalanyl residue, and the L and D isomers are equally effective as active-site-directed inhibitors of papain action. Evidence is offered in favor of the conclusion that this enhancement is primarily a consequence of the interaction of the phenylalanyl side chain of the inhibitor with Trp-69 of the enzyme. This residue can exchange fluorescence energy with the other four tryptophans of papain (Trp-7, Trp-26, Trp-177, Trp-181) upon excitation near their absorption maxima, but such “homotransfer” is absent if they are excited at the long-wave edge of their absorption spectra. Crystallographic data indicate that Trp-26 is most favorably positioned for efficient energy exchange with Trp-69, and the fluorescence data have been used to calculate a distance of 11 Å between the two residues; this value is in satisfactory agreement with that found by crystallography. When derivatives of Phe-glycinal bearing an amino-terminal mansyl [6-(
N
-methylanilino)-2-naphthalene sulfonyl] group are bound at the active site of papain, the tryptophan fluorescence is quenched, as compared with that of the complex of papain with acetyl-Phe-glycinal, indicating energy transfer from papain tryptophan (most probably via Trp-26) to the fluorescent probe group. Although the L and D isomers of mansyl-Phe-glycinal are equally effective as inhibitors of papain action, the fluorescence quenching by the two isomers is different.
Electron microscope study of the kinetics of the fiber-to-crystal transition of sickle cell hemoglobin.
Authors: Wilson S M , Makinen M W
Published: May 2006

The intermediates and the rate-limiting step in the crystallization of deoxygenated sickle hemoglobin have been determined by a kinetic study with the use of electron microscopy. In slowly stirred solutions of deoxygenated hemoglobin S [Pumphrey, J. & Steinhardt, J. (1977) J. Mol. Biol. 112, 359--375], the sequential appearance of fibers have a diameter of approximately equal to 210 A, bundles of aligned fibers in well-ordered arrays, "thick" fibers of approximately equal to 470 A diameter, and microcrystals is observed. Only the fibers having a diameter of approximately equal to 210 A and bundles of aligned fibers are assigned as kinetically important intermediates of the fiber-to-crystal transition. Addition of microscopic seed crystals obtained from slowly stirred solutions of deoxyhemoglobin S to a solution composed of only fibers and hemoglobin monomers results in more rapid crystallization than in control solutions. Addition of seed crystals after the formation of bindles of aligned fibers does not alter the overall kinetics of crystallization. The results demonstrate that alignment of fibers is the rate-limiting step in the crystallization process and results in formation of nucleation sites for crystal growth.
A human protein related to the major envelope protein of murine mammary tumor virus: identification and characterization.
Authors: Dion A S , Farwell D C , Pomenti A A , Girardi A J
Published: May 2006

A human milk protein was isolated to apparent homogeneity and shown to be immunologically related to gp55, the major envelope glycoprotein of murine mammary tumor virus. Through the development of ultrasensitive protocols, which have wide applicability, immunological relatedness was corroborated by the demonstration of homologous protein sequences between the human and viral proteins.
A small RNA induced late in simian virus 40 infection can associate with early viral mRNAs.
Authors: Alwine J C , Dhar R , Khoury G
Published: May 2006

Analysis of total cytoplasmic and polyadenylylated cytoplasmic RNA from cells lytically infected with simian virus 40 (SV40) has demonstrated the presence of a small RNA, approximately 65 nucleotides long, that is induced late in lytic infection. This small RNA is apparently specific in size and sequence and is not selected on columns of oligo(dT)-cellulose. It is homologous to a region of the early SV40 mRNAs (and to the late DNA strand), starting approximately 250 nucleotides from the 3' end of the early mRNAs (SV40 map position 0.21). The function of this RNA in the viral cycle and its source are unknown at this time; however, its temporal expression, unique sequence, and interesting region of homology within the SV40 genome suggest a possible role in the control of SV40 gene expression.
Functional characteristics of human T-cell subpopulations distinguished by a monoclonal antibody
Authors: Engleman Edgar G. , Benike Claudia , Osborne Barbara , Goldsby Richard
Published: May 2006

In animals and in man, diverse immunologic functions are mediated by specialized T-cell (thymus-derived lymphocyte) subsets that are distinguishable from one another on the basis of differences in cell surface determinants. Unfortunately, in humans, subset-specific antibodies have been difficult to generate. In this study, production of a murine monoclonal antibody specific for a subset of human T cells was achieved by fusing a sensitized B cell (bone marrow-derived cell) with a myeloma cell and isolating the antibody secreted by the resultant hybrid clone. This antibody binds 30-35% of peripheral T lymphocytes (T
a
+
cells) but fails to bind remaining T lymphocytes (T
a
-
cells), B lymphocytes, or monocytes. T
a
+
and T
a
-
subpopulations were separated with a fluorescence-activated cell sorter and their
in vitro
responses to various stimuli were assessed. T
a
+
and T
a
-
cells respond equally well to soluble antigens, allogeneic B cells, and autologous B cells, but only T
a
+
cells respond to concanavalin A. T
a
+
cells cultured in the presence of concanavalin A gradually lose the T
a
marker, an effect not observed after stimulation with phytohemagglutinin, soluble antigens, or alloantigens. These results suggest that the functional subpopulation of T cells defined by T
a
does not correspond to any previously described human T cell subset. Furthermore, somatic cell hybridization has been shown to be a feasible method for production of monoclonal antibodies specific for subpopulations of human lymphocytes.
Comparative tryptic peptide mapping studies suggest a role in cell transformation for the gag-related protein of avian erythroblastosis virus and avian myelocytomatosis virus strains CMII and MC29.
Authors: Kitchener G , Hayman M J
Published: May 2006

The gag-related proteins found in cells transformed by avian erythroblastosis virus (AEV) and the avian myelocytomatosis viruses MC29 and CMII have been compared by tryptic peptide fingerprinting. A comparison of the methionine-containing tryptic peptides of the AEV 75-kilodalton protein, the CMII 90-kilodalton protein, and the MC29 110-kilodalton protein with the gag gene product Pr76 of their naturally occurring helper leukemia viruses enabled us to distinguish those peptides related to the gag gene from the non-gag-related peptides. The 12 non-gag peptides found in the AEV 75-kilodalton protein were unique to this protein and not found in the MC29 110-kilodalton or CMII 90-kilodalton proteins. In contrast, the MC29 110-kilodalton protein shared two methionine-containing non-gag tryptic peptides with the CMII 90-kilodalton protein. When these experiments were repeated with [14C]lysine and [14C]arginine as the labeled amino acids, the MC29 110-kilodalton protein and the CMII 90-kilodalton protein were found to share 30 out of approximately 40 non-gag-related peptides. These results demonstrate that viruses with a similar transformation spectrum synthesize related proteins and suggest that the gag-related proteins represent the transforming proteins of the replication-defective avian leukemia viruses.
Quantal release of acetylcholine examined by current fluctuation analysis at an identified neuro-neuronal synapse of Aplysia.
Authors: Simonneau M , Tauc L , Baux G
Published: May 2006

Quantal events have been analyzed at a neuro-neuronal synapse of Aplysia where the nature of the transmitter is established and both presynaptic and postsynaptic neurons are identified and can be voltage-clamped. Prolonged depolarizations were applied to the presynaptic neuron, which gave rise in the postsynaptic cell to a current response characterized by current fluctuations or noise. Acetylcholine was also applied ionophoretically on the same postsynaptic cell. Amplitude and time course of miniature currents and acetylcholine-activated chloride channels of the same cell were examined by using a current fluctuation analysis. It was estimated that one presynaptic spike releases about 180 quanta, each opening 500 chloride channels.
Guided solitary waves
Authors: Miles John
Published: May 2006

Transversely periodic solitary-wave solutions of the Boussinesq equations (which govern wave propagation in a weakly dispersive, weakly nonlinear physical system) are determined. The solutions for negative dispersion (e.g., gravity waves) are singular and therefore physically unacceptable. The solutions for positive dispersion (e.g., capillary waves or magnetosonic waves in a plasma) are physically acceptable except in a limited parametric interval, in which they are complex. The two end points of this interval are associated with (two different) resonant interactions among three basic solitary waves, two of which are two-dimensional complex conjugates and the third of which is one-dimensional and real.
Nonexistence of global solutions of □
u
=
F
(

u
tt

) and of □
v
=
F
′(

v
t

)

v
tt

in three space dimensions
Authors: John Fritz
Published: May 2006

The symbol □ denotes the operator ∂
2
/∂
2
- Δ in three space dimensions, and
F
denotes a function with
F
(0) =
F
′(0) = 0, inf
F
″ > 0. It is shown that
u
(
x,t
) ≡ 0, if □
u
=
F
(

u
tt

) for
x
∈ R
3
,
t
≥ 0, provided

u,u
t
,u
tt

for
t
= 0 have compact support. Similarly
v
(
x,t
) ≡ 0 if □
v
=
F
′(

v
t

)

v
tt

for
x
∈ R
3
,
t
≥0, provided

v,v
t

for
t
= 0 have compact support and satisfy ∫[

v
t

-
F
(

v
t

)]
dx
≥ 0. This shows that the global existence theorem proved by S. L. Klainerman [(1980)
Commun. Pure Appl. Math.
33, in press] in more than five space dimensions is not valid for three dimensions. The theorems also imply instability at rest of certain hyperelastic materials.
Association of Mu-containing plasmids with the
Escherichia coli
chromosome upon prophage induction
Authors: Chaconas George , Harshey Rasika M. , Bukhari Ahmad I.
Published: May 2006

To determine the structure of a prophage-containing plasmid during Mu transposition, we have monitored the physical state of pSC101[unk]Mu
cts
after thermoinduction. We have also examined the fate of a mini Mu plasmid constructed
in vitro
by deleting 27 kilobases from the center of the Mu prophage in pSC101[unk]Mu
cts
. At various times after prophage induction, DNA was extracted from Mu or mini Mu plasmid-containing strains and subjected to electrophoresis in low concentration agarose gels followed by transfer of the DNA to nitrocellulose paper. Separate hybridization with
32
P-labeled pSC101 and Mu DNA revealed the position of the plasmids and the replication of Mu DNA. At times after induction when Mu replication was clearly visible, Mu and mini Mu plasmids were found to migrate with
Escherchia coli
DNA. This Mu-specific association requires the phage coded
A
and
B
proteins. Electron microscopy has shown that some of the associated DNA is comprised of circular plasmid molecules which appear to be in contact with the chromosomal DNA. These structures may represent intermediates or end products of the replication-integration process. The finding that Mu and mini Mu plasmids do not give rise to any detectable excision products and apparently remain intact during Mu transposition supports our proposal that the predominant event after Mu induction is the replication of Mu DNA
in situ
to generate integrative intermediates.
Direct measurement of bone resorption and calcium conservation during vitamin D deficiency or hypervitaminosis D
Authors: Klein Leroy
Published: May 2006

When bone is remodeled during the growth of a given size bone to a larger size, some bone is resorbed and some is deposited. Much of the resorbed bone mineral, calcium, can be reutilized during bone formation. The net and absolute effects of normal growth, vitamin D deficiency, or vitamin D excess were compared on bone resorption, bone formation, and calcium reutilization. Growing chicks were prelabeled extensively with three isotopes:
45
Ca, [
3
H]tetracycline, and [
3
H]proline. Data were obtained weekly during 3 weeks of control growth, vitamin D deficiency, or vitamin D overdosage while on a nonradioactive diet. Bone resorption as measured by increases in the marrow (inner) diameter of the midshaft of the femur and humerus and by the weekly losses of total [
3
H]tetracycline and [
3
H]collagen per whole bone was not significantly different among any of the groups studied. The data indicated that the high rate of cortical bone resorption in experimental chicks was not increased above that observed in experimental chicks was not increased above that observed in control chicks. Vitamin D deficiency had little effect on the total
45
Ca in whole bones, whereas vitamin D-treated chicks lost 40% of their
45
Ca. Thus, vitamin D overdosage resulted in a decrease of
45
Ca reutilization, whereas vitamin D deficiency resulted in an apparent increase of
45
Ca reutilization. Both vitamin D-deficient and vitamin D-treated chicks had a decreased accumulation of dietary calcium per whole bone. The insufficient mineral mass in vitamin D-deficient chicks resulted from the indirect inhibition of bone mineralization due to the low intestinal absorption of calcium rather than from a change in bone resorption. In vitamin D-treated chicks the apparent bone atrophy and net loss of
45
Ca from bone resulted from inhibiting bone matrix formation and mineralization instead of increasing bone resorption. The constancy of bone resorption under these experimental conditions suggests that bone mineralization is the major regulator of bone mass.
Limited DNase I nicking as a probe of gene conformation.
Authors: Zasloff M , Camerini-Otero R D
Published: May 2006

We have extended the use of pancreatic DNase I as a probe of chromatin structure by exploring the accessibility of an active gene to the introduction of the first single-stranded nick. We show by a target analysis that the beta-globin gene is about 25-fold more sensitive to single-site nicking than is an average sequence in the chicken erythrocyte nucleus or the nontranscribed albumin gene. The sites of initial DNase I nicking are shown to cluster within the transcribed sequence of the beta-globin gene.
Effect of introduction of small alkyl groups on mRNA function.
Authors: Fraenkel-Conrat H , Singer B
Published: May 2006

Treatment of RNA with dimethyl sulfate methylates only nitrogens, preferentially the 7 position of guanosine, whereas treatment with ethylnitrosourea ethylates mainly oxygens, preferentially the phosphodiester groups. Two plant viral mRNAs were modified with these two reagents at levels of 4-28 alkylations per molecule. The ability of alkylated RNAs to stimulate amino acid incorporation in the wheat germ system was somewhat diminished by both types of modification, but the predominant protein made, as ascertained by polyacrylamide gel electrophoresis, was the typical gene product of the respective mRNA. These data suggest that random alkylations, mostly of either the guanosine N-7s or the phosphates, do not interfere with peptide chain elongation, but that the ability to initiate translation properly is affected by these substitutions, presumably through their effect on the conformation of the RNAs.
Expression of peanut agglutinin receptors on virus-induced preleukemic cells in mice.
Authors: Reisner Y , Sharon N , Haran-Ghera N
Published: May 2006

Preleukemic bone marrow and spleen cells of irradiated C57BL/6 mice that were inoculated with the radiation-induced leukemia virus variant D-RadLV differ from autonomous end-stage leukemia cells in the expression of the receptor for peanut agglutinin. As a result, the preleukemic cells are agglutinated by peanut agglutinin and the end-stage cells are not. This observation provides further evidence that preleukemic cells possess surface markers similar to those of the prothymocyte. In vitro and in vivo thymocyte-virus interactions reveal that cells susceptible to D-RadLV transformation are present mainly among the peanut agglutinin-receptor-bearing thymocyte population which has previously been demonstrated to be immunologically immature.
Large evoked potentials to dynamic random-dot correlograms and stereograms permit quick determination of stereopsis.
Authors: Julesz B , Kropfl W , Petrig B
Published: May 2006

The combination of three technological innovations permits the fast and objective determination of stereopsis in nonverbal subjects: (i) It is shown that dynamic random-dot correlograms (RDC) are as effective as dynamic random-dot stereograms (RDS) in eliciting large evoked potentials (EP), and that the generation of RDC is simpler than that of RDS. (ii) The presentation of RDC in the form of red-green anaglyphs is insensitive to subjects' head tilt, because alternation of correlation (binocular fusion) with uncorrelation (binocular rivalry) does not depend on the direction of binocular disparity, whereas perception of depth in RDS does. (iii) Projection TV techniques, using backprojected large screens viewed from near distances, permit noncooperative subjects (e.g., human infants or monkeys) to be surrounded with the stimulus, so they cannot look away.
Estimation and prediction for mixtures of the exponential distribution
Authors: Robbins Herbert
Published: May 2006

Let
x
be a random variable whose distribution is an unknown mixture of exponentials with different means θ. From a random sample
x
1
,...,

x
n

of
x
values we show that
E
(θǀ
x
>
a
) can be estimated for any given
a
> 0. We can therefore predict the average of all future observations taken on those
x
values in the sample that exceed
a
.
DNA synaptase: an enzyme that fuses DNA molecules at a region of homology.
Authors: Potter H , Dressler D
Published: May 2006

This paper describes an enzyme from Escherichia coli, and its purification to apparent homogeneity. The protein, which we call "DNA synaptase" and which may be representative of a class of enzymes, fuses double-stranded DNA molecules at a region of homology. In addition, the purified enzyme is able to catalyze the association of single-stranded DNA with homologous duplex DNA. The genome fusion reaction catalyzed by the purified enzyme occurs in the presence of Mg2+, spermidine, and 2-mercaptoethanol and does not require a high-energy cofactor. By bringing two genomes together at a region of homology, DNA synaptase has a property expected for an enzyme that participates in an early step in genetic recombination. However, the synaptase can be recovered from Rec A- cells, and thus it is not yet possible to determine whether this enzyme plays a role in physiological recombination or in another cellular process that involves genome fusion, such as the recombinational repair of damaged DNA.