bluuebunny/crossref_metadata_2025 huggingface dataset:
Direct selection
in vitro
for herbicide-resistant mutants of
Nicotiana tabacum
Authors: Chaleff R. S. , Parsons M. F.
Published: May 2006

Seven cell lines of
Nicotiana tabacum
resistant to the herbicide picloram were isolated from cell cultures. In crosses of plants regenerated from four cell lines, resistance was inherited as a single dominant Mendelian allele. Plants could not be regenerated from one cell line, and expression of resistance proved unstable in two others.
Lymphoid dendritic cells are potent stimulators of the primary mixed leukocyte reaction in mice.
Authors: Steinman R M , Witmer M D
Published: May 2006

Dendrite cells (DCs) are a new cell type initially identified in mouse lymphoid organs. Recently, DCs have been purified from mouse spleen. This paper demonstrates a functional role of DCs: they are potent stimulators of the primary mixed leukocytes reaction (MLR). As few as 300-1000 DCs doubled the proliferative activity of 5 X 10(6) allogeneic responder spleen cells, while 0.3-1.0 X 10(5) DCs induced a maximal stimulation of 30- to 80-fold. Between these extremes, the log of the MLR response increased linearly with the log of DC numbers. This dose-response assay was then used to compare the potency of purified DCs with that of other heterogeneous lymphoid populations, many of which gave dose-response curves with similar slopes. The potency of purified DCs as MLR stimulators was 100-300 times greater than that of unfractionated spleen cells. When spleen cells were fractionated by simple physical techniques, MLR-stimulating capacity in the subpopulations correlated closely with DC numbers. Removal of splenic B or T lymphocytes, by anti-immunoglobulin or anti-brain serum plus complement, did not reduce MLR-stimulating capacity. Finally, several populations, enriched in mononuclear phagocytes but lacking in DCs, stimulated weakly if at all. We conclude that DCs are a potent stimulating cell and are at least 100 times more effective than other major cell subclasses--i.e., B and T lymphocytes and macrophages.
Induction of neurite outgrowth by a conditioned-medium factor bound to the culture substratum
Authors: Collins Frank
Published: May 2006

Heart-cell conditioned medium (HCM) induces rapid neurite outgrowth from isolated neurons in culture. The following evidence indicates that this action of HCM is due to a trypsin-sensitive factor which attaches to the polyornithinecoated culture substratum: (
i
) Pretreatment of the culture substratum with HCM allows rapid neurite outgrowth to occur even in unconditioned media. The active factor remains bound to the substratum during the period of neurite outgrowth. (
ii
) The substratum-bound activity is destroyed by trypsin treatment, but is insensitive to collagenase, RNase, and DNase. (
iii
) The factor that binds to the substratum is essential for neurite outgrowth, because HCM is no longer active when the material that binds to the polyornithine substratum has been removed by passage of the HCM over a series of culture dishes. However, this “depleted” HCM is still able to support the growth of nonneuronal cells. (
iv
) Most significantly, when neurons are cultured in whole HCM, the extent of neurite outgrowth is proportional to the amount of substratum-bound activity and not to the amount in solution, indicating that the substratum-bound form of the factor is more active. Previous observations [Collins, F. (1978)
Dev. Biol.
65, 50-57] suggest that HCM promotes neurite outgrowth by increasing the adhesion between nerve cell surface extensions and the polyornithine-coated culture substratum. It is possible, therefore, that the factor in HCM that binds to the substratum possesses sites to which nerve cell surface components adhere.
Regeneration of olfactory axons and synapse formation in the forebrain after bulbectomy in neonatal mice.
Authors: Graziadei P P , Levine R R , Graziadei G A
Published: May 2006

We removed the right olfactory bulb in neonatal mice, leaving the bulb on the left side intact as an internal control. At 5 days of survival time, we observed that the right cerebral hemisphere was displaced forward to occupy the region made vacant by removal of the bulb. The frontal cortex was, consequently, in close proximity to the lamina cribrosa. As a result of bulb ablation and severance of the fila olfactoria, the sensory perikarya underwent total retrograde degeneration, which peaked at 8 days. New neurons differentiated in the neuroepithelium from basal stem cells and, at 30 days of survival, mature sensory neurons were reconstituted. These new elements sent their axons through the lamina cribrosa to reach the protruding cerebral hemisphere, penetrating it and forming glomeruli-like structures directly in the host tissue. The "glomerulization" of the sensory fibers persisted and actually expanded between 60 and 120 days. The new glomeruli were organized intimately within the brain tissue, and large neurons of the cortex were observed to be in close proximity. Ultrastructural observations of the newly formed glomeruli demonstrated that typical sensory axon terminals profusely branched and synapsed with unidentified postsynaptic processes that penetrated the glomeruli from the surrounding cerebral tissue.
Interacting enzyme systems at steady state: further Monte Carlo calculations on two-state molecules.
Authors: Hill T L , Chen Y D
Published: May 2006

In this work, Monte Carlo calculations were made on a 10 x 10 lattice of two-state, steady-state enzyme molecules in two special cases for which the Bragg-Williams (mean field) approximation had earlier produced some very interesting phase-transition properties. The Monte Carlo results proved to be similar to Bragg-Williams in some respects but not in others. The discrepancies are attributed primarily to; (i) inadequate treatment by Bragg-Williams of strong negative cooperativity; and (ii) the finite size of the 10 x 10 lattice used in the exact calculations.
Photodestruction of pheomelanin: role of oxygen.
Authors: Chedekel M R , Smith S K , Post P W , Pokora A , Vessell D L
Published: May 2006

Pheomelanin, the red-brown polymeric pigment in the skin and hair of red-headed humans, is composed of a protein fraction covalently bound to a colored chromophore. Photolysis of aerated aqueous phemelanin solutions, isolated from human red hair, results in destruction of the chromophore and liberation of the peptide fraction. The rate of photolysis depends on the pH and the concentration of both pigment and oxygen and is slightly inhibited by the enzyme superoxide dismutase (superoxide:superoxide oxidoreductase EC 1.15.1.1). Pheomelanin photolyzed in the presence of nitroblue tetrazolium results in the formation of a blue diformazan, whether or not oxygen is present. Superoxide dismutase inhibits the aerobic photoreduction of nitroblue tetrazolium whereas, in the absence of oxygen, no inhibition is observed. These experiments strongly suggest the involvement of superoxide in the aerobic photolysis of pheomelanin and point out a possible mechanism for ultraviolet-induced cell damage in redheads.
Induction of DNA synthesis in terminally differentiated myotubes by the activation of the src gene of Rous sarcoma virus.
Authors: Kobayashi N , Kaji A
Published: May 2006

Mononucleated myogenic cells from 11-day-old chicken embryos were infected with tsLA24 or tsNY68, temperature-sensitive transformation mutants of Rous sarcoma virus. The infected mononucleated myogenic cells were incubated at the nonpermissive temperature (41 degrees C) and allowed to develop into multinucleated myotubes. These myotubes have withdrawn from the cell cycle, and no DNA synthesis was observed as long as the cultures were maintained at the nonpermissive temperature. However, when the incubation temperature of these cultures was lowered to the permissive temperature (36 degrees C) for expression of the src gene, DNA synthesis was induced in multinucleated myotubes. For this induction of DNA synthesis, cells infected with tsLA24 had to be incubated at the permissive temperature for at least 50 hr, while the induction of DNA synthesis in cells infected with tsNY68 required less than 20 hr. Induction of DNA synthesis was observed by autoradiography as well as by measuring incorporation of [3H]thymidine into the macromolecule fraction in these myotube cultures. For the maintenance of capacity to induce DNA synthesis, constant presence of the src gene product is necessary, because when the temperature of these cultures was returned to 41 decrees C, the myotubes lost the capacity to induce DNA synthesis. During the process of DNA induction one biochemical marker of muscle (creatine kinase) remained unchanged.
Self-nonself concept for cancer and diseases previously known as “autoimmune” diseases
Authors: Levine Philip
Published: May 2006

The illegitimate glycosphingolipid antigens of the P blood group system and of the Forssman (Fs) tissue antigen in adenocarcinoma which are foreign to the host suggest the self-nonself concept which applies also to numerous other diseases such as rheumatoid arthritis, lupus, gluomerulonephritis, and idiopathic acute hemolytic anemia. In the presence of the glycosphingolipid antigens such as ABO, P, and Fs, the normal serum of the homozygote recessive precursor contains antibodies for the missing antigen(s). The expected antibody to the Fs antigen was present in about 75% of normal men and women. In cancer sera, the incidence of anti-Fs was decreased to about 35-40%. On testing the normal population anti-Fs was present in 90% of the sera in the youngest group, and this value gradually diminished in the older groups; the incidence of the antibody in the 70-year age group was to about 60%. The rate of loss of anti-Fs with increasing years appears to parallel the gradual loss of anti-A and anti-B isoagglutinin titers. This phenomenon may be associated with the gradual diminution of protein synthesis with aging or the continuous accumulation of soluble immune complexes in the serum, or both. It is suggested that the self-nonself concept is also the basis for the pathogenesis of rhematoid arthritis, lupus erythematosus, idiopathic acute hemolytic anemia, and numerous other conditions classified as “autoimmune” diseases. Some of these diseases are induced by viruses or drugs or both. When a virus or drug attaches itself to the membrane of a tissue cell, the self is converted to nonself which, in rheumatoid arthiritis, alters its self Ig to nonself Ig.
Effect of rotational symmetry on colored lattices
Authors: Harker David
Published: May 2006

A colored lattice L

c

has a geometrical lattice L. A subgroup lattice L′ of L and each of its cosets consist of like-colored points, each coset having a different color. The index of L′ in L is given by Δ, the determinant of the matrix (

t
jk

) that converts L into L′. This is the order of the factor group {L/L′}, and is also the number
n
of colors present. The crystal systems—i.e., the combinations of rotational symmetry axes—of L

c

,
L
, and L′ are all the same, but L and L′ may have different centerings; this results in 39 combinations of centerings, called here the 39 symmetry types of colored lattices. These types are tabulated here, together with the special forms taken by (

t
jk

) and the formulas for Δ. In only 7 of the 39 types can the number of colors be arbitrary; in most types certain numbers of colors are impossible.
Nucleotide sequence at the junction between the coding region of the adenovirus 2 hexon messenger RNA and its leader sequence.
Authors: Akusjärvi G , Pettersson U
Published: May 2006

We have determined a 139-base-pair sequence of adenovirus 2 DNA that is located immediately leftwards of the cleavage site for endonuclease Sma I at position 51.1. The established sequence includes the hexon AUG initiator codon, located 75--77 nucleotides leftwards of this cleavage site, and codons for the first 26 amino acids of the hexon polypeptide. By the use of purified hexon mRNA as a template and separated strands of small restriction enzyme fragments as specific primers, the complete 5' noncoding region of the hexon mRNA was synthesized and part of its sequence was determined. The tripartite leader sequence of the hexon mRNA starts 39 nucleotides upstream from the initiator AUG triplet and the total length of the 5' noncoding part of the hexon mRNA was estimated to be 235 nucleotides. The sequence at the junction of the leader sequence permits the formation of secondary structures that may be of importance for the splicing reaction.
Detection of viral sequences of low reiteration frequency by in situ hybridization.
Authors: Brahic M , Haase A T
Published: May 2006

The sensitivity of in situ hybridization has been increased at least 10-fold by hybridizing in cDNA excess, by increasing the diffusion of the cDNA through the cells, by hybridizing at optimum temperature, and by stabilizing hybrids during autoradiography. Saturation of intracellular RNA with [3H]cDNA has been achieved. The assay is quantitative. In situ hybridization has been used to detect and quantitate visna virus RNA in infected cells. By using [3H]cDNA with specific activity of 2 X 10(8) dpm/micrograms and conditions that reduce background to negligible levels, 10--20 copies of viral RNA per cell can be detected and quantitated after 2 days of autoradiographic exposure.
Interaction of bombesin and litorin with specific membrane receptors on pancreatic acinar cells
Authors: Jensen R. T. , Moody T. , Pert C. , Rivier J. E. , Gardner J. D.
Published: May 2006

We have prepared
125
I-labeled [Tyr
4
]bombesin and have examined the kinetics, stoichiometry, and chemical specificity with which the labeled peptide binds to dispersed acini from guinea pig pancreas. Binding of
125
I-labeled [Tyr
4
]-bombesin was saturable, temperature-dependent, and reversible and reflected interaction of the labeled peptide with a single class of binding sites on the plasma membrane of pancreatic acinar cells. Each acinar cell possessed approximately 5000 binding sites, and binding of the tracer to these sites could be inhibited by [Tyr
4
]bombesin [concentration for half-maximal effect (Kd), 2 nM], bombesin (Kd, 4 nM), or litorin (Kd, 40 nM) but not by eledoisin, physalemin, somatostatin, carbachol, atropine, secretin, vasocative intestinal peptide, neurotensin, or bovine pancreatic polypeptide. At high concentrations (>0.1 μM), cholecystokinin and caerulein each caused a small (15-20%) reduction in binding of lableled [Tyr
4
]bombesin. With bombesin, litorin, and [Tyr
4
]bombesin, there was a close correlation between the relative potency for inhibition of binding of labeled [Tyr
4
]bombesin and that for stimulation of amylase secretion. For a given peptide, however, a 10-fold higher concentration was required for half-maximal inhibition of binding than for half-maximal stimulation of amylase secretion, calcium outflux, or cyclic GMP accumulation. These results indicate that dispersed acini from guinea pig pancreas possess a single class of receptors that interact with [Tyr
4
]bombesin, bombesin, and litorin and that occupation of 25% of these receptors will cause a maximal biological response.
Kin selection: A classical approach and a general solution
Authors: Wade Michael J.
Published: May 2006

The necessary conditions for the spread of genes that determine social behaviors and the rate of spread of these genes are derived for a simple model (single locus, two alleles, random mating, discrete generations) by using the classical population genetics approach pioneered by Haldane and the linear fitness function used previously by D. S. Wilson. These results are derived for social behaviors that are manifested by individuals within families, within pairs of families, or within groups of
k
families, for both diploid and haplodiploid organisms. I show that, when the groups of socially interacting individuals consist of the members of more than one family, severe restrictions are placed on the evolution of altruistic and social behaviors. Specifically, in these instances, the necessary conditions for the evolution of social behaviors are more stringent and the rate of evolution is greatly reduced.
Argininosuccinic aciduria: assignment of the argininosuccinate lyase gene to the pter to q22 region of human chromosome 7 by bioautography.
Authors: Naylor S L , Klebe R J , Shows T B
Published: May 2006

Argininosuccinic aciduria, an autosomal recessive disorder of the urea cycle in humans, is associated with a deficiency of argininosuccinate lyase (ASL; L-argininosuccinate arginine-lyase, EC 4.3.2.1). ASL activity was visualized on gels after electrophoresis by a new method, termed bioautography. Bioautography involves the use of mutant bacteria to visualize the location of mammalian enzymes after zone electrophoresis. By this technique, human ASL migrated to a position different from mouse ASL, while a survey of mouse strains, tissues, and tissue culture cell extracts demonstrated the same electrophoretic form and no genetic variants of mouse ASL. Identifying human ASL, by bioautography in human-mouse somatic cell hybrids has made it possible to regionally locate the ASL gene on human chromosome 7. The human ASL phenotype segregated concordantly with the human enzyme beta-glucoronidase (GUS; beta-D-glucoronide glucuronosohydrolase, EC 3.2.1.31) in cell hybrids, but showed discordant segregation with 32 other enzyme markers representing 23 linkage groups. The gene for GUS has been assigned to chromosome 7 in humans, and cosegregation (synteny) of ASL and GUS demonstrates the assignment of ASL to chromosome 7. Regional location of ASL and GUS to the pter to q22 region of chromosome 7 was achieved in hybrids segregating a 7/9 translocation.
Comparison of cloned mouse alpha- and beta-globin genes: conservation of intervening sequence locations and extragenic homology.
Authors: Leder A , Miller H I , Hamer D H , Seidman J G , Norman B , Sullivan M , Leder P
Published: May 2006

We have cloned and characterized a 9.7-kilobase EcoRI fragment of mouse DNA that contains an alpha-globin gene. The gene is encoded in at least three discontinous segments of DNA interrupted by two small intervening sequences that can be visualized as R-loop structures in the electron miscroscope. The size of the gene and its small intervening sequences fits well with the known size of the alpha-globin mRNA precursor, suggesting that these intervening sequences, like those of beta-globin, are transcribed. Partial sequence analysis indicates that the larger intervening sequence interrupts the alpha-globin gene at a site exactly corresponding to that interrupted by the larger intervening sequences in both the beta-globin major and minor genes. This observation suggests that these sequences were present when the alpha- and beta-globin genes diverged in early vertebrate evolution, more than 500 million years ago. Furthermore, though alpha and betamaj genes are encoded on different chromosomes, when their sequences are compared directly by visualization of heteroduplex structures, only one 150- to 200-base-pair segment of homology is recognized. These homologous sequences are located on the 3'-flanking segments of both genes, about 1.5 kilobases from each.
Autoradiographic localization of γ-aminobutyric acid receptors in the rat central nervous system by using [
3
H]muscimol
Authors: Chan-Palay Victoria
Published: May 2006

Muscimol, a structural analogue and potent agonist of γ-aminobutyric acid (GABA), was used in its tritiated form for the autoradiographic localization of GABA receptors in the rat central nervous system. [
3
H]Muscimol ([
3
H]M) was incubated with brain slices or was injected intracortically or into intraocular brain transplants. As indicated by [
3
H]M binding and autoradiographic silver grains, GABA receptors display a laminar distribution over the cerebellar cortex, cerebral cortex, and hippocampus (in order of decreasing quantity); and a nonlaminar distribution in the caudate nucleus and substantia nigra. [
3
H]M binding was not affected by brief prior treatment of brain slices with (-)nipecotic acid or guvacine, two potent inhibitors of GABA uptake, indicating receptor binding specificity. Systemic administration of unlabeled muscimol interferred with binding of [
3
H]M binding subsequently administered
in vitro
, indicating that muscimol or a metabolite of it traverses the blood/brain barrier and binds to receptor sites, possibly in a manner competitive with [
3
H]M. [
3
H]M binding was greatest in the cerebellum. Quantitative analyses of the distribution of autoradiographic silver grains in the cerebellar cortex and dentate nucleus showed a general distribution of GABA receptors in the neuropil: molecular layer > granular layer > cerebellar nuclei > white matter. The highest binding of [
3
H]M occurred on the Purkinje cell somatic surface, in the basket axon formation surrounding the cell body and its axon initial segment, and somewhat less on basket and stellate cell somata. Neuroglial cells of the cortex have no [
3
H]M binding capacity; some glial cells in the cerebellar nuclei do. The role of glial cells in GABA uptake, metabolism, and GABA-receptor-mediated mechanisms remains to be clarified. The distribution of GABA receptors as indicated by [
3
H]M binding differs from the distribution of [
3
H]GABA uptake and GABA synthesizing and degradative sites.
Two regions of the adenovirus 2 genome specify families of late polysomal RNAs containing common sequences.
Authors: McGrogan M , Raskas H J
Published: May 2006

Late cytoplasmic RNAs specified by two regions of the adenovirus 2 genome (39.3--51.8 and 70.7--83.4 map units) were analyzed by size fractionation of poly(A)-[3H]RNA and subsequent hybridization to DNA fragments. Both regions encode RNAs whose sequence content exceeds the coding capacity of the region. These multiple transcripts are likely to function as mRNAs, because they are present on polyribosomes. The DNA segment 39.3--51.8 specifies 27S, 22S, and 18S RNAs. The genome sites specifying these three size classes were determined by hybridizations with seven different DNA fragments from this region of the genome. The 3' termini of all three size classes are specified by sequences near a common site, position 50.1. The 27S RNA includes sequences beginning near 39.3, the 22S RNA contains sequences from 41.0, and the 18S RNA includes sequences from approximately 45.3 on the unit genome. A second family of four RNAs is transcribed from 70.7--83.4. These 28S, 22S, 18S, and 16S RNAs have a relationship similar to the RNAs transcribed from 39.3--51.8. Sequences near the 5' ends of these four size classes are specified by different genome sites. However, the 3' termini of all four size classes were localized near map position 80.4. The synthesis of families of RNA may allow the translation of multiple polypeptides from a genome segment that has only one terminator site for mRNA synthesis.
Conformational changes of the chromatin subunit.
Authors: Gordon V C , Knobler C M , Olins D E , Schumaker V N
Published: May 2006

Hydrodynamic studies on monomer chromatin subunits (v1) as a function of ionic strength (0.7 mM to 100 mM KCl) indicate two salt-dependent conformational transitions. An abrupt transition occurs at about 7.5 mM ionic strength. Decreasing the ionic strength from 10 to 5 mM results in a decrease in s20,w of the v1 from 11.1 to 9.9 S. The diffusion coefficient D20,w decreases from 3.3 to 2.7 X 10(-7) cm2 sec--1. The v1 crosslinked with formaldehyde at 10 mM ionic strength do not undergo a similar salt-dependent change in s20,w. Another transition is observed at about 1 mM ionic strength; s20,w decreases to 9.4 S and D20,w decreases to 2.2 X 10(-7) cm2 sec--1. Throughout the entire salt range the molecular weight of the v1 remains reasonably constant, implying that salt-dependent changes in the frictional coefficient are being observed. Various hydrodynamic models are considered as possible interpretations of the observed changes in the frictional coefficient.
Ionophore A-23187- and thrombin-induced platelet aggregation: independence from cycloxygenase products.
Authors: Lapetina E G , Chandrabose K A , Cuatrecasas P
Published: May 2006

Stimulation of platelets labeled with [14C]-arachidonate by ionophore A23187 or thrombin produces rapid degradation of specific membrane phospholipids. This is also reflected by the release of [14C]archidonate, which is immediately transformed into products of the cycloxygenase and lipoxygenase enzyme systems, and by increased labeling of phosphatidic acid. Arachidonate metabolism can be effectively prevented by preincubation with indomethacin and eicosatetraynoic acid, but platelet aggregation induced by ionophore A23187 or trombin is not blocked under these conditions. Nevertheless, in the virtually total absence of metabolism of arachidonate, platelet aggregation still occurs concomitantly with phospholipid breakdown and with increased labeling of phosphatidic acid. Increased levels of cyclic AMP block both phospholipase activation and aggregation induced by ionophore A23187 and trombin. These data suggest that some early consequence of phospholipase activation, independent of a metabolic product of arachidonate but possibly related to the production of phosphatidic acid, may play a central, causative role in mediating platelet aggregation.
Production a corpus luteum angiogenic factor responsible for proliferation of capillaries and neovascularization of the corpus luteum.
Authors: Gospodarowicz D , Thakral K K
Published: May 2006

Factors controlling the changes in the vascular pattern of the ovary that occur during the reproductive cycle have been investigated. By using the rabbit cornea, the abilities of ovarian corpus luteum and of follicles to induce neovascularization have been compared. While the corpus luteum is capable of inducing neovascularization, the follicles do not have this ability. It is therefore likely that the corpus luteum actively participates in its own neovascularization by secreting a factor that we have called "corpus leutem angiogenic factor" (CLAF).
Regulation of the self-renewal probability in Hydra stem cell clones.
Authors: David C N , MacWilliams H
Published: May 2006

Hydra interstitial stem cells continuously give rise to daughter stem cells as well as precursors for nerve and nematocyte differentiation. Growth of the stem cell population is controlled by the self-renewal probability (Ps): Ps is the fraction of stem cell daughters that remain stem cells in each generation. We have determined Ps for Hydra interstitial stem cells by using a novel technique based on the cell conposition of clones. Stem cell clones were grown in aggregates of nitrogen mustard-inactivated Hydra tissue. They contain several hundred cells after 14 days of growth, including stem cells, differentiating nematocytes, and differentiating nerve cells. Clone size, size variability, and the ratio of differentiating cells to stem cells are sensitive measures of Ps. We have prepared standard curves relating these parameters to Ps, using computer simulations of clone growth. Comparisoon of the experimentally observed parameter of clones to these curves indicates that Ps decreases from 0.8 in 5- to 6-day clones to 0.6 in 10- to 12-day clones. The decrease in Ps coincides with the increase in clone size and suggest that Ps may be regulated by the density of stem cells in clones. Such a mechanism could be responsible for the observed homeostasis of stem cell populations in vivo.
Control of antibody heterogeneity in strain 2 guinea pigs.
Authors: Reese R T , Chase M W , Nagel G P
Published: May 2006

When Wright's strain 2 guinea pigs are immunized with 2,4-dinitrophenyl conjugates in complete Freund's adjuvant, the antibody response varies with the choice of carrier. Immunization with 2,4-dinitrophenyl-guinea pig albumin elicits a response that requires approximately 21 days to detect. The antibody produced is, according to isoelectric focusing, relatively homogeneous IgG2 having a neutral isoelectric point. On small amounts of IgG are produced. Stimulation of animals with 2,4-dinitrophenyl-keyhole Limpet hemocyanin produces a response by 14 days is similar to the peak response inititated by 2,4-dinitrophenyl-guinea pig albumin. With time, however, basic IgG2 populations are added to the response. By days 28-35, when the anti-hapten response has reached a plateau, the major subpopulation of antibody is neutral IgG2, but there exists several times as much basic IgG2 as IgG1. These data suggest that antigen-responsive cells may be ordered into groups having different thresholds of activation. Regardless of the strength of the antigenic stimulus, there is a set sequence of activation. The same cells always play the primary role, contributing most of the antibody regardless of whether secondary clones of cells are activated.
Complete amino acid sequence of the alpha 2 heavy chain of a human IgA2 immunoglobulin of the A2m (2) allotype.
Authors: Toraño A , Putnam F W
Published: May 2006

The complete amino acid sequence of the alpha 2 heavy chain of a human IgA2 immunoglobulin of the A2m(2) allotype has been determined and is compared to the sequence of the alpha 1 chain of the human IgA1 subclass. The characteristic differences between the alpha 1 and alpha 2 chains are greatest in the hinge region and in the location and number of the oligosaccharides. Apart from the duplication in the hinge region of alpha 1 and the deletion in alpha 2, there are 23 amino acid exchanges in the constant (C) regions of the two chains. Accepted mutations are related to the surface accessibility of the residues and the proximity of carbohydrate. The results indicate that human IgA and IgG subclasses arose late in evolution and reflect similar mutationa pressures.
Structure of hemoglobins Zürich [His E7(63)beta replaced by Arg] and Sydney [Val E11(67)beta replaced by Ala] and role of the distal residues in ligand binding.
Authors: Tucker P W , Phillips S E , Perutz M F , Houtchens R , Caughey W S
Published: May 2006

In hemoglobin Zürich the side chain of the distal arginine attaches itself to the propionate of the heme, leaving the heme pocket wide open, allowing sulfanilamides easy access to the iron, and doubling the partition coefficient between CO and O2. The replacement of the distal valine by alanine in hemoglobin Sydney leaves a large gap inside the heme pocket, which is partly filled by a water molecule bonded to the distal histidine. Hemoglobin Sydney has the same partition coefficient between CO and O2 as hemoglobin A.Replacement of the distal histidine increases the stretching frequency of CO linked to the beta heme by 6 cm-1, but replacement of the distal valine increases it by only 3 cm-1, but replacement of the distal histidine leaves the O-O stretching frequency unchanged.
Spliced early mRNAs of simian virus 40
Authors: Berk Arnold J. , Sharp Phillip A.
Published: May 2006

Biochemical methods are presented for determining the structure of spliced RNAs present in cells at low concentrations. Two cytoplasmic spliced viral RNAs were detected in CV-1 cells during the early phase of simian virus 40 (SV40) infection. One is 2200 nucleotides in length and is composed of two parts, 330 and 1900 nucleotides, mapping from ∼0.67 to ∼0.60 and from ∼0.54 to ∼0.14, respectively, on the standard viral map. The other is 2500 nucleotides long and also is composed of two parts, 630 and 1900 nucleotides mapping from ∼0.67 to ∼0.54 and from ∼0.54 to ∼0.14, respectively. Correlation of the structure of these mRNAs with the structure of the early SV40 proteins, small T antigen (17,000 daltons) and large T antigen (90,000 daltons), determined by others suggests that: (
i
) translation of the 2500-nucleotide mRNA yields small T antigen; (
ii
) translation of the 2200-nucleotide mRNA proceeds through the splice point in the RNA to produce large T antigen (and thus large T antigen is encoded in two separate regions of the viral genome); and (
iii
) the DNA sequences between ∼0.67 and ∼0.60 present in both mRNAs are translated in the same reading frame in both mRNAs to yield two separate gene products that have the same NH
2
-terminal sequence. Therefore, expression of the early SV40 genes is partially controlled at the level of splicing of RNAs.
Inactivation and chemical alteration of mating factor α by cells and spheroplasts of yeast
Authors: Maness Patricia F. , Edelman Gerald M.
Published: May 2006

Mating factor α isolated from yeast culture filtrates was radiolabeled by lactoperoxidase-catalyzed iodination, with full retention of biological activity. The
125
I-labeled α factor bound at low levels to cells of both mating types (
a
and α) but not to spheroplasts. Despite the low level of binding, large quantities of α factor activity were lost by incubation with
a
cells and
a
spheroplasts, but not with α or
a
/α diploid cells. The amount of activity removed from the culture medium was much larger than the amount of
125
I-labeled α factor bound to the cells and was correlated with the appearance of radiolabeled derivatives separable by thin-layer chromatography. Upon removal of the cell wall of α and
a
/α cells, the spheroplasts acquired the ability to remove α factor activity from culture medium, to generate derivatives of α factor, and to respond to α factor by a morphological alteration resembling the response of
a
cells. These findings raise the possibility that the specific enzyme capable of altering α factor, possibly a peptidase, is associated with both
a
and α cells but is masked by the α cell wall. This suggestion is consistent with the observation that the α factor activities of G
1
arrest and cell elongation were blocked by preincubation of
a
cells with the protease inhibitor Trasylol.
Thyroid hormones control lysosomal enzyme activities in liver and skeletal muscle
Authors: DeMartino George N. , Goldberg Alfred L.
Published: May 2006

Because protein degradation in liver and skeletal muscle is increased by thyroid hormones and decreased by thyroidectomy; we investigated the influence of thyroid hormones on the level of lysosomal enzymes. Hypophysectomized rats received daily injections of L-thyroxine or L-triiodothyronine. After 3 days of this regimen, homogenates of liver and skeletal muscle showed a 2- to 3-fold increase in the activities of cathepsin D, cathepsin B, and other lysosomal enzymes including leucine aminopeptidase, acid phosphatase, β-galactosidase,
N
-acetylglucosaminidase, and α-mannosidase. In liver, this effect reflected increased enzyme activity in the two subcellular fractions that normally contain lysosomes. Titration of cathepsin D with pepstatin indicated that the increase in this activity resulted from an increase in the number of enzyme molecules. These effects occurred with both pharmacologic (thyrotoxic) and physiologic (growth-promoting) doses of thyroid hormones. Liver and skeletal muscle from thyroidectomized rats had approximately 50% of the normal levels of lysosomal enzyme activities. Under these various conditions, heart and kidney, tissues in which protein degradation does not appear to be influenced by thyroid hormones, showed no significant changes in lysosomal hydrolases. Thus, thyroid hormones regulate proteolytic and other lysosomal enzyme activities in those tissues in which these hormones influence protein degradation. Many characteristic features of hyperthyroidism and hypothyroidism may result from changes in levels of lysosomal enzymes.
Expression of collagen biosynthetic activities in lymphocytic cells.
Authors: Chen-Kiang S , Cardinale G J , Udenfriend S
Published: May 2006

Immunoglobulin-producing Merwin plasma cells, MPC-11, have been found to contain proplyl hydroxylase (prolyl-glycyl-peptide,2-oxoglutarate:oxygen oxidoreductase; EC 1.14.11.2) activity and its crossreacting protein, as well as hydroxyproline and a collagenous protein that could not be classified as type I, II, or III collagen. Friend leukemic cells, on the other hand, contained only prolyl hydroxylase. Thymus-derived (T) lymphocytes and bone-marrow-derived (B) lymphocytes freshly isolated from BALB/c mice expressed low but significant prolyl hydroxylase activity. Upon stimulation with phytohemagglutinin, the enzyme activity in T cells increased 22- to 29-fold. Crossreacting protein was also increased and appeared more stable than the prolyl hydroxylase. The effect of lipopolysaccharide stimulation on B cells uas similar but not as pronounced. Thus, even when not accompanied by other collagen biosynthetic activities, prolyl hydroxylase is present in all cells of hematologic origin.
Chromosomal integration of phage lambda by means of a DNA insertion element.
Authors: MacHattie L A , Shapiro J A
Published: May 2006

Phage lambdacam112, which contains the chloramphenicol resistance transposon Tn9 and has a deletion of attP and the int gene, will lysogenize Escherichia coli K-12. Prophage integration occurs at different chromosomal sites, including lacY and malB, but not at attB. All lambdacam112 prophages are excised from the chromosome after induction but with various efficiencies for different locations. Heteroduplex analysis of lambdaplacZ transducing phages isolated from a lacY::lambdacam112 prophage reveals an insertion sequence 1 (IS1) element at the joint of viral and chromosomal DNA. Two lines of evidence indicate that lambdacam112 encodes an excision activity that recognizes the IS1 element: (i) prophage derepression increases the frequency of excision from lacY to yield lac+ revertants, and (ii) lambdacam112 infection increases reversion of a galT::IS1 mutation about 50-fold. Our results indicate that the IS1 termini of TN9 can replace attP as a site for lambda insertion in the bacterial chromosome and that excision events are catalyzed by an IS1-encoded protein under lambda repressor and N gene control.
Teratocarcinoma cell variants rejected by syngeneic mice: protection of mice immunized with these variants against other variants and against the original malignant cell line.
Authors: Boon T , Van Pel A
Published: May 2006

We reported previously that, by mutagenesis of a malignant teratocarcinoma cell line, it is possible to obtain a number of variant clones that are incapable of forming progressive tumors. Each of these "tum-" variants is rejected in syngeneic mice and stimulates the production of immune memory cells (self-protection). We show here that four different tum- clones confer an immune protection against each other although this cross-protection is invariably weaker than the self-protection. Moreover, mice immunized with living tum- cells are partially protected against the original malignant teratocarcinoma cells, even though the latter cells are incapable of conferring any immune protection when injected after being killed by irradiation. These results indicate that each tum- variant carries at least one specific transplantation antigen that is absent from the original tumor cell line and from most other tum- variants. Other tumor-specific transplantation antigens are probably present on all the tum- variants and also on the malignant teratocarcinoma cell line.
Opposing effects of calcium and barium in vertebrate rod photoreceptors
Authors: Brown Kenneth T. , Flaming Dale G.
Published: May 2006

Intracellular recording in outer segments of red rods of the toad retina showed that increasing Ca
2+
concentration in the perfusate mimicked certain aspects of light adaptation. Light sensitivity was reduced, the amplitude of light responses was reduced, the time course of light responses was altered by shortening the delay to the peak and increasing the decay rate, and the resting membrane potential was generally increased. These results provide further support for the hypothesis that Ca
2+
acts as an internal transmitter that is subject to light-induced release from the rod saccules. The addition of Ba
2+
to the perfusate mimicked dark adaptation by having effects opposite to all those described for Ca
2+
. The Ba
2+
effects were specific, Mg
2+
and Sr
2+
being ineffective in similar or greater concentration. Also, Ba
2+
gave clear effects at concentrations as low as 0.1 mM. It is proposed that Ba
2+
enters the cell and reduces the uptake of Ca
2+
into the rod saccules, because the various effects of Ba
2+
upon light responses all seem explicable from this hypothesis. Ba
2+
also reduced the resting membrane potential, probably by reducing the membrane conductance for K
+
. The demonstrated effects of Ba
2+
indicate an important role for Ba
2+
in analyzing the ionic aspects of transduction in vertebrate photoreceptors. They also suggest a critical physiological role for Ba
2+
in controlling both the resting properties and light-induced responses of vertebrate rods, because barium has been reported to be concentrated in outer and inner segments of cat photoreceptors.
Automorphic
L
-functions of half-integral weight
Authors: Gelbart S. S. , Piatetski-Shapiro I. I.
Published: May 2006

We describe a theory of Whittaker models and
L
-functions for irreducible representations of a metaplectic covering group of
GL
(2). We explain how to use these
L
-functions to establish an arithmetical correspondence between “genuine” cuspidal representations of the metaplectic group and cuspidal representations of
GL
(2). When our ground field is Q, this correspondence generalizes and reformulates recent results of G. Shimura [(1973)
Ann. Math.
97, 440-481]. A crucial role in our theory is played by what we call “exceptional” cusp forms—those that are completely determined by just one Fourier coefficient.
Early events and mechanisms in the induction of bacterial SOS functions: analysis of the phage repressor inactivation process in vivo.
Authors: Smith C L , Oishi M
Published: May 2006

Different inducing agents and treatments produced distinctly different kinetic patterns of inactivation of prophage repressor molecules. The different patterns were related to differences in the initial altered states of DNA that were produced. The timing of appearance of DNA degradation was correlated with the time needed for repressor inactivation. These characteristics suggest that all the inducing treatments lead to the formation of a final predegradative DNA structure(s) (probably involving scissions) that is acted on by specific DNases, including the recBC DNase, to produce the signals for the induction of prophage.
Acetylcholine-receptor-mediated ion flux in electroplax membrane microsacs (vesicles): Change in mechanism produced by asymmetrical distribution of sodium and potassium ions
Authors: Hess George P. , Lipkowitz Stanley , Struve Gary E.
Published: May 2006

The kinetics of acetylcholine-receptor-mediated efflux of inorganic ions from electroplax microsacs of
Electrophorus electricus
in the presence of varying alkali metal ion concentrations on both sides of the membrane have been investigated. The efflux, a monophasic process when the ion distribution is symmetrical (the same concentrations and types of ions on both sides of the membrane), becomes a biphasic process, consisting of a very rapid initial release of ions followed by a slower first-order process, under conditions that resemble the physiological state of the neural membrane (potassium ions inside the microsacs and sodium ions on the outside). The initial phase of the efflux discriminates between calcium and sodium ions and is inhibited by potassium ions in the external solution. The rate constant associated with this phase is at least 40 times larger than the rate constant associated with the slower efflux. Both phases depend on the concentration of acetylcholine or carbamoylcholine, and are inhibited by receptor inhibitors (
d
-tubocurarine and α-bungarotoxin).

A simple model is proposed which relates the kinetics of the flux to ligand-induced conformational changes in the receptor. We also indicate the relationship between the biphasic kinetics of the flux observed in microsacs to “desensitization,” the phenomenon in which, on addition of acetylcholine, the transmembrane voltage of muscle and nerve cells first increases and then decreases to its resting value within a few seconds.
"Two out of three": an alternative method for codon reading.
Authors: Lagerkvist U
Published: May 2006

An alternative method for codon reading, whereby only the first two codon nucleotides are recognized by the anticodon, is discussed and the experimental evidence for this "two of three" reading method is reviewed. Misreading of codons by the "two out of three" method could pose a significant threat to the fidelity of protein synthesis unless the genetic code is organized in such a way as to prevent this method from being used when it might compromise translational fidelity. Inspection of the genetic code shows that it is arranged in such a way that the "two out of three" reading method can be used without translational errors.
Purification of subunits of
Escherichia coli
DNA gyrase and reconstitution of enzymatic activity
Authors: Higgins N. Patrick , Peebles Craig L. , Sugino Akio , Cozzarelli Nicholas R.
Published: May 2006

Extensively purified DNA gyrase from
Escherichia coli
is inhibited by nalidixic acid and by novobiocin. The enzyme is composed of two subunits, A and B, which were purified as separate components. Subunit A is the product of the gene controlling sensitivity to nalidixic acid (
nalA
) because: (
i
) the electrophoretic mobility of subunit A in the presence of sodium dodecyl sulfate is identical to that of the 105,000-dalton
nalA
gene product; (
ii
) mutants that are resistant to nalidixic acid (

nalA
r

) produce a drug-resistant subunit A; and (
iii
) wild-type subunit A confers drug sensitivity to
in vitro
synthesis of ϕX174 DNA directed by

nalA
r

mutants. Subunit B contains a 95,000-dalton polypeptide and is controlled by the gene specifying sensitivity to novobiocin (
cou
) because

cou
r

mutants produce a novobiocin-resistant subunit B and novobiocin-resitant gyrase is made drug sensitive by wild-type subunit B. Subunits A and B associate, so that gyrase was also purified as a complex containing 105,000- and 95,000-dalton polypeptides. This enzyme and gyrase reconstructed from subunits have the same drug sensitivity,
K
m
for ATP, and catalytic properties. The same ratio of subunits gives efficient reconstitution of the reactions intrinsic to DNA gyrase, including catalysis of supercoiling of closed duplex DNA, relaxation of supercoiled DNA in the absence of ATP, and site-specific cleavage of DNA induced by sodium dodecyl sulfate.
Photosynthetic characteristics and organization of chlorophyll in marine dinoflagellates
Authors: Prézelin Barbara B. , Alberte Randall S.
Published: May 2006

The photosystem I reaction center complex, the
P
-700-chlorophyll
a
-protein, has been isolated from the photosynthetic membranes of two marine dinoflagellates,
Gonyaulax polyedra
and
Glenodinium
sp., by detergent solubilization with Triton X-100. The complexes isolated from the two species were indistinguishable, exhibiting identical absorption properties (400-700 nm) at both room (300 K) and low (77 K) temperature. The room temperature, red wavelength maximum was at 675 nm. The absorption properties, kinetics of photobleaching, sodium dodecyl sulfate electrophoretic mobilities, and chlorophyll
a/P
-700 ratio (50 ± 10) of the
P
-700-chlorophyll
a
-protein complexes from the two species also were essentially the same and similar to those properties characterizing
P
-700-chlorophyll
a
-protein complexes of higher plants and green algae.

Photosynthetic unit sizes were determined for cells grown at 1000 μW/cm
2
. Both dinoflagellates had unit sizes (total chlorophyll/
P
-700 ratios) of about 600, even though the distribution of chlorophyll
a
, chlorophyll
c
, and peridinin in the light-harvesting components differed in
Gonyaulax
and
Glenodinium
. The number of photosynthetic units per cell in the two species correlates directly with their photosynthetic activities. A model is presented for the distribution of chlorophyll in the photosynthetic apparatus of these dinoflagellates which accounts for the known role of the isolated pigment-protein complexes and for the known photoadaptive physiology in pigmentation and photosynthesis for these species.