bluuebunny/crossref_metadata_2025 huggingface dataset:
The persisting (P) cell: histamine content, regulation by a T cell-derived factor, origin from a bone marrow precursor, and relationship to mast cells.
Authors: Schrader J W , Lewis S J , Clark-Lewis I , Culvenor J G
Published: May 2006

Histamine was detected at levels of 100 ng/10(6) cells in the metachromatic granules of the persisting (P) cell, which appears in cultures of murine lymphoid or bone marrow cells and is capable of long-term growth in vitro in the presence of a T cell-derived growth factor. This factor, which we termed P-cell stimulating factor, was distinct from t-cell growth factor and had an apparent molecular weight of 25,000-30,000. P cells did not originate from Thy.1-positive cells nor was the thymus necessary for the development of their precursors. Moreover, P cells grew directly from colonies generated in agar cultures of bone marrow cells, the nature of the colonies indicating that P cells shared a common precursor with hemopoietic cells. Mutant Wf/Wf mice, although deficient in certain mast cells, possessed P-cell precursors. It is hypothesized that P cells are related to a specialized subset of mast cells, derived from a bone marrow progenitor but regulated by activated T cells.
Fracture-label:O cytochemistry of freeze-fracture faces in the erythrocyte membrane.
Authors: Pinto da Silva P , Parkison C , Dwyer N
Published: May 2006

A method--"fracture label"--is described for the cytochemical labeling of the membrane faces produced by freeze-fracture. Human erythrocytes embedded in a crosslinked matrix are frozen, fractured in liquid nitrogen, thawed, labeled, and cut into thin sections. Electron microscope observation of the fracture faces shows preferential partition of concanavalin A binding sites with the inner half of the membrane. This signifies that, during freeze-fracture, binding sites are dragged from the outer surface across the outer ("exoplasmic") half of the membrane and retained on the protoplasmic fracture face (face P). The fracture process results in exposure of new anionic sites on face P. Fracture-label can be applied to the cytochemical characterization of the cellular components exposed by freeze-fracture of isolated cells and tissues.
Ontophyletics of the nervous system: eyeless mutants illustrate how ontogenetic buffer mechanisms channel evolution.
Authors: Katz M J , Lasek R J , Kaiserman-Abramof I R
Published: May 2006

Genetics and molecular biology have shown the mechanisms that allow the genome to provide both the continuity and the variation from generation to generation within a phylogeny. Embryology and developmental biology show the mechanisms that turn the genome into an organism. Mutations, the basis for evolutionary change, cannot in themselves ensure concordance between their products and the products of unchanged genes. Thus, mutations will not necessarily produce a viable organism. On the other hand, ontogenetic buffer mechanisms normally maintain concordance in the developing organism. In addition, ontogenetic buffer mechanisms can integrate discordant mutations into viable organisms that can then be perpetuated during evolution. The evolutionary role of one ontogenetic buffer mechanism, compensatory innervation, is well illustrated in the anopthalmic mutant mouse. In the anopthalmic mouse, a single gene mutation removes afferent axons of the dorsal lateral geniculate nucleus, and compensatory innervation by another population of axons ensures that the dorsal lateral geniculate remains integrated into the central nervous system. Within each organism's ontogeny is a hierarchy of sources of compensatory innervation, and this hierarchy will determine how any particular deafferentating mutation will be buffered. In this way, an ontogeny can channel the phylogeny of which it is a member.
Genetics of cell surface receptors for bioactive polypeptides: variants of Swiss/3T3 fibroblasts resistant to a cytotoxic chimeric insulin.
Authors: Miskimins W K , Shimizu N
Published: May 2006

Insulin crosslinked to the catalytic fragment A of diphtheria toxin has previously been shown to be cytotoxic to insulin-responsive mouse BALBc/3T3 cells but noncytotoxic to insulin-nonresponsive variant IN-2 cells [Miskimins, W. K. & Shimizu, N. (1979) Biochem. Biophys. Res. Commun. 91, 143-151]. We have now used this cytotoxic chimeric insulin to select resistant variants of Swiss/3T3 fibroblasts. Of eight resistant colonies isolated, two proved to be deficient in insulin receptor and exhibited altered morphologies and growth rates. These variants, however, retained the ability to bind and respond to epidermal growth factor. Thus, this selection technique is effective for the isolation of variants specifically related to cellular binding and processing of insulin. Such variants will be advantageous for the genetic and biochemical characterization of the mechanism of insulin's action.
Osmotic control of kdp operon expression in Escherichia coli.
Authors: Laimins L A , Rhoads D B , Epstein W
Published: May 2006

Turgor pressure, the difference in osmotic pressure across the inner membrane, has been found to regulate expression of the kdp operon in Escherichia coli. The kdp operon codes for a high-affinity repressible transport system for the uptake of potassium. We have studied the regulation of Kdp expression in a strain in which the gene for beta-galactosidase, lacZ, was placed under control of the kdp promotor. Neither internal nor external K+ concentrations directly controlled Kdp expression. Only when the external K+ concentration was reduced to the point of limiting growth was the kdp operon expressed. An increase in external osmolarity at constant K+ concentration, a procedure that reduces turgor pressure, caused expression of the kdp operon. As the magnitude of the osmotic shift was increased, corresponding to greater decreases in turgor pressure, the amount of Kdp expression also increased. The kdp operon thus appears to be controlled by changes in a physical force, the turgor pressure.
Complementation of gene deletions by cell hybridization.
Authors: Cori C F , Gluecksohn-Waelsch S , Klinger H P , Pick L , Schlagman S L , Teicher L S , Wang-Chang H F
Published: May 2006

Overlapping deletions in chromosome 7 of the mouse are responsible for activity deficiencies of various liver-specific enzymes, including tyrosine aminotransferase (TAT). In an effort to elucidate the nature and type of action of the deleted genes, somatic cell hybridization experiments were carried out. Enzyme-deficient liver cells of homozygous mutant mice or normal liver cells of control newborn mice were hybridized with 2S Faza rat hepatoma cells and the hybrid cell colonies were analyzed for TAT activity, The results show the presence of inducible mouse TAT activity in mutant-2S Faza hybrid cells, thereby excluding the possibility that the structural gene for TAT is included in the gene sequences deleted in the mutants. Furthermore, determinations of mouse glucose-6-phosphate isomerase 1 as a marker eliminate chromosome 7 as the possible carrier of the TAT structural gene, which therefore appears to map on a different chromosome. The deletions interfering with normal enzyme activities apparently include genes other than the respective structural genes, namely those with essential functions in controlling the expression of the differentiated state of the liver cell.
Interaction of human diferric transferrin with reticulocytes.
Authors: Huebers H , Csiba E , Josephson B , Huebers E , Finch C
Published: May 2006

Methods have been devised for preparing human transferrin with a different isotope of iron selectively labeling each of the two iron binding sites and for determining the distribution of radioiron among transferrin molecules. When diferric human transferrin was exposed to human or animal reticulocytes, there was an equal contribution of radioiron from the acid-stable and acid-labile sites. In this delivery, both atoms of iron were removed simultaneously from the diferric transferrin molecule, converting it to apotransferrin. At similar iron concentrations the amount of iron delivered by diferric transferrin was twice that delivered by monoferric transferrin.
Fructose-bisphosphatase as a substrate of cyclic AMP-dependent protein kinase.
Authors: Hosey M M , Marcus F
Published: May 2006

We have tested rat liver fructose-bisphosphatase (D-fructose-1,6-bisphosphate 1-phosphohydrolase, EC 3.1.3.11) and three other gluconeogenic fructose-bisphosphatases as substrates for the catalytic subunit of cyclic AMP-dependent protein kinase. In contrast to the rat liver enzyme, homogeneous preparations of mouse liver, rabbit liver, and pig kidney fructose-bisphosphatase could not be phosphorylated by the kinase. Comparative sodium dodecyl sulfate/polyacrylamide gel electrophoresis of the four above fructose-bisphosphatases revealed that the subunit molecular weight of the isolated rat liver enzyme (ca. 40,000-42,000) was greater than that of mouse liver, rabbit liver, and pig kidney fructose-bisphosphatases (ca. 36,000-37,000). Treatment of 32P-labeled rat liver fructose-bisphosphatase with trypsin resulted in the conversion of the rat liver enzyme to an active species with a subunit molecular weight identical to that of the three other enzymes, with complete loss of the 32P-labeled site. Identical trypsin treatment of pig kidney fructose-bisphosphatase caused no change in the molecular weight of the enzyme. The results suggest that the purified mouse liver, rabbit liver, and pig kidney fructose-bisphosphatases are not substrates for the cyclic AMP-dependent protein kinase in vitro because they lack the phosphorylation-site peptide.
Use of whole-cell fixation to visualize replicating and maturing simian virus 40: identification of new viral gene product.
Authors: Jackson V , Chalkley R
Published: May 2006

Formaldehyde fixation of simian virus 40 (SV40)-infected CV-1 cells at appropriate times after infection permits us to isolate crosslinked complexes of SV40 minichromosomes during the time of DNA replication and during packaging with viral proteins. Such crosslinked complexes can be separated on the basis of density on CsCl/guanidine . HCl density gradients. During the course of these studies we observed the presence of a low molecular weight protein in a region of the gradient much enriched with viral nucleoproteins. This protein is present only in infected cells and has a molecular weight and amino acid composition consistent with it being the product of the so-called SV40 agnogene.
Carcinogen-mediated amplification of viral DNA sequences in simian virus 40-transformed Chinese hamster embryo cells.
Authors: Lavi S
Published: May 2006

Exposure of simian virus 40 (SV40)-transformed Chinese hamster embryo cells to various chemical and physical carcinogens induced SV40 DNA synthesis. Although the carcinogen-mediated amplification of SV40 DNA is regulated by the viral A gene, the induction of viral DNA synthesis does not result in the rescue of infectious virus or the formation of complete viral DNA molecules. Instead, a heterogeneous collection of DNA molecules containing SV40 sequences was generated by treatment with 7,12-dimethylbenz[a]anthracene. Restriction enzyme analysis of the amplified DNA molecules in the Hirt supernatant showed that not all sequences in the integrated SV40 inserts are present. The possibility that amplification of SV40 sequences is a reflection of a general-gene-amplification phenomenon mediated by carcinogens is discussed.
Classification of multiple morphine and enkephalin binding sites in the central nervous system.
Authors: Wolozin B L , Pasternak G W
Published: May 2006

Detailed competitive displacement curves of 3H-labeled [D-Ala2,Met5]enkephalinamide, [D-Ala2,D-Leu5]enkephalin, and dihydromorphine by a series of opiates and enkephalins are biphasic, suggesting multiple sites. After treatment of tissue with naloxazone, the displacement of the three 3H-labeled ligands by all opiates and enkephalins tested becomes monophasic, losing the high-affinity displacement seen with low concentrations of both opiates and enkephalins. Coupled with Scatchard analysis of saturation experiments, these findings suggest a common site that binds both opiates and enkephalins equally well and with highest affinity (Kd values, less than 1 nM). Termed the mu 1 site, it corresponds to the previously described high-affinity site and appears to be the site responsible for analgesia under normal circumstances. The low-affinity binding of [3H]dihydromorphine (Kd, 3 nM) remaining after naloxazone treatment differs dramatically from low-affinity [D-Ala2,D-Leu5]-[3H]enkephalin binding (Kd, 5 nM). The mu 2 site, corresponding to the low-affinity [3H]dihydromorphine receptor sites, binds morphine (Ki, 10 nM) and dihydromorphine (Kd, 3 nM) far better than [D-Ala2,D-Leu5]enkephalin (Ki, 50 nM). Low-affinity [D-Ala2,D-Leu5]-[3H]enkephalin receptor sites bind [D-Ala2,D-Leu5]enkephalin (Ki, 5-8 nM) more potently than morphine (Ki, 71 nM) and correspond to the previously established delta receptor.
DNA sequence analysis reveals extensive homologies of regions preceding
hsp70
and αβ heat shock genes in
Drosophila melanogaster
Authors: Hackett Roger W. , Lis John T.
Published: May 2006

Two kinds of RNA are synthesized at the
87C1
chromosomal locus of
Drosophila melanogaster
in response to heat shock. One of these codes for the major heat shock protein, hsp70; the other, αβ RNA, derives from tandemly repeated αβ units consisting of adjacent α and β DNA elements and has no identified translation product. Another DNA element, γ, flanks the 5′ ends of some αβ units. Here we report the complete nucleotide sequence of the 617-base-pair α and the 733-base-pair γ element as well as a portion of the longer β element. Sequence comparisons between the γ element and the two
hsp70
genes at
87C1
reveal that the 406 base pairs of γ immediately upstream from the 5′ end of the αβ unit exhibit 97.5% homology with the sequences at and upstream from the 5′ end of the
hsp70
genes. A similar homology also exists between γ and an
hsp70
gene present at another heat shock locus,
87A7
, which contains no αβ units. These results, in conjunction with previous observations, strongly suggest that the coordinate induction by heat shock of the
hsp70
and αβ genes is a consequence of their homologous 5′ flanking sequences. We propose that this extraordinary degree of sequence conservation stems from the recent transposition of αβ DNA to the
87C1
locus, an event that brought αβ sequences adjacent to, and under the regulation of, the
hsp70
control element.
Coordination environment of the active-site metal ion of liver alcohol dehydrogenase.
Authors: Makinen M W , Yim M B
Published: May 2006

The coordination environment of the catalytically active metal ion of horse liver alcohol dehydrogenase (alcohol:NAD+ oxidoreductase, EC 1.1.1.1) has been investigated by electron paramagnetic resonance (EPR) methods with use of the active-site-specific Co2+-reconstituted enzyme. The EPR absorption spectrum of the metal-substituted enzyme is characteristic of a rhombically distorted environment. The spectrum of the enzyme--NAD+ complex shows approximate axial symmetry of the metal ion site, indicating that binding of the coenzyme induces a structural alteration in the active-site region. This environment is not significantly altered further by binding of the competitive inhibitor pyrazole. To assign the coordination number of the active-site metal ion, the zero-field splitting was determined on the basis of the temperature dependence of the spin--lattice relaxation of the Co2+ ion. The zero-field splitting energies are approximately 9 cm-1 for the free Co2+-reconstituted enzyme and approximately 46 and approximately 47 cm-1 for the enzyme--NAD+ and enzyme--NAD+--pyrazole complex, respectively. On the basis of studies of structurally defined small molecule complexes, these values are compatible with a tetracoordinate metal ion in the active site of the free enzyme but a pentacoordinate metal ion in the binary enzyme--NAD+ complex and in the ternary enzyme--NAD+--inhibitor complex and, therefore, presumably also in the catalytically active ternary enzyme--NAD+--alcohol complex formed in the course of alcohol oxidation.
Fibronectin-like protein in Porifera: its role in cell aggregation.
Authors: Labat-Robert J , Robert L , Auger C , Lethias C , Garrone R
Published: May 2006

Experiments were carried out on a freshwater sponge (Ephydatia mulleri) in order to demonstrate the presence of fibronectin in Porifera. By using antibodies to highly purified human plasma fibronectin, the presence of a similar or identical protein could be demonstrated in the membranes of E. mulleri cells such as epithelial cells, fibroblast-like cells, and choanocytes. The reaction was specific, could be abolished by the addition of excess fibronectin, and was not observed with nonimmune rabbit serum. The immune fluorescent reaction became stronger when the sponge cells were pretreated with acetone and could also be observed, although with a less intense staining, on the intercellular matrix. This shows the predominant presence of a sponge fibronectin-like protein in the cell membranes and also its presence to a lesser extent in the intercellular matrix. When dissociated sponge cells were led to reassociate under the microscope, reassociation could be completely inhibited by anti-human fibronectin antiserum up to a dilution of 1:120 and partially inhibited up to a dilution of 1:240. The reassociation of dissociated sponge cells could also be inhibited by the addition of purified gelatin but not with serum albumin or with a normal, nonimmune rabbit serum. These results clearly indicate that a sponge cell fibronectin-like protein may play an important role as the (or one of the) recognition site(s) of the aggregation factor(s) and can therefore be directly involved in cell association, morphogenesis, and differentiation.
Molecular cloning of a mouse submaxillary gland renin cDNA fragment.
Authors: Rougeon F , Chambraud B , Foote S , Panthier J J , Nageotte R , Corvol P
Published: May 2006

The mRNA encoding mouse renin has been partially purified from total poly(A)-containing RNA of submaxillary glands of male Swiss mice. Corresponding cDNAs were cloned in the Pst I site of pBR322. Recombinants have been characterized by differential screening and hybrid-arrested translation. The DNA of clone pRn3-5 has been used to study the expression of renin mRNA in the submaxillary gland and in the kidney of different mouse strains. The renin mRNA from submaxillary gland and kidney have the same length (1600 nucleotides) and appear to be the products of the same gene. In vitro translation of mRNAs and RNA blotting experiments have shown that renin mRNA sequences are accumulated in the submaxillary gland of males of AKR and Swiss strains but not in the gland of male BALB/c.
Suppressor factor from a T cell hybrid inhibits delayed-type hypersensitivity responses to azobenzenearsonate.
Authors: Whitaker R B , Nepom J T , Sy M S , Takaoki M , Gramm C F , Fox I , Germain R N , Nelles M J , Greene M I , Benacerraf B
Published: May 2006

By using polyethylene glycol 1540, BW5147 AKR T lymphoma cells were fused with splenocytes from A/J mice treated so as to induce suppressor T cells specific for azobenzenearsonate (ABA). Of 576 microwells originally seeded, 132 demonstrated growing cell clones, 4 of which produced an ABA-binding supernatant factor. When tested in vivo for suppression of delayed-type hypersensitivity to ABA, two of these cell lines, A4 and F12, were shown to produce suppressive supernatant factors. Fluorescence analysis of the F12 cells with appropriate antisera demonstrated this T cell hybrid to be Thy 1.2+, Lyt 1+,2-, and surface immunoglobulin negative, the surface marker phenotype of conventional ABA-specific suppressor T cells. This cloned suppressor cell line, F12, produces a culture supernatant factor that is suppressive at dilutions up to 1:100 and has provided material for genetic and immunochemical analysis.
Expression of major histocompatibility antigens on pancreatic islet cells.
Authors: Baekkeskov S , Kanatsuna T , Klareskog L , Nielsen D A , Peterson P A , Rubenstein A H , Steiner D F , Lernmark A
Published: May 2006

Insulin-dependent diabetes mellitus is often accompanied by manifestations of autoimmunity and is frequently associated with certain HLA haplotypes, predominantly DR3 and DR4. Because the major histocompatibility antigens are important determinants of the immune response in various tissues, we have investigated their expression on the pancreatic islet cells. Human, mouse, or rat islets of Langerhans, as well as lymphocytes or other differentiated cells, were biosynthetically labeled with radioactive amino acids, lysed in detergent, and immunoprecipitated with several antisera specific for major histocompatibility antigenic groups. The immunoprecipitates were analyzed by NaDodSo4/polyacrylamide gel electrophoresis under reducing conditions followed by autoradiography. The major histocompatibility antigens corresponding to the H-2 K,D molecules in mice, the H1-A in rats, and the HLA-A, -B, and -C in humans were precipitated from both islet and lymphocyte lysates and were accompanied by beta 2-microglobulin. Binding of H-2 antibodies to islet cells was also confirmed by a radioligand assay using 125I-labeled protein A and by indirect immunofluorescence. Analyses in the fluorescence-activated cell sorter revealed that greater than 95% of the cells in the beta-cell-rich fraction were fluorescent, providing further evidence that the pancreatic beta cells express the major histocompatibility antigens. Monoclonal antibodies or mouse alloantisera against HLA-DR or Ia antigens did not react with labeled pancreatic islet cell proteins.
Gas-phase pyrolytic formation and dimerization of benzocyclobutenes: Synthesis of [2
4
](1,2,4,5) cyclophane
Authors: Eaton Bruce E. , Laganis E. D. , Boekelheide V.
Published: May 2006

Gas-phase pyrolysis of benzocyclobutenes in a nitrogen stream at 450°C is a convenient efficient method for preparing dibenzocyclooctadienes. Application of this method to benzo[1,2;4,5]dicyclobutene gives [2
4
](1,2,4,5)cyclophane directly. However, under the same reaction conditions, 3,6-dimethylbenzo[1,2;4,5]dicyclobutene gives the open [2.2]orthocyclophane derivative, whose structure has been established by x-ray crystallographic analysis of the corresponding iron complex.
Uniqueness of solutions of semilinear Poisson equations
Authors: McLeod Kevin , Serrin James
Published: May 2006

Let R

n

denote
n
-dimensional Euclidean space, with
n
> 1. We study the uniqueness of positive solutions
u
(
x
),
x
∈ R

n

, of the semilinear Poisson equation Δ
u
+
f
(
u
) = 0 under the assumption that
u
(
x
) → 0 as ǀxǀ → ∞. This type of problem arises in phase transition theory, in population genetics, and in the theory of nucleon cores, with various different forms of the driving term
f
(
u
). For the important model case
f
(
u
) = −
u
+
u

p

, where
p
is a constant greater than 1, our results show (
i
) that when the dimension
n
of the underlying space is 2, there is at most one solution (up to translation) for any given
p
and (
ii
) that when the dimension
n
is 3, there is at most one solution when 1 <
p
≤ 3. In both cases, the solution is radially symmetric and monotonically decreasing as one moves outward from the center. For dimensions other than 2 or 3, and indeed for the analogous cases of a real dimensional parameter
n
> 1, we obtain corresponding results. We note finally, again for the model case, that existence holds for 1 <
p
< (
n
+ 2)/(
n
− 2); thus, there remains an interesting difference between the parameter ranges for which existence and uniqueness are established.
Isolation and characterization of the intestinal peptide porcine PHI (PHI-27), a new member of the glucagon--secretin family.
Authors: Tatemoto K , Mutt V
Published: May 2006

A new peptide, designated PHI (PHI-27), has been discovered and isolated from porcine upper intestinal tissue by using a chemical method for finding peptide hormones and other active peptides. The method is based on chemical detection of peptides having the cOOH-terminal alpha-amide structure, which is an unusual chemical feature of some peptide hormones and active peptides. Porcine PHI was found in the intestinal extract by the presence of its COOH-terminal isoleucine amide structure. It consists of 27 amino acid residues and has the following amino acid sequence: His-Ala-Asp-Gly-Val-Phe-Thr-Ser-Asp-Phe-Ser-Arg-Leu-Leu-Gly-Gln-Leu-Ser-Ala-Lys -Lys-Tyr-Leu-Glu-Ser-Leu-Ile-NH2. The remarkable sequence homology of PHI to the vasoactive intestinal peptide, secretin, glucagon, and gastric inhibitory polypeptide indicates that this peptide is a member of the glucagon-secretin family. Several biological activities of PHI, similar to those of vasoactive intestinal peptide and secretin, have been reported.
Fate of viral DNA in nonpermissive cells infected with simian virus 40.
Authors: Chia W , Rigby P W
Published: May 2006

Mouse cells are nonpermissive for simian virus 40 (SV40); replication of viral DNA is undetectable and progeny virions are not produced. Infection leads instead to the establishment of stably transformed cell lines in which viral DNA is covalently integrated into cellular DNA. We have followed the fate of SV40 DNA in infected mouse cells to define steps in viral DNA metabolism that precede integration. A novel high molecular weight form of SV40 DNA is synthesized shortly after infection by a process sensitive to the inhibition of DNA replication. This DNA represents polymers in which viral genomes are organized as tandem "head-to-tail" arrays. Recombination can be demonstrated with mutant viruses, but the recombination frequency is not high enough to account for the synthesis of polymers by recombination between infecting genomes. We conclude that polymers are synthesized by DNA replication and that they then recombine with one another. We believe that the polymers also recombine with cellular DNA and are thus the precursor to integrated viral DNA. Such a model accounts directly for the high frequency of tandemly duplicated viral insertions in transformed cells and also leads to experimentally testable predictions.
mRNAs for the immobilization antigens of
Paramecium
Authors: Preer John R. , Preer Louise B. , Rudman Bertina M.
Published: May 2006

Immobilization antigens of stock 51 of
Paramecium tetraurelia
were subjected to electrophoresis in NaDodSO
4
/polyacrylamide gels. Type A is estimated to have a molecular size of 300,000 daltons; H is estimated to be 288,000, D to be 280,000, E to be 270,000, B to be 253,000, and C to be 250,000. Poly(A)
+
RNAs have been isolated from cells producing these antigens and subjected to electrophoresis in methylmercury gels. A major band is found to vary in mobility with antigenic type: Its position in preparations derived from paramecia synthesizing antigen A indicates a size of 8400 nucleotide residues; its position from paramecia synthesizing other antigens indicate H, 8200; D, 7900; E, 7500; B, 7600; and C, 7000. Because of the sizes and quantities of these RNAs, it is argued that they probably represent the mRNAs for the immobilization antigens. It is concluded that each immobilization antigen probably consists of a single polypeptide and that only one major serotype-determining mRNA is present in each antigenically different paramecium.
Clonal analysis of early and late stages of erythroleukemia induced by molecular clones of integrated spleen focus-forming virus.
Authors: Yamamoto Y , Gamble C L , Clark S P , Joyner A , Shibuya T , MacDonald M E , Mager D , Bernstein A , Mak T W
Published: May 2006

The integrated proviral DNA of the polycythemia-inducing isolate of Friend spleen focus-forming virus (SFFVp) has been identified in rat cell clones nonproductively infected with this replication-defective erythroleukemia virus and cloned in phage lambda vectors. These lambda SFFVp recombinants, lambda SFFVp502 and lambda SFFVp542, contain endonuclease EcoRI inserts of size 7.4 and 8.2 kilobases, respectively, and include full copies of the SFFVp genome, along with host flanking sequences. Infectivity of the cloned SFFVp genomes was tested by a two-step DNA transfer procedure involving transfection of the cloned DNA into 3T3 mouse fibroblasts or cotransfer of the cloned DNA into thymidine kinase-deficient 3T3 cells together with the cloned thymidine kinase gene of herpes simplex virus, followed by rescue of the transferred DNA by superinfection with a helper virus. Inoculation of the rescued virus into adult mice resulted in the appearance of spleen foci, rapid splenomegaly, and polycythemia. Early after infection, spleen cell populations contained large numbers of cells capable of forming small erythroid colonies in vitro (CFU-E) in the absence of erythropoietin. Late after infection, these mice contained cells capable of forming macroscopic colonies (CFU-FV) in vitro. These data indicate that molecular clones of SFFVp, in conjunction with a helper virus, induce the appearance of hemopoietic colony-forming cells characteristic of both the early and late stages of Friend leukemia.
Epibolin: a protein of human plasma that supports epithelial cell movement.
Authors: Stenn K S
Published: May 2006

Earlier studies suggested that there is a specific activity in mammalian serum and plasma that supports epidermal (epithelial) cell movement. This activity was shown to be nondialyzable and heat labile. In the studies reported here, using standard biochemical procedures--i.e., ammonium sulfate fractionation, ion-exchange and gel filtration chromatography, isoelectric precipitation, and preparative polyacrylamide gel electrophoresis--we have purified a factor from human plasma that supports epidermal cell movement. The factor travels as an apparent single band on disc gel electrophoresis and corresponds to a glycosylated single-chain protein of approximately 65,000 +/- 3,000 daltons. The purified fraction is necessary and sufficient for dissociated epidermal cells, (ii) outgrowth of epithelial sheets from skin explants, and (iii) epiboly, epithelial sheet movement over a floating skin explant. The purified fraction is active at a concentration of 1-2 micrograms/ml of growth medium. It is destroyed by trypsin and its activity is augmented more than 10-fold by a second, as yet unpurified, fraction of plasma. These studies support the notion that a single protein of plasma supports epidermal cell movement and that this protein may play an important role in wound closure. Because it supports epiboly, the most biologically relevant of the assays, it has been named epibolin.
Increasing metastatic potential is associated with increasing genetic instability of clones isolated from murine neoplasms.
Authors: Cifone M A , Fidler I J
Published: May 2006

The metastatic stability of clones, which were derived from the murine UV-2237 fibrosarcoma and which exhibit low or high metastatic potential, was examined after 60-72 days of continuous growth in vitro and in vivo. Subclones of the high metastatic clone exhibited a 140-fold variation in the production of experimental pulmonary metastases after intravenous injection into syngeneic C3H- mice. In contrast, subclones from the low metastatic clone varied only slightly (8-fold). Using cloned cells from three mouse tumors with differing metastatic potential, we determined the spontaneous mutation rates of cells with low or high metastatic capacities with respect to the selective genetic markers, 6-thiopurine resistance or ouabain resistance, or both. In all cases, cells with high metastatic potential had a 3- to 7-fold increase in the rate of mutation (per cell generation) at both genetic loci, as compared with their low metastatic but tumorigenic cell controls. These results support the hypothesis that the evolution of tumors from the benign to the malignant state could be the consequence of acquired genetic instability in the neoplastic cells.
Morphometric aspects of ciliary distribution and ciliogenesis in human nasal epithelium.
Authors: Carson J L , Collier A M , Knowles M R , Boucher R C , Rose J G
Published: May 2006

Observations of freeze-fracture preparations of human nasal epithelium have provided a unique perspective of the spatial distribution of epithelial cell cilia unattainable by more conventional ultrastructural techniques. The initial stages of ciliogenesis were characterized ultrastructurally in these preparations by differentiation of the lumenal aspect of the epithelial cell membrane prior to the emergence and maturation of new cilia. Morphometric analyses of the resultant electron micrographs indicate that the development of an optimal ciliary population during differentiation of ciliated cells may be integral to the adequate functioning of respiratory mucociliary mechanisms. The frequency with which such ciliogenic structures are observed indicates that ciliogenesis is a common feature of the nasal epithelium and suggests that epithelial cell turnover in the nasal cavities is relatively rapid.
RNA splicing mutation in an aberrantly rearranged immunoglobulin lambda I gene.
Authors: Hozumi N , Wu G E , Murialdo H , Roberts L , Vetter D , Fife W L , Whiteley M , Sadowski P
Published: May 2006

The mouse cell line MOPC 315 is an IgA (lambda II)-producing myeloma. We have studied a derivative of MOPC 315 that secretes normal lambda II chains but no heavy chain. This derivative, MOPC 315-26, was found to contain a rearranged lambda I gene in addition to a rearranged lambda II gene. The rearranged lambda I gene was cloned into bacteriophage lambda DNA and its structure was studied. The lambda I gene was found to have arisen by an aberrant recombination event that resulted in a single base insertion at the site of V-J region joining. In addition, the gene contained numerous point mutations in the vicinity of the junction of the V and J regions. Two point mutations occurred in the donor splice sequence normally used for the removal of the intron between the J and C regions, suggesting that the RNA synthesized from the aberrantly rearranged lambda I gene would be unable to undergo proper RNA splicing.
Integration, transcription, and control of a Drosophila heat shock gene in mouse cells.
Authors: Corces V , Pellicer A , Axel R , Meselson M
Published: May 2006

Mouse L cells were transformed with a cloned 3.6-kilobase (kb) segment of Drosophila melanogaster DNA carrying the 2.25-kb transcribed sequence for the Drosophila 70,000-dalton heat shock protein (hsp70) and 1.1 kb and 0.2 kb of 5' and 3' flanking DNA, respectively. Heat shock of one of three such transformed cell lines containing multiple copies of the intact Drosophila segment induced the abundant accumulation of transcripts of the Drosophila gene, with correct or nearly correct 5' and 3' termini. This provides evidence, in accord with earlier indications, that diverse eukaryotes, including vertebrates, have heat shock systems similar to that studied extensively in Drosophila. Our results suggest that the signals for heat shock transcription and the chromosomal sites with which they interact have been highly conserved in evolution and that the regulatory sequences controlling transcription of the gene for hsp70 lie within the 3.6-kb Drosophila segment.
Serotonin receptor-mediated stimulation of bovine smooth muscle cell prostacyclin synthesis and its modulation by platelet-derived growth factor.
Authors: Coughlin S R , Moskowitz M A , Antoniades H N , Levine L
Published: May 2006

Serotonin (5-hydroxytryptamine; 0.5 microM and above) stimulated the synthesis of prostacyclin (as measured by radioimmunoassay of 6-ketoprostaglandin F1 alpha) by bovine aortic smooth muscle cells in culture. This effect was structurally specific; a similar response was not elicited by the other indoles (tryptophan, n-acetylserotonin, 5-hydroxytryptophan, melatonin, or 5-hydroxyindoleacetic acid) or by the amines phenylephrine, isoproterenol, dopamine, or histamine). The response was reversible and was saturable at serotonin concentrations of 10 microM or higher. An increase in prostacyclin synthesis was elicited by the addition of a serotonin agonist, quipazine (1 microM and above), and antagonized by the serotonin receptor blockers cyproheptadine, methysergide, or methiothepin but not by other aminergic receptor-blocking drugs (e.g., phentolamine or propranolol). This effect was selective for cell type because serotonin or quipazine (100 microM) did not increase prostacyclin synthesis by bovine aortic endothelial cells. The addition of platelet-derived growth factor (PDGF) to cultures of smooth muscle cells dramatically enhanced prostacyclin synthesis in response to the coadministration of serotonin. PDGF greatly increased the maximum response to serotonin without altering the half-maximal effective concentration for serotonin. This synergistic interaction was blocked by the addition of a serotonin-receptor blocking agent. Taken together, these data suggest that serotonin stimulates smooth muscle prostacyclin synthesis through a specific receptor-mediated mechanism that can be modulated by PDGF.
Transfer activity coefficients between water and methanol of complexes of some univalent and barium ions with dibenzocryptand 2.2.2, cryptand 2.2.2, and 18-crown-6
Authors: Chantooni Miran K. , Kolthoff Izaak M.
Published: May 2006

Stability constants,
K
f
LM
n+
(in which L = ligand and M
n+
= metal ion), of complexes of sodium, potassium, silver, thallium(I), and barium with dibenzocryptand 2.2.2 were determined at 25°C in water and methanol. Also determined were transfer activity coefficients between methanol and water of two ligands, dibenzocryptand 2.2.2 and 18-crown-6. From these data, transfer activity coefficients of complexes of these two ligands with the above cations have been calculated. For univalent ion complexes of these ligands and, in addition, for such complexes of dibenzo-18-crown-6 and cryptand 2.2.2, the logarithms of the transfer activity coefficients are of the order of 2.5 units more positive than those of the ligands. Even though methanol is a good hydrogen bond donor, as is water, it is concluded that in methanol only the first solvation layer is built around an ether oxygen of the uncomplexed ligand as compared with several hydration layers in water. Hydrogen bonding to these ether oxygens when these ligands are complexed is greatly decreased as a result of ionic M
n+
-O bonding. Transfer activity coefficients of the barium complexes are found to be the same as those of the ligands. This is attributed to extensive solvation of LBa
2+
.
beta-Endorphin: demonstration of a tertiary structure in aqueous solution.
Authors: Nicolas P , Bewley T A , Gráf L , Li C H
Published: May 2006

Difference spectra generated during thermolysin digestion of camel beta-endorphin at pH 8.2 or at pH 6.5 indicate rapid blue shifting of the near-UV absorption bands of the NH2-terminal tyrosine. A similar spectral change is not observed for the NH2-terminal tyrosine in [Met]enkephalin when it is digested under similar conditions. These results suggest that enzymatic digestion destroys or alters some structural interaction between the NH2-terminal tyrosyl residue of the endorphin and a residue(s) within the COOH-terminal segment of the molecule. Peptide mapping of the digest as a function of time suggests that cleavage of the bond linking the alanine-21 and isoleucine-22 residues produces most of the observed effect. These data provide evidence for the existence of a tertiary structure for beta-endorphin in aqueous solutions.
Ultrastructural identification of extension aminopropeptides of type I and III collagens in human skin.
Authors: Fleischmajer R , Timpl R , Tuderman L , Raisher L , Wiestner M , Perlish J S , Graves P N
Published: May 2006

Human skin was labeled with purified antibodies against type II and III collagens and against their extension aminopropeptides by using the ferritin technique. Both aminopropeptides were visualized mainly along thin collagenous fibrils (diameter, 20-40 nm) and rarely in nonfibrillar regions of the skin. The labeling showed a periodicity of 60-65 nm resembling the D (67 nm) stagger of collagen molecules. Blocking of antibodies with aminopropeptides and treatment of tissues with procollagen NH2-terminal protease abolished labeling. Antibodies against type I collagen uniformly labeled approximately equal to 80% of the fibrils (diameter, 20-80 nm), while reaction with antibodies against type III collagen was restricted to thin fibrils. It is currently thought that the aminopropeptides of procollagen molecules are cleaved after they are released from the cell and before fibril formation. Our data indicate that aminopropeptides are removed at the fibrillar level and that fibril growth can be regulated by extracellular procollagen processing.
Resonance Raman study of the primary photochemistry of bacteriorhodopsin.
Authors: Pande J , Callender R H , Ebrey T G
Published: May 2006

Resonance Raman multicomponent spectra of the light-adapted form of bacteriorhodopsin, bRLA568, and its first photoproduct, K628, have been obtained at liquid nitrogen temperatures. The spectra of both bRLA568 and K628 could be obtained with the known sample compositions under our irradiating conditions and computer subtraction techniques. In agreement with previous results, we find that both bRLA568 and K628 contain chromophores linked to the apoprotein by protonated Schiff bases of retinal. Neither pigment form, suspended in H2O or 2H2O, compares closely to the spectral features of all-trans and 13-cis protonated and deuterated model chromophores, respectively. The data are consistent with other results, suggesting that a chromophore isomerization takes place in the bRLA568-to-K628 phototransition. However, the exact structure of the in situ chromophore would appear not to involve simple trans-to-13-cis structures found in solution.
Nucleotide insertion in the anticodon loop of a glycine transfer RNA causes missense suppression.
Authors: Prather N E , Murgola E J , Mims B H
Published: May 2006

We have determined the nucleotide sequences of two unusual UGG-suppressing glycine tRNAs from Escherichia coli and, as a result, have discovered a new mechanism for the generation of missense suppressors. The suppressor tRNAs translate UGG but not UGA. Each arose as a consequence of spontaneous mutational alteration of glyT, the gene for the GGA/G-reading glycine tRNA of E. coli. In each mutant tRNA, the change in primary structure involved the insertion of an adenylate residue on the 3' side of the anticodon and the loss of a modification of the uridylate residue at the 5' end of the anticodon. A "shift" of the effective anticodon by one nucleotide in the 3' direction can account for the new coding specificity of these tRNAs.
Original domain for the serum albumin family arose from repeated sequences.
Authors: Ohno S
Published: May 2006

The characteristic three-domain structure has been conserved throughout mammalian evolution by serum albumin and its fetal counterpart, alpha-fetoprotein. Thus, one still detects 35.2% amino acid sequence homology between bovine serum albumin and murine alpha-fetoprotein. Yet, natural selection cannot be invoked as the major factor responsible for the observed conservation of these sequences, for the simple reason of their dispensability. Inherited analbuminemia is apparently a harmless trait in man and the rat. The conservation appears inherent in their repetitious origin. Each protein is made of triplicate copies of the ancestral domain. Furthermore, analysis of the published sequence data suggests that the original coding sequence for the ancestral domain arose as repeats of the 18-base-long primordial building block sequence TTC-ACA-GAG-GAG-CAG-CTG specifying Phe-Thr-Glu-Glu-Gln-Leu and its shorter subsidiary TTC-ATG-GAG-GAG specifying Phe-Met-Glu-Glu. Consequently, the homology between bovine serum albumin and alpha-fetoprotein is mostly confined to small segments still specified by recognizable descendants of these building block sequences. The point to be made here is that evolutionary conservation of coding sequences can be an inherent property; natural selection need not be invoked.
Neonatal tolerance to alloantigens alters major histocompatibility complex-restricted response patterns.
Authors: Müllbacher A
Published: May 2006

Male-specific transplantation antigen (H-Y)-immune cytotoxic T cells of some individual CBA/H mice exhibit lytic activity on male and female allogeneic targets (e.g., H-2b). Neonatal tolerance to H-2b abrogates the ability of CBA mice to generate secondary H-Y-immune cytotoxic T cells, but such cell activity to third-party alloantigens and to Bebaru and influenza virus is not impaired. The results are discussed in relationship to dominant major histocompatibility complex-coded immune response gene effects on cytotoxic T-cell responses.
Radioimmunoassay of the leukotrienes of slow reacting substance of anaphylaxis.
Authors: Levine L , Morgan R A , Lewis R A , Austen K F , Clark D A , Marfat A , Corey E J
Published: May 2006

A rabbit immunized with a conjugate of leukotriene D4 (LTD4) and bovine albumin via the icosanoid carboxyl produced antibodies with comparable affinities for leukotrienes C4, D4, and E4 (LTC4, LTD4, and LTE4) and their 11-trans stereoisomers. The antibodies bound 3H-labeled 11-trans-LTC4 and 11-trans-LTC4 with the same average association constant (Ka) of 2.8 x 10(9) M-1 at 37 degrees C and were present at a concentration of 0.32 microgram/ml of the immune rabbit plasma. When 9.5 microliter of anti-LTD4 and 108 pmol of 11-trans-[3H]LTC4 (40 Ci/mmol) were incubated in a volume of 300 microliter with LTC4, LTD4, LTE4, or their 11-trans stereoisomers, 50% inhibition of 11-trans-[3H]LTC4 binding was achieved at levels varying between 0.3 and 0.7 ng. As assessed with synthetic analogs of the natural leukotrienes, the antibodies recognized neither those changes within the 6-sulfidopeptide unit of LTD4 produced by deamination or modest peptide lengthening nor the specific stereochemistry of the delta 14-cis double bond. However, the antibodies did recognize the triene lipid domain and the position and spatial orientation of the glutathione or cysteinylglycine function. Binding of 11-trans-[3H]LTC4 by anti-LTD4 was not inhibited by glutathione, cystinylbisglycine, arachidonic acid, or 5-hydroxy-6,8,11,14-icosatetraenoic acid, and leukotriene B4 (LTB4) was about 1/1000th as active as LTC4, LTD4, or LTE4. Mouse lymphoma (WEHI-5) and rat basophil leukemia (RBL-1) cells, when stimulated with calcium ionophore A23187, each produced immunoreactive leukotrienes; and LTC4, LTD4, and LTE4 from RBL-1 cells were individually quantitated by radioimmunoassay after resolution by high-performance liquid chromatography.
Two growth factors and two hormones regulate initiation of DNA synthesis in cultured mouse cells through different pathways of events.
Authors: Jimenez de Asua L , Richmond K M , Otto A M
Published: May 2006

Epidermal growth factor (EGF) as well as prostaglandin F2 alpha (PGF2 alpha), when added to quiescent, confluent Swiss 3T3 cells, stimulate the initiation of DNA synthesis, which occurs with apparent first-order kinetics after a lag phase of 14-15 hr. These two growth factors appear to stimulate similar events; insulin enhances and hydrocortisone can inhibit the stimulatory effect of either. Here we show that the addition of EGF and PGF2 alpha together, however, results in a synergistic effect seen at the end of the lag phase, but only when EGF and PGF2 alpha are added within 6 hr of each other. Addition of one growth factor 10 or 15 hr after the other delayed the synergy for 15 hr after the addition of the second growth factor. Insulin further increased the rate of entry into the s phage stimulated by EGF and PGF2 alpha together, whereas hydrocortisone inhibited the stimulatory effect observed with either EGF or PGF2 alpha alone. These results suggest that, in spite of the common events responsible for the interactions with the two hormones, EGF and PGF2 alpha must have differences in their sequences of events that initiate DNA synthesis.