bluuebunny/crossref_metadata_2025 huggingface dataset:
Generation of “bastard” molecular ions from van der Waals clusters: Ar

n

(C
2
Cl
4
)

m

+
ions, suspected interlopers in collection of solar neutrinos
Authors: Buelow S. J. , Worsnop D. R. , Herschbach D. R.
Published: May 2006

Gaseous molecular ions containing argon and perchlorethylene, Ar

n

(C
2
Cl
4
)

m

+
in which
n
≥ 1-29 and
m
≥ 1-4, are produced by electron bombardment of van der Waals clusters formed by expanding an Ar/C
2
Cl
4
mixture through a supersonic nozzle. Previous attempts to observe such ions in a high-pressure mass spectrometer were not successful, as with many other (“bastard”) ions that similarly lack a stable chemically bound neutral parent molecule. This is probably due to dissociation induced by the large exoergicity from charge transfer between species that differ greatly in ionization potential. Use of van der Waals clusters as parent species avoids entirely the exoergicity problem and thus offers a general method to generate bastard ions. The Ar(C
2
Cl
4
)

m

+
ions have been suspected of interfering with collection of
37
Ar
+
ions produced by the
37
Cl(
v
,e
-
)
37
Ar
+
reaction in the solar neutrino observatory. Although, as shown by our results, these ions are stable, they are unlikely to inhibit collection on the long time scale of the solar neutrino experiment.
Yeast 2-micrometer plasmid DNA replication in vitro: origin and direction.
Authors: Kojo H , Greenberg B D , Sugino A
Published: May 2006

Most yeast strains harbor extrachromosomal 2-micrometer DNA, and this DNA synthesis, like nuclear DNA replication, is strictly under cell cycle control. A soluble extract of yeast Saccharomyces cerevisiae carries out semiconservative replication of added 2-micrometer DNA and Escherichia coli chimeric plasmids containing the 2-micrometer DNA. Replication is initiated on 10% of the DNA, and one round of replication is completed. The major products in early stages of replication are theta ("eye") forms which originate 140 +/- 50 nucleotides within one of the 599-base-pair inverted repeats of 2-micrometer DNA. Their replication is bidirectional and discontinuous. Extracts prepared from the cell division cycle mutant cdc8 show temperature-sensitive 2-micrometer DNA synthesis in vitro, suggesting that this in vitro system resembles in vivo 2-micrometer plasmid DNA replication. This system should provide a useful assay for the purification and characterization of yeast DNA replication proteins.
Localization of the puromycin binding site on the large ribosomal subunit of Escherichia coli by immunoelectron microscopy.
Authors: Lührmann R , Bald R , Stöffler-Meilicke M , Stöffler G
Published: May 2006

By using immunoelectron microscopy, we have localized the binding site on 50S Escherichia coli ribosomal subunits for puromycin, an antibiotic that interacts with the ribosomal peptidyltransferase center. This was achieved by affinity-labeling 50S subunits with N-bromoacetyl puromycin and treating the labeled subunits with an antibody specific for the N6,N6-dimethyladenosine moiety of puromycin. The position of the puromycin binding site was then revealed by localizing the attachment sites of the IgG molecules on the surfaces of the 50S subunits under the electron microscope: it was located at the interface between the subunits, on and around the wider lateral protuberance of the 50S subunit. This localizes directly the peptidyl transferase center on the surface of the large ribosomal subunit.
Method for studying kinetics of light-induced transport across membranes.
Authors: Dewey T G , Hammes G G
Published: May 2006

A technique based on phase spectrophotometry is described for studying the rates of elementary processes associated with the light-driven transport of ions and molecules across membranes. The light-induced pumping of protons by bacteriorhodopsin reconstituted into phospholipid vesicles and by chloroplast thylakoids has been studied to illustrate the potential of this technique. The exciting light is modulated by a mechanical chopper over the frequency range 5 Hz to 2 kHz. The internal pH of the membrane vesicles is modulated at the same frequency as the exciting light but differs in phase because of the finite rate of proton pumping. Measurement of this phase difference or of the frequency dispersion of the amplitude of the internal pH modulation is accomplished by use of a lock-in amplifier. The results can be interpreted in terms of relaxation times characterizing the chemical steps in proton pumping. The shortest relaxation time that can be measured is about 50 microseconds, although the time resolution could be easily extended by use of faster light chopping techniques. At pH 8.0, two relaxation processes are associated with proton pumping by bacteriorhodopsin reconstituted into phospholipid vesicles; the relaxation times are 2 and 28 msec. Two relaxation processes also were found with chloroplast thylakoids at pH 7.8, with relaxation times of 2 and 16 msec. The former can be associated with photosystem II and the latter, with photosystem I.
Dissociative extraction and reconstitution of extracellular matrix components involved in local bone differentiation.
Authors: Sampath T K , Reddi A H
Published: May 2006

Subcutaneous implantation of demineralized diaphyseal bone matrix in allogeneic rats results in the local induction of endochondral bone differentiation. We have explored the potential of three dissociative extractants, 4 M guanidine hydrochloride (Gdn . HCl), 8 M urea/1 M NaCl, and 1% NaDodSO4 at pH 7.4, containing protease inhibitors to solubilize putative inductive molecules in the bone matrix. Extraction of bone matrix with any one of these extracts resulted in the loss of the bone inductive property. The solubilized extracts were then reconstituted with the residue by dialysis against water. The various reconstituted matrices were bioassayed for bone inductive potential by quantitation of alkaline phosphatase activity and 45Ca incorporation on day 12 after implantation. There was complete recovery of biological activity after reconstitution of the residues with each of the three extracts. Polyacrylamide gel electrophoresis of the extracts revealed similar protein profiles. Gel filtration of the 4 M Gdn. HCl extract on Sepharose CL-4B showed a heterogeneous broad peak. When fractions of that peak containing proteins less than 50,000 daltons were reconstituted with inactive 4 M Gdn . HCl-treated bone matrix and then implanted, new bone was induced. These observations demonstrate the dissociative extraction and successful biological reconstitution of bone inductive macromolecules in demineralized bone matrix.
DNA methylation and gene expression: endogenous retroviral genome becomes infectious after molecular cloning.
Authors: Harbers K , Schnieke A , Stuhlmann H , Jähner D , Jaenisch R
Published: May 2006

The Mov-3 substrain of mice carries Moloney murine leukemia virus as a Mendelian gene in its germ line. All mice segregating the Mov-3 locus activate virus and develop viremia and leukemia. The integrated provirus (i.e., Mov-3 locus) was molecularly cloned from Mov-3 liver DNA as a 16.8 kilobase long EcoRI fragment. Comparison of the cloned and genomic Mov-3 specific EcoRI fragment by restriction enzyme analysis showed no differences in the size of the fragments, indicating that no major sequence rearrangements occurred during cloning. The genomic and cloned Mov-3 DNAs were compared for methylation and infectivity. Analysis with Hha I showed that the genomic proviral and the flanking mouse sequences were methylated at cytosine residues, in contrast to the cloned Mov-3 locus. The cloned Mov-3 locus, however, was highly infectious in a transfection assay (1 x 10(-3) plaque-forming unit per viral genome) in contrast to the genomic Mov-3 DNA (less than 10(-7) per viral genome). Our results suggest that genes containing 5-methylcytosine are not expressed after transfection into susceptible cells and that removal of the methyl groups by molecular cloning in prokaryotes leads to expression generating infectious proviral DNA. If gene expression of transfected DNA is controlled by mechanisms that are relevant for gene expression in the animal, this suggests that DNA methylation may play a causative role in eukaryotic gene regulation.
Tubulin biosynthesis in the developmental cycle of a parasitic protozoan, Leishmania mexicana: changes during differentiation of motile and nonmotile stages.
Authors: Fong D , Chang K P
Published: May 2006

Cytodifferentiation in the transition cycle of the parasitic protozoan Leishmania mexicana amazonensis was studied in vitro. The flagellated motile promastigotes transform into the nonmotile amastigotes in 7 days at 35 degrees C intracellularly in the murine macrophage line J774G8. In medium 199 plus fetal bovine serum, the reverse transformation occurs extracellularly at 27 degrees C in 2 days. Slab gel electrophoresis of leishmanias labeled with [35S]methionine during transformation revealed changes in protein banding patterns. The intensity of two protein species with apparent molecular weights of approximately equal to 55,000 increased in the amastigote-to-promastigote differentiation and decreased during the reverse transformation. These two protein species comigrated approximately with alpha- and beta-tubulin of Chlamydomonas flagella in two-dimensional gel electrophoresis. The lower band was further identified as beta-tubulin by immunoprecipitation using rabbit antiserum specific to the beta-tubulin of Chlamydomonas axonemes. The biosynthetic change of tubulin was found to correlate with the morphological change of microtubules is leishmanial flagella and cytoskeleton during transformation.
Sequence relationships among the hemagglutinin genes of 12 subtypes of influenza A virus.
Authors: Air G M
Published: May 2006

Nucleotide sequences of the 3' 20% of the hemagglutinin gene of 32 influenza A virus strains from the 12 known hemagglutinin subtypes have been determined. Although the sequences of hemagglutinin genes and proteins of different subtypes differ greatly, cysteine and some other amino acid residues are totally conserved, presumably reflecting evolution of the 12 different hemagglutinins from a single gene. When viruses of one subtype, isolated over a period of time, are compared, the hemagglutinin gene and protein sequences show a slow accumulation of nucleotide changes and some amino acid changes. Since sequence data from the genes coding for the matrix and nonstructural proteins also show an accumulation of changes with time, it seems that antigenic selection (of the surface antigens) does not contribute significantly to the rate of change on influenza gene sequences. Although the rate of nucleotide change during drift is more than sufficient to account for the amino acid sequence differences observed in the 12 subtypes, there is a clear distinction, by antigenic as well as sequence analyses, between viruses of one subtype (0-9% amino acid variation) and viruses of other subtypes (20-74% amino acid variation). No virus has yet been found that is intermediate between subtypes.
Nitrate biosynthesis in man.
Authors: Green L C , Ruiz de Luzuriaga K , Wagner D A , Rand W , Istfan N , Young V R , Tannenbaum S R
Published: May 2006

Nitrate metabolism was investigated in long-term metabolic studies in healthy young men. Under conditions of constant low ingestion of nitrate (less than 180 mumol/day per subject), the amount of nitrate excreted in urine was an average of 4-fold greater than the amount ingested. Balance studies with 15NO3- showed that the source of the excess nitrate in urine was the endogenous biosynthesis of nitrate, rather than the emptying of a body pool. Nitrate biosynthesis occurred when nitrate ingestion was high as well as low, and the amounts synthesized appeared to be independent of intake and comparable to the amounts ingested from normal diets. Analysis of the 15NO3- data also revealed that half of ingested nitrate was recovered as urinary nitrate. Because nitrate in urine is the net result of (i) intake, (ii) endogenous synthesis, and (iii) metabolic losses, the magnitude of the losses is such that, despite ongoing synthesis, the amount of nitrate in the urine of people consuming most diets will be less than the amount ingested.
The behavioral effects of phencyclidines may be due to their blockade of potassium channels.
Authors: Albuquerque E X , Aguayo L G , Warnick J E , Weinstein H , Glick S D , Maayani S , Ickowicz R K , Blaustein M P
Published: May 2006

The action of phencyclidine [1-(1-phenylcyclohexyl)piperidine; PCP] and its behaviorally active analog (m-amino-PCP) and of two behaviorally inactive analogs [m-nitro-PCP and 1-piperidinocyclohexanecarbonitrile (PCC)] were examined in this study. In a test of spatial alternation performance in rats, PCP and m-amino-PCP were much more potent behavior modifiers than were PCC and m-nitro-PCP. We studied the effects of the drugs on the ionic channels of the electrically excitable membrane and of the nicotinic acetylcholine (AcCho) receptors at the neuromuscular junction of frog skeletal muscle. All four compounds blocked the indirectly elicited muscle twitch and depressed the amplitude and rate of rise of directly elicited muscle action potentials. They also caused a voltage- and concentration-dependent decrease in the peak amplitude of the endplate current but did not react with the nicotinic AcCho receptor. These observations indicate that the four compounds have comparable blocking effects on the ionic channels associated with the nicotinic AcCho receptor. In contrast, the behaviorally active agents could be distinguished from behaviorally inactive ones by their effects on K+ conductance. PCP and m-amino-PCP blocked delayed rectification in frog sartorius muscles, prolonged the muscle action potential more than 2-fold, and markedly potentiated the directly elicited muscle twitch. The behaviorally active compound also blocked depolarization-induced 86Rb+ efflux from rat brain synaptosomes (presumably a measure of K+ conductance) and increased quantal content at the frog neuromuscular junction. In these actions, m-nitro-PCP was much less effective, and PCC was relatively ineffective. Because PCP and m-amino-PCP are much more potent behavior modifiers than PCC and m-nitro-PCP, we suggest that the behavioral effects of PCP and m-amino-PCP, may be due to a block of K+ conductance and enhancement of transmitter release at central neurons.
Expanding the definition of the blood-brain barrier to protein.
Authors: Broadwell R D , Salcman M
Published: May 2006

Tight junctions between cerebral endothelial cells and the near absence of pinocytosis and vesicular transport of blood-borne protein into and across these cells are believed to constitute the mammalian blood-brain barrier. In the present investigation evidence is provided to indicate that the capillary endothelium of the mouse brain pinocytosis the enzymatic tracer horseradish peroxidase (EC 1.11.1.17) from cerebral blood under normal conditions. This protein and the internalized endothelial surface membrane associated with it are directed, for the most part, to acid hydrolase-positive lysosomes for degradation. Although peroxidase was never seen in the perivascular clefts, the lysosomes of pericytes were peroxidase-positive. Pericytes are macrophage-like cells located on the abluminal surfaces of cerebral microvasculature; these cells may serve as the first line of defense once the blood-brain barrier is breached. The definition of the blood-brain barrier should be expanded to include consideration of the lysosomal system of organelles in endothelial cells and pericytes.
Dimethyl sulfoxide prevents DNA nicking mediated by ionizing radiation or iron/hydrogen peroxide-generated hydroxyl radical.
Authors: Repine J E , Pfenninger O W , Talmage D W , Berger E M , Pettijohn D E
Published: May 2006

Eighty percent of the single-strand DNA breaks induced by gamma-irradiation were prevented by the hydroxyl radical (.OH) scavenger dimethyl sulfoxide (Me2SO); CH4 was generated in the process as a product of the interaction of .OH and Me2SO. In contrast, Me2SO completely blocked DNA nicking by an iron/H2O2 system which produces .OH but smaller amounts of CH4 from Me2SO. Because Me2SO prevented DNA breaks from the more efficient iron/H2O2 system but only blocked 80% of irradiation-mediated nicking, the results suggest that .OH is responsible for 80% of the DNA single-strand breaks and the remaining 20% is due to interactions not involving .OH.
Calcium lability of cytoplasmic microtubules and its modulation by microtubule-associated proteins
Authors: Schliwa Manfred , Euteneuer Ursula , Bulinski Jeannette Chloe , Izant Jonathan G.
Published: May 2006

Detergent-extracted BSC-1 monkey cells have been used as a model system to study the Ca
2+
sensitivity of
in vivo
polymerized microtubules under
in vitro
conditions. The effects of various experimental treatments were observed by immunofluorescence microscopy. Whereas microtubules are completely stable at Ca
2+
concentrations below 1 μM, Ca
2+
at greater than 1-4 μM induces microtubule disassembly that begins in the cell periphery and proceeds towards the cell center. At concentrations of up to 500 μM, both the pattern and time course of disassembly are not markedly altered, suggesting that, within this concentration range, Ca
2+
effects are catalytic rather than stoichiometric. Higher (millimolar) Ca
2+
concentration results in rapid destruction of microtubules. Of other divalent cations, only Sr
2+
has a slight depolymerizing effect, whereas millimolar Ba
2+
, Mg
2+
, or Mn
2+
is ineffective. Disassembly induced by micromolar Ca
2+
is inhibited by pharmacological agents known to bind to calmodulin and inhibit its function, suggesting that calmodulin mediates Ca
2+
effects. Both the addition of exogenous brain microtubule-associated proteins (MAPs) after lysis and the retention of endogenous cellular MAPs normally extracted during the lysis step stabilize microtubules against the depolymerizing effect of micromolar Ca
2+
. The results indicate that, in this model system, microtubules are sensitive to physiological Ca
2+
concentrations and that this sensitivity may be conferred by calmodulin associated with the microtubules. MAPs appear to have a modulating effect on microtubular Ca
2+
sensitivity and thus may function as a discriminating factor in cellular functions performed by calmodulin. It is hypothesized that Ca
2+
-stimulated microtubule disassembly depends on the relative amount of MAPs.
Structural brain mutant of
Drosophila melanogaster
with reduced cell number in the medulla cortex and with normal optomotor yaw response
Authors: Fischbach K. F. , Heisenberg M.
Published: May 2006

KS58, one out of six known alleles of the small optic lobes (
sol
) gene in
Drosophila melanogaster
, reduces the cell number in the medulla cortex by degeneration of ganglion cells in the pupae to about 50%. Also, about half the volume of the medulla and lobula complex neuropils is missing. Many Golgistained cells in the mutant optic lobes resemble their homologues in wild type. However, special classes of transmedullary columnar neurons projecting to the lobula or to both lobula and lobula plate are not seen in the mutant. Some neurons linking the lobula complex to the central brain send branches to the medulla (the branches do not exist in wild type); some other types seem to be missing. The fate mapping of the KS58 focus reveals a location ventral to the head bristles and in
sine oculis
(
so
) flies the mutation further reduces the rudiments of the optic lobes normally seen. Therefore the
sol
phenotype is not induced by mutant eyes and the primary gene action seems to be on nervous tissue. The structural alterations of the small optic lobes are reflected in visual orientation behavior. The optomotor yaw response, however, is almost quantitatively preserved. The respective neural network should still be present in the mutant optic lobes.
Cell cycle-dependent regulation of thymidine kinase activity introduced into mouse LMTK- cells by DNA and chromatin-mediated gene transfer.
Authors: Schlosser C A , Steglich C , deWet J R , Scheffler I E
Published: May 2006

We report on the expression of thymidine kinase (tk) activity in synchronized populations of mouse cells that have been transformed to the tk+ phenotype with purified DNA from various sources or with metaphase chromosomes from human cells. The viral (herpes) tk gene is constitutively expressed but, in all other cases examined, the activity is regulated as in normal tk+ mouse cells: There is a dramatic increase at the beginning of the S-phase. This regulation is observed whether the transgenome is stably integrated into the host genome or whether it is still in an unstable nonintegrated state.
Immunodiagnosis of hepatitis B with high-affinity IgM monoclonal antibodies.
Authors: Wands J R , Carlson R I , Schoemaker H , Isselbacher K J , Zurawski V R
Published: May 2006

High-affinity monoclonal IgG and IgM antibodies to hepatitis B surface antigen (HBsAg) have been prepared and their functional capabilities explored by means of solid-phase radioimmunoassays. 125I-labeled HBsAg binding studies indicated that monoclonal IgM antibodies against HBsAg (anti-HBs) coupled to a solid-phase support quantitatively bound more HbsAg at a faster rate than conventionally prepared anti-HBs reagents or other high-affinity IgG monoclonal anti-HBs antibodies. Consequently, IgM anti-HBs was also radiolabeled, and an IgM-IgM radioimmunoassay was developed for the immunodiagnosis of hepatitis B. The lower limit of this assay was approximately 100 pg +/- 30 (SEM) of HBsAg per ml of serum. Compared to available commercial radioassays, preliminary studies have shown the IgM-IgM assay to have increased sensitivity, which improved the detection of a HBsAg-associated determinant in acute hepatitis and post transfusion hepatitis. It is probable that the multivalent interaction between monoclonal IgM anti-HBs and the polydeterminant HBsAg is important in augmenting the performance of this monoclonal assay.
Sex choice and the size advantage model in jack-in-the-pulpit (
Arisaema triphyllum
)
Authors: Policansky David
Published: May 2006

Arisaema triphyllum
is a perennial herb whose sex and size often change from one growing season to the next. The proportional gain in reproductive success (
RS
) with size is much greater for female (carpellate) plants than it is for male (staminate) plants. I constructed
RS
-size curves for males and females; the curves intersect at a point
t
= 398 mm. According to theory derived from the size advantage model,
t
is the point below which the plants should be male and above which they should be female. Plots of size-frequency distributions of males and females show that below 380 mm the proportion of males is greater than the proportion of females, whereas above that point the proportion of females is greater than the proportion of males. Thus prediction and observed results are in very close conformity.
A construction of
F
1
as automorphisms of a 196,883-dimensional algebra
Authors: Griess Robert L.
Published: May 2006

In this note, I announce the construction of the finite simple group
F
1
, whose existence was predicted independently in 1973 by Bernd Fischer and by me. The group has order 2
46
3
20
5
9
7
6
11
2
13
3
17.19.23.29.31.41. 47.59.71 = 808,017,424,794,512,875,886,459,904,961,710,757,005,754,368,000,000,000 and is realized as a group of automorphisms of a 196,883-dimensional commutative nonassociative algebra over the rational numbers, which has an associative form. Equivalently, it is a group of automorphisms of a cubic form in 196,883 variables. It turns out that all the relevant arguments and calculations may be done by hand. Furthermore, existence of the group
F
1
implies the existence of a number of other sporadic simple groups for which existence proofs formerly depended on work with computers. We are beginning to look upon this group as a “friendly giant.”
Replication of herpes simplex virus DNA: localization of replication recognition signals within defective virus genomes.
Authors: Vlazny D A , Frenkel N
Published: May 2006

Serially passaged herpes simplex virus type 1 (HSV-1) strain Justin was previously shown to contain defective virus genomes consisting of head-to-tail reiterations of sequences derived from the end of the S component of the standard virus DNA. Cotransfection of purified monomeric defective genome repeat units with foster helper virus DNAs onto rabbit skin cells resulted in regeneration and replication of concatemeric defective DNA molecules which were successfully encapsidated. Thus, defective HSV-1 (Justin) genomes contain, within their limited DNA sequences, a sufficient set of recognition sites required for HSV DNA replication and packaging. The arrangement of repeat units within the regenerated defective virus genomes was consistent with their replication by a rolling circle mechanism in which a single repeat unit served as the circularized template. This replication occurred most actively late after infection and could be shown to be inhibited by low concentrations of phosphonoacetate known to inhibit the HSV-specified viral DNA polymerase selectively. The resultant concatemers were shown to be cleaved to Mr 100 X 10(6) DNA molecules which were terminated at one end with the proper ac end sequence of the parental standard virus DNA.
Expression of herpes simplex virus type I thymidine kinase gene in Escherichia coli.
Authors: Garapin A C , Colbère-Garapin F , Cohen-Solal M , Horodniceanu F , Kourilsky P
Published: May 2006

A herpes simplex virus type I DNA fragment containing the sequence coding for thymidine kinase was fused to the very beginning of the Escherichia coli lac Z gene in the three possible reading frames. When the thymidine kinase sequence was in the orientation fit to be transcribed from the lac promoter, functional thymidine kinase was made under lac control in all three cases. Sequences data indicate that translation reinitiation occurs at the 5' end of the thymidine kinase gene after stop signals. Two T+A-rich sequences, which may be part of eukaryotic promoters, are found in the same region.
Replication of adenovirus DNA-protein complex with purified proteins.
Authors: Ikeda J E , Enomoto T , Hurwitz J
Published: May 2006

A protein fraction isolated from the cytosol of adenovirus-infected HeLa cells, which contained DNA polymerase alpha, catalyzed adenoviral DNA replication in the presence of adenovirus DNA binding protein, eukaryotic DNA polymerase beta, ATP, all four dNTPs, and MgCl2. DNA replication started at either end of exogenously added adenoviral DNA and was totally dependent on the presence of terminal 55,000-dalton proteins on the DNA template. The replicaton of adenovirus DNA in the system was sensitive to aphidicolin and retained nearly all the properties of DNA replication that occur in vivo or in vitro with crude extracts. The 5'-ends of the newly synthesized adenovirus DNA strands were covalently linked to an 80,000-dalton protein linked to dCMP. DNA synthesized with purified proteins was only 25-50+ the length of parental viral strands. Addition of cytosol extracts from uninfected HeLa cells to reaction mixtures containing purified proteins gave full-length adenoviral DNA strands.
Metal cation influence on activity and regulation of aspartate carbamoyltransferase.
Authors: Honzatko R B , Lauritzen A M , Lipscomb W N
Published: May 2006

At saturating carbamoylphosphate and nonsaturating aspartate concentrations, Mg2+, Ca2+, Sr2+, Ba2+, Mn2+, Al3+, and Gd3+ inhibit aspartate carbamoyltransferase (carbamoylphosphate:L-asparate carbamoyltransferase, EC 2.1.3.2) from EScherichia coli. When nucleotide triphosphates are present, these inhibitory effects are displaced to higher concentrations of cation. At lower levels of cation and saturating carbamoylphosphate concentration, Mg2+, Mn2+, Al3+, and Gd3+ partially relieve allosteric inhibition by GTP but have little influence on activation by ATP and inhibition by CTP. At nonsaturating carbamoylphosphate concentrations, however, Mg2+, Mn2+, Al3+, and Gd3+ increase enzymatic activity to 170% over the level when GTP alone is present. In addition, Mg2+, Mn2+, and Al3+ show enhancement of ATP activation by 120-130% but only slight relief of CTP inhibition. We suggest that three modes of action by the metal can account for the observed kinetic behavior. (i) In the absence of nucleotide, metals inhibit catalytic activity either by a direct interaction with the enzyme or indirectly by complexing carbamoylphosphate. (ii) The metal-nucleotide complex interacts allosterically with the enzyme to enhance enzymatic activity relative to that produced by the free nucleotide, as noted above. (iii) By chelating to nucleotides, the metal diminishes their tendency to bind competitively at the carbamoylphosphate portion of the active site, as shown particularly by experiments on the catalytic subunit.
Specific recognition of apurinic sites in DNA by a tryptophan-containing peptide.
Authors: Behmoaras T , Toulme J J , Helene C
Published: May 2006

We have used fluorescence spectroscopy to study the binding of lysyltryptophyl-alpha-lysine (Lys-Trp-Lys) to DNA modified by dimethyl sulfate before and after depurination and strand breakage. Quenching of tryptophan fluorescence increased upon association of the peptide with modified DNA as compared with native DNA. We have demonstrated that this quenching is related to a preferential stacking of the indole ring with nucleic acid bases in damaged regions. Stacking increased in the following order: methylated DNA less than DNA with strand breaks at apurinic sites much less than apurinic DNA. For apurinic DNA, the overall association constant of Lys-Trp-Lys was increased by more than two orders of magnitude as compared to native DNA. Enhancement of the affinity of the tripeptide for an apurinic site requires the integrity of the phosphodiester bond. Single-strand cleavage at an apurinic site leads to a marked decrease of the association constant. The peptide Lys-Trp-Lys is therefore able to recognize destabilized regions in the vicinity of a lesion and to discriminate between different configurations of the damaged region. These results are discussed with respect to the role that stacking interactions could play in the specificity of recognition of DNA alterations by enzymes involved in DNA repair mechanisms.
Seismology and geodesy of the sun: Solar geodesy
Authors: Dicke R. H.
Published: May 2006

Measurements of the elliptical figure of the sun made in 1966 are analyzed on an hourly basis. This analysis yields an improved measure of the previously found solar distortion, rotating rigidly with a sidereal period of 12.38±0.10 days. It also yields a set of residùals used to search for signals due to low-frequency solar oscillations.
Digestibility of sorghum proteins.
Authors: Axtell J D , Kirleis A W , Hassen M M , D'Croz Mason N , Mertz E T , Munck L
Published: May 2006

Published information indicates that rice, maize, and wheat proteins are much more digestible in children than sorghum proteins are (66-81% compared with 46%). However, this digestibility difference cannot be demonstrated with the weanling rat, which gave digestibility values of 80% for cooked and 85% for uncooked sorghum gruels. Therefore, a search was made for a laboratory system sensitive to the digestibility differences between sorghum and other cereals. We found that porcine pepsin in vitro shows these digestibility differences. Using pepsin, we have found that uncooked sorghum proteins have a high digestibility (78-100%), which drops to a range of 45-55% after cooking. Two fermented sheet-baked sorghum products (kisra and abrey) from Sudan gave pepsin digestibility values of 65-86%. In contrast, unfermented cooked gruels made in our laboratory from the same flours used for the kisra and abrey gave pepsin values of only 44-56%. Therefore, fermentation improves pepsin digestibility of sorghum. The digestibility values of other sorghum-based foods prepared in the semiarid tropics need surveying. Those with high pepsin digestibility values hopefully should be more digestible (in children) than are the cooked sorghum gruels studied to date by human nutritionists.
Nucleotide sequences at the termini of phi 29 DNA.
Authors: Yoshikawa H , Friedmann T , Ito J
Published: May 2006

The nucleotide sequences of the first 422 base pairs from the left-hand end and the first 274 base pairs from the right-hand end of phi 29 DNA were determined by using the chemical degradation method of Maxam and Gilbert. The data indicate that phi 29 DNA has inverted terminal repetitions that are six base pairs long 5' (-A-A-A-G-T-A-). No perfectly self-complementary sequence exists within the terminal regions of phi 29 DNA, suggesting that DNA replication via a self-priming mechanism is improbable. The putative early promoter sequences were found in both ends of the phi 29 DNA. The results of the sequence determination are discussed in relation ship to models proposed for the mechanism of replication of linear DNA molecules.
Conservation of the primosome in successive stages of phi X174 DNA replication.
Authors: Low R L , Arai K , Kornberg A
Published: May 2006

Synthesis of a complementary strand to match the single-stranded, circular, viral (+) DNA strand of phage phi X174 creates a parental duplex circle (replicative form, RF). This synthesis is initiated by the assembly and action of a priming system, called the primosome [Arai, K. & Kornberg, A (1981) Proc. Natl. Acad. Sci. USA 78, 69-73; Arai, K., Low, R. L. & Kornberg, A. (1981) Proc. Natl. Acad. Sci. USA 78, 707-711]. Of the seven proteins that participate in the assembly and function of the primosome, most all of the components remain even after the DNA duplex is completed and covalently sealed. Remarkably, the primosome in the isolated RF obviates the need for supercoiling of RF by DNA gyrase, an action previously considered essential for the site-specific cleavage by gene A protein that starts viral strand synthesis in the second stage of phi X174 DNA replication. Finally, priming of the synthesis of complementary strands on the nascent viral strands to produce many copies of progeny RF utilizes the same primosome, requiring the addition only of prepriming protein i. thus a single primosome, which becomes associated with the incoming viral DNA in the initial stage of replication, may function repeatedly in the initiation of complementary strands at the subsequent stage of RF multiplication. These patterns of phi X174 DNA replication suggest that a conserved primosome also functions in the progress of the replicating fork of the Escherichia coli chromosome, particularly in initiating the synthesis of nascent (Okazaki) fragments.
Flow kinetics of mouse histocompatibility antigens.
Authors: Croze E M , Morré D J
Published: May 2006

Major histocompatibility antigens of the mouse (H-2 antigens) are found on a variety of different cell types and constitute a class of integral membrane-bound glycoproteins involved in tissue graft rejection and immune surveillance. We used monospecific alloantibodies directed against mouse H-2 antigens and standard pulse-chase technique to investigate the flow kinetics of delivery of newly synthesized membrane constituents to the cell surface. [35S]Methionine was injected intraperitoneally, and, after a chase with unlabeled methionine, livers were excised and fractionated into endoplasmic reticulum, Golgi apparatus, and plasma membrane fractions. Label first appeared in H-2 antigens located within the endoplasmic reticulum. Maximum specific activity observed between 5-7 min after injection of label was followed by a rapid loss of label. H-2 antigens of Golgi apparatus also were labeled early. Peak specific activity observed 15-25 min after injection of label was again followed by rapid loss of label. H-2 antigens of the plasma membrane were labeled last and appeared to accumulate radioactivity with no evidence of rapid turnover. These results provide evidence for a precursor-product relationship between H-2 antigens located within the cell on membranes of endoplasmic reticulum and Golgi apparatus and those on the plasma membrane. Flow of individual membrane-bound glycoproteins from their sites of synthesis and insertion into the membrane of the endoplasmic reticulum to the plasma membrane through the Golgi apparatus is indicated.
Cloning of mouse immunoglobulin epsilon gene and its location within the heavy chain gene cluster.
Authors: Nishida Y , Kataoka T , Ishida N , Nakai S , Kishimoto T , Böttcher I , Honjo T
Published: May 2006

Mouse immunoglobulin epsilon chain gene was cloned from DNA of a hybridoma producing anti-dinitrophenyl IgE, which was constructed by fusing a spleen cell of a BALB/c mouse with a variant clone of MOPC21 myeloma (IgG1 producer). Because a given active heavy chain constant region (CH) gene is linked to a heavy chain joining segment (JH) gene at its 5' side, the expressed C epsilon gene of the hybridoma was cloned from a phage library containing partial Sau3A digests of IgE hybridoma DNA by using a J gene fragment as a probe. Among 6 X 10(5) phages screened, five positive clones were obtained and three of them were identified as C epsilon gene clones by restriction mapping, Southern blot hybridization, R-loop formation, and partial nucleotide sequence determination. The determined nucleotide sequence predicted the amino acid sequence which resembles a part of the CH3 domain of human epsilon chain. The deletion profile of the C epsilon gene in various myelomas expressing different CH genes indicates that the C epsilon gene is located between the C gamma 2a and C alpha genes. The linkage (5'-epsilon-alpha-3') was directly confirmed by molecular cloning of the overlapping chromosomal segments from newborn mouse DNA.
NMR studies of 5-hydroxytryptamine transport through large unilamellar vesicle membranes.
Authors: Viscio D B , Prestegard J H
Published: May 2006

Nuclear magnetic resonance techniques developed to study membrane permeability in closed membrane systems have been used to investigate transport of 5-hydroxytryptamine across the phospholipid membranes of large unilamellar vesicles. The vesicles, modeling the 5-hydroxytryptamine storage organelles of blood platelets, contained a high internal level of ATP buffered at a pH low relative to the external solution. The resultant pH gradient drove accumulation of 5-hydroxytryptamine to a level consistent with selective transport of the neutral amine. The upfield shifts of the 5-hydroxytryptamine resonances resulting from complexation with internally confined ATP were utilized to resolve and, simultaneously, to observe the internal and external amine. Simulation of the time evolution of the 5-hydroxytryptamine concentration allowed measurement of a permeability coefficient of 1.4 +/- 0.5 X 10(-5) cm/sec for the neutral amine.
Accumulation of protoporphyrin IX and Zn protoporphyrin IX in
Cyanidium caldarium
Authors: Csatorday K. , MacColl R. , Berns D. S.
Published: May 2006

In vivo
fluorescence studies of
Cyanidium caldarium
mutants grown in the dark in dextrose-containing media have shown that these organisms accumulate protoporphyrin IX. In the dark the accumulated protoporphyrin IX is gradually turned into a metalloporphyrin, Zn protoporphyrin. In the light, in the chlorophyll-lacking mutant GGB, both compounds are degraded and phycobiliproteins are formed. These results implicate protoporphyrin IX
in situ
as the general precursor to tetrapyrrole pigments and Zn protoporphyrin IX as a possible intermediate or regulator in the biosynthesis of phycobilins.
Instability of integrated viral DNA in mouse cells transformed by simian virus 40.
Authors: Hiscott J B , Murphy D , Defendi V
Published: May 2006

The state and organization of simian virus 40 (SV40) DNA in tsA mutant-transformed mouse clones were examined early after agar selection in an attempt to elucidate the mechanisms that actively generate the diverse integration patterns found in transformed cells. Although recently selected as a cloned population from agar, A21 cells displayed extremely heterogeneous SV40 DNA patterns when analyzed by agarose gel electrophoresis and Southern blot hybridization. Reselection of clones in agar from A21 at 33 degrees C or 39.5 degrees C and DNA analysis by hybridization demonstrated (i) simplification of the number of integration sites in the new clones; (ii) new sites of integrated SV40 DNA in high molecular weight cell DNA fragments generated by digestion with restriction endonuclease Bgl II; (iii) relatedness between clones with respect to integrated viral sequence arrangement; and (iv) persistence of free viral DNA forms. The majority of free viral DNA appeared to be full length, nondefective SV40 DNA, although a subpopulation of defective viral molecules was also detected. No detectable free SV40 DNA could be observed in A21 clonal derivatives isolated by growth in agar at 39.5 degrees C, indicating that the persistence of free viral forms was regulated by the A gene. These results suggest that the heterogeneity in viral sequences in the A21 cells was generated within a cloned population from which new clones can be derived with different transformed phenotypes and integration patterns.
Passage of an integral membrane protein, the vesicular stomatitis virus glycoprotein, through the Golgi apparatus en route to the plasma membrane.
Authors: Bergmann J E , Tokuyasu K T , Singer S J
Published: May 2006

The intracellular pathway of biogenesis of the vesicular stomatitis virus transmembrane glycoprotein was investigated in situ by using indirect immunofluorescence of whole infected Chinese hamster ovary cells and immunoelectron microscopy of ultrathin frozen sections of infected cells. Transport of the glycoprotein was synchronized by using the temperature-sensitive virus mutant Orsay-45 and a temperature shift-down protocol. Sequential appearance of the glycoprotein in the rough endoplasmic reticulum, Golgi apparatus, and plasmalemma was demonstrated. The potential of this system for further studies is discussed.
Studies of a human T lymphocyte antigen recognized by a monoclonal antibody.
Authors: Engleman E G , Warnke R , Fox R I , Dilley J , Benike C J , Levy R
Published: May 2006

A monoclonal antibody (designated L17F12) detects an antigen present on 95-100% of human peripheral T lymphocytes, the majority of thymocytes, and acute lymphocytic leukemia T cells but not B cells, B-cell lines, or monocytes. Examination of frozen tissue sections by the immunoperoxidase method revealed that the cells expressing this antigen were found predominantly in the medulla of thymus and in T-cell zones of lymph node and spleen. The antigen recognized by L17F12 was associated with a cell-surface glycoprotein of 67,000 daltons. L17F12 was used to isolate this molecule from human thymocytes, normal peripheral T cells, leukemic T cells, and T-cell lines. Expression of this antigen on normal T cells was not diminished by prolonged exposure in vitro to various T-cell stimuli. In the absence of complement, L17F12 bound to T cells without altering proliferative functions, thus enabling rapid purification of functionally intact T cells. In the presence of complement, L17F12 was cytolytic for T cells, providing the basis for depletion of T cells from heterogeneous populations. These data suggest that the monoclonal antibody L17F12 recognizes a specific T-cell differentiation protein. This antibody will be useful in studies of the human immune system.
Expression of IgD may use both DNA rearrangement and RNA splicing mechanisms
Authors: Moore K. W. , Rogers J. , Hunkapiller T. , Early P. , Nottenburg C. , Weissman I. , Bazin H. , Wall R. , Hood L. E.
Published: May 2006

From a library of mouse sperm DNA, we have isolated two overlapping clones which contain the
C
δ
gene. One of these clones also contains the
C
μ
gene. The
C
δ
gene is separated from the
C
μ
membrane exons by approximately 2 kilobases (kb) of DAN. The
C
δ
gene was identified by (
a
) hybridization to poly(A)
+
RNA prepared from the IgD-producing rat plasma cell tumor IR731, and (
b
) homology of a translated nucleotide sequence to the amino acid sequence of the human δ chain. The
C
δ
gene spans 8 kb of DNA in the germ line. Plasmid subclones of the
C
δ
gene were used as probes in Southern and RNA blot experiments. RNA blot analysis of cytoplasmic poly(A)
+
RNA from IR731 and a μ
+
δ
+
B-cell hybridoma revealed 1.6- and 2.7-kb δ mRNA species with different 3′ ends, which presumably encode the secreted and membrane-bound forms, respectively, of the δ chain. Southern blot analysis of DNA from two μ
+
δ
+
lymphomas revealed that the
C
δ
gene is in the germ-line configuration in each case. Restriction map analysis of
C
μ
and
C
δ
genomic clones isolated from a library of normal μ
+
δ
+
B-cell DNA also gave no evidence for DNA rearrangement in the region between the
C
μ
and
C
δ
genes. Taken together, these data suggest that IgD expression in μ
+
δ
+
B cells does not involve a
V
H
-to-
C
δ
DNA switch rearrangement. We propose that simultaneous expression of
C
δ
and
C
δ
with a single
V
H
gene is mediated by two alternative routes of RNA processing of a primary nuclear transcript which contains the
V
H
,
C
μ
, and
C
δ
genes. In contrast, analogous experiments with myeloma IR731 DNA revealed that the
C
μ
gene has been deleted from the myeloma DNA and that the
C
δ
gene has undergone DNA rearrangement, presumably including a switch recombination of the
V
H
gene from the
C
μ
to the
C
δ
gene. These results indicate that two alternative mechanisms may be used in the expression of IgD molecules—RNA splicing in B cells and DNA rearrangement in plasma cells.
Reconstitution of Ir genes, Ia antigens, and mixed lymphocyte reaction determinants by gene complementation.
Authors: Fathman C G , Kimoto M , Melvold R , David C S
Published: May 2006

By using clones of murine T cells reactive with alloantigens as well as soluble antigens, it has been possible to demonstrate that Ia antigens, Ir gene phenomena (defined as the ability of immune T cells to recognize antigen), and mixed lymphocyte reaction (MLR)-stimulating determinants encoded within the I-A subregion are different manifestations associated with same product. These studies utilized the I-Ab mutant mouse B6.C-H-2bm (bm12), whose defect in the normal expression of the cell surface products of the I-Ab subregion can be partially circumvented through trans-complementation by deriving hybrids between bm12 and mice expressing normal I-A subregion products. Such mice [e.g., (bm12 X B10.A)F1] express several serologically normal I-Ab products but have defects in certain I-A subregion gene products normally expressed on cells of H-2a X H-2b heterozygote mice that are used as restricting elements for antigen recognition by antigen-reactive T cell clones or recognized as alloantigens by alloreactive T cell clones. This defect in cell surface expression of certain normal I-Ab products on the mutant bm12 cells has allowed us to suggest that there exist trans-complementing products on H-2a X H-2b heterozygote mice consisting of Ab alpha Ak beta and Ak alpha Ab beta that restrict antigen recognition by cloned T cells, stimulate MLR responses by cloned T cells, and react with certain anti-Ia antisera.
Boundary-layer model for the population dynamics of single species
Authors: Hastings Alan , Serradilla Juan M. , Ayala Francisco J.
Published: May 2006

We develop a new discrete-time model, called the boundary-layer model, to describe the dynamics of single species that have a capacity for fast growth at very low population densities. The model explicitly separates the dynamics of the population at very low densities (within the “boundary layer”) and at high densities. The boundary-layer model provides a better fit than other models such as the logistic or the θ model to data from experimental populations of
Drosophila willistoni
and
D. pseudoobscura.