bluuebunny/crossref_metadata_2025 huggingface dataset:
Purification of cytoplasmic tubulin and microtubule organizing center proteins functioning in microtubule initiation from the alga Polytomella.
Authors: Stearns M E , Brown D L
Published: May 2006

Cytoplasmic tubulin and the microtubule organizing centers (MTOCs) for the cytoskeletal microtubule system of the flagellate Polytomella have been isolated. The isolated MTOCs serve as sites for the in vitro assembly of the purified tubulin protein. The major proteins (four polypeptides of molecular weights 190,000-210,000) functioning in this assembly have been extracted from the MTOCs and purified. Kinetic studies and experiments with in vivo 35S-labeled MTOC proteins (or 35S-labeled tubulin) demonstrate that these proteins function specifically in microtubule initiation and do not contribute to microtubule elongation. The results indicate that microtubule assembly in vivo is controlled by microtubule initiating proteins associated with the organelles termed MTOCs.
Dynein binds to and crossbridges cytoplasmic microtubules.
Authors: Haimo L T , Telzer B R , Rosenbaum J L
Published: May 2006

Dynein isolated from Chlamydomonas flagellar axonemes binds to microtubules assembled in vitro from 6S brain tubulin dimers. The dynein arms bind periodically along the length of the microtubules with a center-to-center spacing of 24 nm, equal to the periodicity of dynein arms on intact axonemes. The arms project from the in vitro assembled microtubules at an angle of approximately 55 degrees, thereby defining microtubule polarity. Dynein cosediments with microtubules through a sucrose gradient, as demonstrated by electron microscopy, gel electrophoresis, and ATPase analysis. In addition, dynein induces crossbridging between adjacent microtubules. Darkfield microscopy reveals that microtubules containing dynein are aggregated into large bundles; electron microscopy indicates that microtubules of the same polarity are crossbridged by a regular array of arms. Viewed by darkfield microscopy, addition of ATP to crossbridged microtubules causes their disaggregation; electron microscopy shows that the majority of these microtubules are no longer crossbridged. These observations are applicable to the determination of microtubule polarity and directionality of microtubule assembly in situ and suggest a role for dynein in cytoplasmic microtubule-based cellular movements.
Effects of opiates and demographic factors on DNA repair synthesis in human leukocytes.
Authors: Madden J J , Falek A , Shafer D A , Glick J H
Published: May 2006

DNA repair synthesis in leukocytes stressed by far UV irradiation was studied in 90 normal individuals, 38 street-heroin addicts, and 18 methadone maintenance patients. Age, sex, coffee use, and alcohol use had no significant effect on the maximal repair synthesis response of the control subjects, but smoking tobacco significantly decreased the mean response and variance when compared with nonsmoking controls. Heroin addiction had an even more pronounced negative effect, and this may be related to the high rate of chromosome aberrations found in this population. Half of the addicts tested were incapable of repairing UV fluences one-quarter as large as those repaired by the control subjects (5 J/m2 and 20 J/m2, respectively) in the 2-hr assay period. Long-term methadone treatment ameliorated the effects of the street heroin, just as it resulted in a decrease of the chromosome aberration frequency.
Genetic variability maintained in a finite population under mutation and autocorrelated random fluctuation of selection intensity
Authors: Takahata Naoyuki , Kimura Motoo
Published: May 2006

By using the diffusion equation method, the level of genetic variability maintained under mutation pressure in a finite population is investigated, assuming autocorrelated random fluctuation of selection intensity. An appropriate mathematical model was formulated to treat the change of gene frequencies, incorporating mutation pressure and fluctuating selection. Extensive Monte Carlo simulation experiments were also performed to supplement the theoretical treatments. Excellent agreement between the two results suggests the validity of the present diffusion model for the autocorrelated selection. One of the most important findings from the simulation studies is that mutations and random sampling drift largely determine the level of genetic variability, and that the presence of autocorrelated selection can significantly lower genetic variability only when its strength, as measured by the cumulative variance of selection intensity, is larger than about 10
3
times the mutation rate. It is pointed out that the effects of both mutations and random sampling drift have to be incorporated in order to assess the role of various factors for the maintenance of genetic variability in natural populations.
Human lymphocyte antigens: production of a monoclonal antibody that defines functional thymus-derived lymphocyte subsets.
Authors: Haynes B F , Eisenbarth G S , Fauci A S
Published: May 2006

A monoclonal mouse antibody (3A1) that specifically bound to 65% of human peripheral blood (PB) thymus-derived (T) cells but did not bind to complement receptor-positive PB bone marrow-derived (B) cells, polymorphonuclear leukocytes, or human erythrocytes has been produced. The 3AI antibody was synthesized by a stable cloned lymphocyte hybrid cell line. This lymphocyte hybrid line (3AI) was derived from fusion of P3 X 63/Ag8 myeloma cells and spleen cells from BALB/c mice immunized with HSB-2 cells, a human T cell line. The 3A1 lymphocyte hybrid line produced mouse ascites fluid containing 3A1 antibody in saturating titers of up to 1:25,600. Purified PB T cells that carried the 3A1 antigen incorporated tritiated thymidine maximally in response to phytohemagglutinin and concanavalin A stimulation, whereas purified PB T cells that lacked the 3A1 antigen responded suboptimally to phytohemagglutinin and minimally to concanavalin A. Thus, the 3A1 antibody can be easily used to study the role of 3A1-positive and negative T cell subsets in the regulation of normal and abnormal human immune responses.
Distribution of active and inactive forms of endorphins in rat pituitary and brain.
Authors: Zakarian S , Smyth D
Published: May 2006

The recent isolation and identification of alpha-N-acetyl forms of the C-Fragment of lipotropin (beta-endorphin, residues 61-91) and the C'-Fragment (residues 61-87) [Smyth, D.G., Massey, D.E., Zakarian, S. & Finnie, M. (1979) Nature (London) 279, 252-254] has led to a study of their distribution in the pituitary and brain of the rat. Regions were mapped by the method of immunofluorescent staining and the reactive peptides were determined by immunoassay after extraction, gel filtration, and ion exchange chromatography. The major immunoreactive peptides in both lobes of the pituitary were found to be C'-Fragment and N-acetyl C'-Fragment, which are weakly active or inactive as opiates; the C-Fragment and its N-acetyl derivative represented minor components. This indicates that in the rat the circulating "endorphins" released from pituitary would have little morphinomimetic activity. The same four immunoreactive peptides were observed in rat brain. In the hippocampus the C'-Fragment was the principal component in the midbrain there was more C-Fragment but C'-Fragment predominated; in the hypothalamus the C-Fragment was the major peptide, almost to the exclusion of the other peptides. The results demonstrate that the processing of lipotropin is under differential control in anatomically distinct regions of the central nervous system. The processing of lipotropin in the hypothalamus is directed specifically to the production of lipotropin C-Fragment.
Intracellular dye-marked enkephalin neurons in the magnocellular preoptic nucleus of the goldfish hypothalamus.
Authors: Reaves T A , Hayward J N
Published: May 2006

A method that combines intracellular recording, dye marking, and immunocytochemistry makes the study of functional and morphological aspects of enkephalin neurons in the magnocellular preoptic nucleus of the goldfish hypothalamus feasible. By use of multiple techniques, enkephalin neurons can be distinguished from other brain cells and can be reconstructed from drawings of serial sections containing the dye-injected opioid cells. These enkephalin cells and their processes measure 14-42 micron in somata diameter and are unipolar, bipolar, or multipolar. Their electrophysiological properties match those of other mammalian and fish magnocellular endocrine cells. This report confirms the one neuron-one hormone (peptide) hypothesis, supports synaptic over electronic coupling between enkephalin and adjacent hypothalamic neurons, and suggests that chemical and functional classification of single electrophysiologically and neuroanatomically studied central neurons can be achieved.
Treatment of nerve impulse data for comparison with theory.
Authors: Knight B W , Brodie S E , Sirovich L
Published: May 2006

A procedure is given for the comparison of nerve impulse data with model predictions. This method utilizes information in the nerve impulse train that is ignored by the post-stimulus-onset histogram and thereby gives an improved signal-to-noise ratio. Comparison of observed responses in the Limulus retina with predictions derived from a detailed model gives good agreement.
Action of cathepsin D on human beta-lipotropin: a possible source of human "beta-melanotropin".
Authors: Barát E , Patthy A , Gráf L
Published: May 2006

Highly purified calf brain cathepsin D (EC 3.4.23.5) selectively splits the Leu77-Phe78 and Ala36-Ala37 peptide bonds of human beta-lipotropin. It is suggested that the formation of human "beta-melanotropin" from gamma-lipotropin, and that of gamma-endorphin from beta-endorphin, is due to the action of cathepsin D during isolation procedures.
Metal-coordinating substrate analogs as inhibitors of metalloenzymes.
Authors: Holmquist B , Vallee B L
Published: May 2006

A group of active-site metal coordinating inhibitors of zinc proteases (carboxypeptidase A, thermolysin, Bacillus cereus neutral protease, and angiotensin-converting enzyme) have been synthesized and their properties investigated. Their general structures are R-SH and R-NH-PO2(O phi)H, where-S- or -O- serve as metal ligands and R refers to an amino acid or peptide group designed to interact with substrate recognition sites. These inhibitors can be extremely potent; thus, N-(2-mercaptoacetyl)-D-phenylalanine, e.g., inhibits carboxypeptidase A with a Kiapp of 2.2 x 10(-7) M. The spectral response of cobalt(II)-substituted thermolysin or carboxypeptidase A to the sulfur-containing inhibitors signals the direct interaction of the mercaptan with the metal. An S leads to Co(II) charge transfer band is generated near 340 nm and is detected by absorption, circular dichroism, and magnetic circular dichroism. The cobalt(II) spectra indicate both inner sphere coordination with sulfur and 4-coordination in the enzyme-inhibitor complex. Thus, the metal undergoes a simple substitution reaction, the inhibitor most likely displacing water at the fourth coordination site.
Nonhormonal induction of H
+
efflux from plant tissues and its correlation with growth
Authors: Vesper Mary Jo , Evans Michael L.
Published: May 2006

When the esterase substrate α-naphthyl acetate is added to segments from coleoptiles of oat (
Avena sativa
L., var. Victory) or corn (
Zea mays
L., Bear hybrid WF 9 × 38) or to roots of lentil (
Lens culinaris
Med.), it is rapidly taken up and hydrolyzed to α-naphthol and acetic acid. This technique was used to generate intracellular acid and to study the effect of its efflux on growth. With corn coleoptile segments, treatment with α-naphthyl acetate induced more rapid and more prolonged growth than did exposure to external acidic buffers. Dose—response studies of α-naphthyl acetate induction of H
+
secretion and growth indicated the existence of a distinct threshold rate of H
+
efflux below which growth is not enhanced. The rate of H
+
efflux induced by optimal levels of auxin appears to be at or below this threshold level in corn coleoptile tissue. These data indicate that the relationship between external acidification and elongation is not a simple one and that the effectiveness of H
+
entering the cell wall may depend on factors not directly correlated with the appearance of H
+
in the external medium.
Microenvironmental influences on the in vivo behavior of neoplastic lymphocytes.
Authors: Diamandopoulos G T
Published: May 2006

A transplantable hamster lymphocytic neoplasma of probable monoclonal derivation, induced by the oncogenic DNA simian virus 40, has been adapted to grow in the allogeneic host either as leukemia (characterized by dissemination and poor prognosis) or as lymphoma (characterized by localization and favorable prognosis) [Diamandopoulos, G. Th. (1978) Proc. Natl. Acad. Sci. USA 75, 2011-2015]. In the present experiments the circumstances under which neoplastic lymphocytes that are transplanted in allogeneic animals retain, lose, or regain the capacity for dissemination or localization are assessed. Results indicate that the in vivo behavior of neoplastic lymphocytes is not a stable, irreversible characteristic that is transmitted to the cell progeny. On the contrary, it can be altered by the origin/tissue microenvironment in which the cells proliferate. It is suggested that, whereas neoplastic cell mutation followed by host selection could be responsible for changes in cell behavior, a more likely explanation is that the proliferating neoplastic lymphocytes acquire reversible nonmutational phenotypic characteristics during their interaction with the host microenvironment, which modify their behavior and, as a result, the prognosis of the neoplastic process.
Dynorphin-(1-13), an extraordinarily potent opioid peptide.
Authors: Goldstein A , Tachibana S , Lowney L I , Hunkapiller M , Hood L
Published: May 2006

We describe the opioid properties of a tridecapeptide, the sequence of which corresponds to the NH2-terminal sequence of dynorphin, a novel porcine pituitary endorphin. It contains [Leu]enkephalin. In the guinea pig ileum longitudinal muscle preparation it is about 700 times more potent than [Leu]enkephalin. Its effects in this tissue are blocked completely by naloxone, but the apparent affinity of naloxone is 1/13th that for blockade of [Leu]enkephalin or normorphine. In the mouse vas deferens, this peptide is 3 times more potent than [Leu]enkephalin. Well-washed rat brain membranes degrade the peptide rapidly, suggesting the presence of a membrane-bound degradative enzyme. The peptide displays considerable immunoreactivity in assays with antisera that have been used for the immunohistochemical localization of [Leu]enkephalin. The remarkable enhancement of the potency of [Leu]enkephalin by the COOH-terminal extension -Arg-Arg-Ile-Arg-Pro-Lys-Leu-Lys-OH suggests new interpretations concerning the structure of opiate receptors and the function of the enkephalin pentapeptides.
Structure of poly(adenosine diphosphate ribose): identification of 2'-[1''-ribosyl-2''-(or 3''-)(1'''-ribosyl)]adenosine-5',5'',5'''-tris(phosphate) as a branch linkage.
Authors: Miwa M , Saikawa N , Yamaizumi Z , Nishimura S , Sugimura T
Published: May 2006

Poly([14C]adenosine diphosphate ribose) was synthesized from [14C]NAD+ with calf thymus nuclei. The fraction containing poly(adenosine diphosphate ribose) eluted with 0.22--0.40 M phosphate buffer (pH 6.8) from a hydroxylapatite column, was completely hydrolyzed with venom phosphodiesterase, and was separated by DEAE-Sephadex A-25 column chromatography in 7 M urea. A new compound, which constituted 2% of the products from poly(adenosine diphosphate ribose), was found in addition to the expected products--i.e., 5'-AMP, 2'-(1''-ribosyl)adenosine-5',5''-bis(phosphate), and its derivatives. This compound was identified as 2'-[1''-ribosyl 2''-(or 3''-)(1'''-ribosyl)]adenosine-5',5'',5'''-tris(phosphate). The existence of this compound is evidence of a branching structure of poly(adenosine diphosphate ribose), which was previously thought to be a linear molecule. The content of this compound suggests that the frequency of branching is about 1 per 20--30 adenosine diphosphate ribose residues of high molecular weight poly(adenosine diphosphate ribose).
Preparative and analytical purification of DNA from agarose.
Authors: Vogelstein B , Gillespie D
Published: May 2006

Two procedures were developed for removing DNA from agarose after electrophoretic separation of DNA fragments according to size. Both involve dissolving the DNA-containing agarose in NaI. The preparative technique uses binding of DNA to glass in the presence of NaI. The method is rapid and convenient, and DNA of all molecular weight ranges can be recovered in high yield and without degradation. The DNA is free of agarose and remains susceptible to digestion by restriction enzymes. The analytical technique uses selective precipitation of DNA with acetone and has been adapted to molecular hybridization scans of sequences in agarose gels. The sequence-monitoring system is quantitative, directly measuring the proportion of the probe complementary to a given DNA fragment and vice versa. It is especially suitable for analyzing restriction enzyme digests of DNA in mapping experiments.
Vibrational analysis of peptides, polypeptides, and proteins: Characteristic amide bands of β-turns
Authors: Bandekar Jagdeesh , Krimm S.
Published: May 2006

Normal vibration calculations have been done for a type I β-turn of CH
3
-CO-(Ala)
4
-NH-CH
3
and a type II β-turn of CH
3
-CO-(Ala)
2
-Gly-Ala-NH-CH
3
. The force field was the one we refined for β-sheet and α-helical structures. A calculation was also done for CH
3
-O-CO-Gly-(Ala)
2
-Gly-O-CH
3
, which is an appropriate model for two tetrapeptides for which infrared data are available. The agreement between observed and calculated frequencies in this case is good, thus supporting the conclusions drawn from the above β-turn calculations. The most important result of the calculations is the prediction of bands near 1690 cm
-1
, a region heretofore associated only with the antiparallel-chain pleated sheet structure. This means that bands observed in proteins near 1690 cm
-1
should be associated with the presence of β-turns as well as of β-sheets. We also find that a band near 1665 cm
-1
is characteristic of type II turns.
Tumor initiators and promoters in the induction of Epstein—Barr virus
Authors: Hausen Harald zur , Bornkamm Georg W. , Schmidt Rainer , Hecker Erich
Published: May 2006

The effect of various tumor initiators and promoters on induction of persisting Epstein-Barr virus (EBV) in different lines of lymphoblastoid cells was analyzed. Neither five polycyclic aromatic hydrocarbons, amongst them potent tumor initiators (e.g., 7,12-dimethylbenz[
a
]anthracene), nor the potent (ultimate) liver carcinogen
N
-acetoxy-
N
-2-acetylamino-fluorene induced EBV. A series of compounds, representing three classes of tumor-promoting diterpene esters (e.g., 12-
O
-tetradecanoylphorbol-13-acetate), efficiently induced EBV in persistently infected cells. The concentration required for maximal induction ranged between 0.5 and 100 nM. Some nonpromoting diterpenes (phorbol, 4α-phorbol-12,13-didecanoate, and ingenol) did not induce EBV. However, the nonpromoters, resiniferatoxin and 12-deoxyphorbol-13-decatrienoate, were effective, whereas anthralin, a tumor promoter, did not induce EBV. In three lines of EBV genome-carrying cells (Raji, NC-37, and RPMI 64-10) only abortive induction was noted, leading exclusively to synthesis of early antigen. In cells of lines with low spontaneous virus release (P3HR-1, B95-8, and QIMR-Wil), upon treatment with tetradecanoylphorbol acetate, approximately 20-40 times more viral DNA was recovered as compared to untreated controls. Viral DNA from tetradeca-noylphorbol acetate-induced cultures revealed the same restriction endonuclease cleavage pattern as viral DNA obtained from noninduced cells. Within 10 days after induction, release of infectious virus increased approximately by one order of magnitude. Prostaglandins, reported to be released after treatment with tumor promoters, were ineffective in virus induction under the conditions tested.
Sequence-specific DNA uptake in Haemophilus transformation.
Authors: Sisco K L , Smith H O
Published: May 2006

Haemophilus cells efficiently take up Haemophilus DNA from the medium during transformation but do not take up other DNAs. To study the mechanism of this specificity we have cloned an 8.1-kilobase (kb) fragment of H. parainfluenzae DNA in the escherichia coli--pBR322 host--vector system and reisolated the DNA fragment for use as a defined probe. The 5'32P end-labeled 8.1-kb DNA is efficiently absorbed by competent Haemophilus cells whereas vector DNA present in the mixture is not, implying that the 8.1-kb DNA contains sequence-specific recognition sites that are needed for DNA uptake. Absorbed DNA can be recovered from cells as a 32P-labeled duplex of unaltered size for several minutes after uptake. We have determined the number and location of uptake sites in the 8.1-kb DNA by constructing a restriction endonuclease cleavage map and assaying fragments for uptake. Only two small fragments retain the ability to be absorbed. These fragments, 120 and 140 base pairs long, are 3.8 kb apart on the 8.1-kb fragment. We assume that each of these fragments contains a short common sequence, perhaps 8--12 base pairs long, that is the actual recognition site. We have shown by DNA competition assays, with the 8.1-kb DNA as a standard, that about 600 copies of the uptake sites are present in the Haemophilus genome.
Complete manifolds with nonnegative scalar curvature and the positive action conjecture in general relativity
Authors: Schoen Richard M. , Yau Shing-Tung
Published: May 2006

We find some integrability conditions for low-dimensional manifolds to admit metrics with nonnegative scalar curvature. In particular, we solve the positive action conjecture in general relativity in the affirmative.
Biochemical assay designed to detect formation of recombination intermediates in vitro.
Authors: Potter H , Dressler D
Published: May 2006

A biochemical assay that is designed to detect recombination intermediates formed in vitro is described. The assay measures the fusion of two essentially homologous plasmids, one of which is radioactively labeled and the other of which carries several copies of the lac operator. The fusion product is radioactive and can be bound to a nitrocellulose filter by lac repressor. This assay for genome fusion is rapid and readily applicable to the many fractions that result during enzyme purification. The fused product is not destroyed in the assay and may be recovered from the filter for further analysis by electron microscopy. The product is then seen to consist of figure 8 structures that can be cleaved by the restriction enzyme EcoRI to give chi forms, structures similar to those recovered from recombination-proficient cells. It is expected that this assay will be useful in the purification of the "recombinase-type" activity detected in crude cell lysates. To demonstrate this point, the assay was applied to the protein fractions recovered from a molecular sieve column. The results indicate that the fusion activity has an apparent molecular weight of 50,000--100,000.
BK virus DNA sequence: extent of homology with simian virus 40 DNA.
Authors: Yang R C , Wu R
Published: May 2006

The primary nucleotide sequence of three regions of BK virus (BKV) variant (MM) DNA has been determined. The region between map positions 0.715 and 0.900 includes the initiation points and partial coding sequences of the putative VP2 and VP3 proteins of BKV(MM), the amino acid sequences of which show over 80% homology with those of VP2 and VP3 of simian virus 40. The sequence of a potential leader protein X, 66 amino acids long for BKV(MM) and 62 long for simian virus 40, is also deduced. The regions between 0.595 and 0.398 and 0.310 and 0.175 include the coding sequence for the entire small t antigen and most of the large T antigen of BKV(MM). The DNA sequence within these regions comprises over 50% of the complete BKV(MM) genome and shows a 70% sequence homology with the corresponding regions of simian virus 40 DNA. This high degree of homology is at variance with the reported homology values of 11--20% estimated by hybridization measurements of heteroduplex analyses. Possible explanations for the discrepancy are discussed.
Genome of avian myelocytomatosis virus MC29: analysis by heteroduplex mapping.
Authors: Hu S S , Lai M M , Vogt P K
Published: May 2006

The virion RNA of avian myelocytoma virus MC29 was hybridized to full genome length DNA of the Prague strain of Rous sarcoma virus and analyzed by heteroduplex mapping in the electron microscopy. The results show that MC29 specific sequences for which there are no homologous counterparts in the Rous sarcoma virus genome make up a contiguous stretch of RNA about 1.8 kilobases long. These sequences are located approximately in the middle of the genome, replacing the 3' half of the gag gene, the entire pol gene, and the 5' portion of the env gene, which are absent from MC29. This MC29 specific genetic substitution may contain information for the leukemogenic transformation of the host cell.
Bird niches in a subalpine forest: An indirect ordination
Authors: Sabo Stephen R. , Whittaker Robert H.
Published: May 2006

Multivariate techniques that are tolerant of the curvilinearity in population responses can be used to ordinate bird species in a niche hyperspace and to quantify niche relationships. Multidimensional scaling, secondary reciprocal averaging, and reciprocal averaging followed by principal components analysis give similar results in an ordination of 20 bird species in a spruce-fir forest. The ordination represents the organization of the bird community in relation to niche axes and suggests grouping of the bird species into guilds. A group of foliage-gleaning insectivores that finely divide their resource base is central to the bird community; other groups of species (ground feeders, aerial feeders, conifer specialists, and bark probers and peckers) have broader niches.
Role of methylation in the modification and restriction of chloroplast DNA in Chlamydomonas.
Authors: Burton W G , Grabowy C T , Sager R
Published: May 2006

The different metabolic paths followed by homologous chloroplast DNAs of maternal and paternal origins in zygotes of Chlamydomonas were examined by prelabeling parental cells, before mating them, with [3H]adenine, [3H]thymidine, and [3H]deoxycytidine. Within 6 hr after mating, maternal chloroplast DNA was extensively methylated to 5-methylcytosine and its bouyant density decreased. Paternal chloroplast DNA was largely degraded. Some radioactivity from deoxycytidine of maternal origin reappeared in thymine, and residual paternal DNA contained radioactivity in a base tentatively identified as uracil. These results confirm and extend our previous findings and support our hypothesis that modification (methylation) and restriction enzymes determine maternal inheritance of chloroplast DNA and that the two parental DNAs have different metabolic fates within the zygote.
Immunocytochemical localization of cyclic GMP: Light and electron microscope evidence for involvement of neuroglia
Authors: Chan-Palay V. , Palay S. L.
Published: May 2006

Guanosine 3′,5′-cyclic monophosphate (cGMP) immunoreactivity in the rat's cerebellum was studied with light and electron microscopy by the indirect fluorescence method and the peroxidase-antiperoxidase method. Labeled cells included neuroglial cells in the cerebellar cortex, white matter, and deep nuclei; some stellate and basket cells in the cortex; and some large neurons in the deep nuclei. No evidence was found for sagittal microzonation in the cGMP distribution. In the labeled cells, cGMP immunoreactive sites were localized to surface membranes, organelles, and the cytoplasmic matrix. Specificity was indicated by the same pattern of labeling after treatment with cGMP immunoglobulin that had been adsorbed with adenosine 3′,5′-cyclic monophosphate (cAMP) and by the failure to label after treatment with normal rabbit sera or with cGMP immunoglobulin that had been adsorbed with 1 mM cGMP. Cerebella treated with cAMP antisera, however, showed immunoreactivity in Purkinje cells, granule cells, and Golgi cells in addition to neuroglia in cortex and deep nuclei. Sequential norepinephrine and glutamate superfusions generally intensified cGMP immunoreactivity, not only in neuroglial cells but also in the background. Under these conditions some Purkinje cells and some granule cells were also labeled. Increased cGMP immunoreactivity was also obtained by treatment with harmaline, γ-aminobutyric acid and aminooxyacetic acid, muscimol, γ-aminobutyric acid, or apomorphine in order of decreasing effectiveness. Serotonin and colchicine produced no detectable increase of cGMP immunoreactivity above normal, and diazepam and sodium pentobarbital decreased it. In these experiments, diethyl ether was preferable to sodium pentobarbital for anesthesia on account of the depressive action of the latter on cGMP immunoreactivity. Thus, drugs that increase cerebellar activity enhance cGMP levels, whereas those that decrease cerebellar activity decrease cGMP levels. However, it is not clear whether these fluctuations in cGMP levels are a direct consequence of neurotransmitter function or are sequelae to other related events. The present study suggests that some neurons and many neuroglial cells are the major sites of cGMP in the cerebellum.
Self-avoiding random walks on lattice strips
Authors: Wall Frederick T. , Klein Douglas J.
Published: May 2006

A self-avoiding walk on an infinitely long lattice strip of finite width will asymptotically exhibit an end-to-end separation proportional to the number of steps. A proof of this proposition is presented together with comments concerning an earlier attempt to deal with the matter. In addition, some unproved, yet “obvious,” conjectures concerning self-avoiding walks are cited as basic propositions requiring study.
Hormonally specific expression of cardiac protein kinase activity
Authors: Hayes J. Scott , Brunton Laurence L. , Brown Joan Heller , Reese James B. , Mayer Steven E.
Published: May 2006

The relationship between the effects of isoproterenol and prostaglandin E
1
(PGE
1
) on contractile state, cyclic AMP accumulation, and the activation states of protein kinase (ATP: protein phosphotransferase, EC 2.7.1.37), phosphorylase kinase, glycogen synthase, and glycogen phosphorylase have been studied in the isolated perfused rat heart. Perfusion of hearts with isoproterenol (10 or 80 nM) caused enhancement of left ventricular
dP/dt
(
P
, pressure), increased intracellular cyclic AMP, increased the activation states of protein kinase, phosphorylase kinase, glycogen phosphorylase, and conversion of glycogen synthase to a less active form. PGE
1
(2 or 30 μM) increased cyclic AMP accumulation and activated protein kinase, but caused no detectable changes in
dP/dt
or the activation states of the protein kinase substrates involved in glycogen metabolism. Perfusion of hearts with either 10 nM isoproterenol or 30 μM PGE
1
produced comparable increases in cyclic AMP accumulation and protein kinase activity. Exposure of hearts to a combination of these agents caused additive effects on cyclic AMP content and protein kinase activity. However, values for phosphorylase kinase, glycogen phosphorylase, glycogen synthase, and
dP/dt
did not differ from those observed in the presence of 10 nM isoproterenol alone. The failure of PGE
1
to stimulate phosphorylation of protein kinase substrates was not due to an increase in phosphorylase phosphatase activity. We conclude that an increase in intracellular cyclic AMP and the subsequent activation of protein kinase are insufficient to change either the activities of phosphorylase kinase, glycogen phosphorylase, and glycogen synthase or the inotropic state of heart muscle.
Evidence for covalent attachment of fatty acids to Sindbis virus glycoproteins.
Authors: Schmidt M F , Bracha M , Schlesinger M J
Published: May 2006

Selective binding of lipid to glycoprotein was detected when [3H]palmitate-labeled Sindbis virus particles or viral-infected cells were disrupted by heating with sodium dodecyl sulfate, and glycoproteins were isolated by electrophoresis in sodium dodecyl sulfate/10% polyacrylamide gels. The smaller glycoprotein (E2) retained 2 to 3 times more labeled lipid than did the larger EI glycoprotein, and the cell-associated glycoprotein precursor (PE2) bound even less lipid. No lipid was associated with the nonglycosylated glycoproteins that accumulated in infected cells treated with tunicamycin. The labeled lipid remained bound to the glycoproteins after exhaustive extraction with chloroform/methanol of virus particles, infected-cell extracts, or isolated glycoproteins, but it could be extracted by chloroform/methanol after treating glycoproteins with mild alkali. Analysis by gas/liquid chromatography showed that 60% of the label was in palmitate and the balance of label was distributed between oleate and stearate. There were approximately 2 mol of fatty acid bound per mol of E1 glycoprotein. Proteolysis of the fatty acid-labeled glycoprotein with pepsin, thermolysin, and Pronase degraded the polypeptide to fragments that retained the fatty acids in an alkali-labile state. These data suggest that a covalent attachment of fatty acid may occur during maturation of the viral glycoproteins.
An Escherichia coli mutant defective in single-strand binding protein is defective in DNA replication.
Authors: Meyer R R , Glassberg J , Kornberg A
Published: May 2006

An Escherichia coli mutant, temperature-sensitive for DNA synthesis in vivo and in vitro, is defective in single-strand binding protein (SSB; DNA-binding protein). Conversion of phage G4 single strands to the duplex form is defective in crude enzyme fractions of the mutant and is complemented by pure wild-type SSB. Radioimmunoassays of mutant extracts show normal levels of material crossreacting with anti-SSB antibody. SSB purified to homogeneity from the mutant is active, with lower specific activity, in the reconstituted G4 replication assay at 30 degrees C, but virtually inactive at 42 degrees C. Surprisingly, the mutant protein, like the wild-type protein, survives heating at 100 degrees C. Thus, mutant SSB is structurally heat-resistant but is functionally thermosensitive in vitro and in vivo. Both the in vivo and in vitro defects are tightly linked in transductions by phage P1. The mutation in the binding protein, designated ssb-1, is located between 90 and 91 min on the E. coli genetic map.
Autotrophic growth of H
2
-uptake-positive strains of
Rhizobium japonicum
in an atmosphere supplied with hydrogen gas
Authors: Hanus F. Joe , Maier Robert J. , Evans Harold J.
Published: May 2006

Previous research from this laboratory has demonstrated CO
2
-fixing and H
2
-uptake capacities of certain strains of
Rhizobium japonicum
. In this report we have shown that SR, a H
2
-uptake-positive (Hup
+
) strain of
R. japonicum
, is capable of autotrophic growth with H
2
as the energy source. Growth occurred on mineral salts/vitamins/Noble agar, mineral salts/vitamins liquid medium (0.27 μg of C as vitamins per ml), and in mineral salts liquid medium with no added vitamins when cultures were provided with NH
4
Cl and incubated in an atmosphere containing H
2
, CO
2
, O
2
, and N
2
. Little or no growth occurred when either H
2
or CO
2
was omitted from the atmosphere or when the culture was inoculated with SR3, a Hup
-
mutant of SR. Growth was measured by protein synthesis, fixed organic carbon, and increase in cell number in liquid cultures. The organism that grew autotrophically was verified as
R. japonicum
by (
i
) apparent purity on streak plates; (
ii
) retention of the double antibiotic resistance markers; and (
iii
) its capability to nodulate soybeans. H
2
- and CO
2
-supported growth was demonstrated for three additional Hup
+
wild-type
R. japonicum
strains (USDA 136, 3I1b 6, and 3I1b 143), while three Hup
-
wild-type strains (USDA 120, 3I1b 144, and USDA 117) were incapable of growth on the Noble agar medium containing mineral salts/vitamins in the H
2
/CO
2
/O
2
/N
2
atmosphere. This demonstrated capability of Hup
+
R. japonicum
strains to grow autotrophically requires revision of current concepts regarding conditions for survival and competition of these bacteria in the soil and their relationships to other microorganisms.
Purification of human platelet-derived growth factor.
Authors: Antoniades H N , Scher C D , Stiles C D
Published: May 2006

Human platelets contain a polypeptide growth factor that stimulates the proliferation of connective tissue cells. Purification of this platelet-derived growth factor (PDGF) was accomplished by heat (100 degrees C) treatment of washed platelets and subsequent ion-exchange chromatography, gel filtration in 1 M acetic acid, isoelectric focusing, and preparative sodium dodecyl sulfate/polyacrylamide gel electrophoresis. PDGF has an isoelectric point of 9.8 and a molecular weight ranging from 13,000 to 16,000 as judged by gel filtration in 1 M acetic acid or analytical sodium dodecyl sulfate gel electrophoresis under reducing conditions. The specific activity of the purified PDGF is 20 million times greater than that found in unfractionated human serum. Purified PDGF stimulates replicative DNA synthesis and cell proliferation in quiescent density-arrested cultures of BALB/c 3T3 cells at concentrations of 1 ng/ml (0.1 nM).
Lateral and vertical displacement of integral membrane proteins during lipid phase transition in Anacystis nidulans.
Authors: Armond P A , Staehelin L A
Published: May 2006

Alterations in membrane structure as a result of lipid phase transitions have been studied in Anacystis nidulans, a blue-green alga. Cells grown at 38 degrees C were subjected to temperature transitions of 38 degrees C leads to 21 degrees C and 38 degrees C leads to 10 degrees C, previously shown to produce substantial changes in photosynthetic activities, and examined by freeze-fracture electron microscopy. As a result of these treatments, large particle-free regions appeared on the fracture faces of both the plasma and thylakoid membranes. Particle density measurements suggest that the displacement of the integral membrane protein complexes occurs in both lateral and vertical directions. Returning the cells to 38 degrees C resulted in the restoration of normal membrane morphology, indicating that the proteins were not lost from the membrane. Such displacement of the integral membrane protein complexes could contribute significantly to the temperature-dependent alterations in the functional activity of membrane-bound enzymatic complexes.
Xylem and nonxylem cell formation in cytokinin-stimulated root tissue: Quantitative analysis of temperature effects
Authors: Shininger Terry L.
Published: May 2006

Xylogenesis in mature root parenchyma is elicited
in vitro
by the concerted action of the hormones cytokinin and auxin. Decreasing the temperature delayed the initiation of xylogenesis relative to the initiation of nonxylem cell formation. Once xylem or nonxylem cell formation was initiated, its rate was not temperature-sensitive within the 10-25°C range. Lowering the temperature after xylem formation had been initiated had little effect on xylem cell formation. Xylogenesis sensitivity to low temperature was demonstrable from the time cultures were established, even though cell division did not occur until 48-72 hr later and overt xylogenesis did not occur until 6 or 7 days later. The cold sensitivity of xylogenesis is not limited to a unique or early phase of culture.
Mutation of the non-Mendelian suppressor, Ψ
+
, in yeast by hypertonic media
Authors: Singh Arjun , Helms Cynthia , Sherman Fred
Published: May 2006

The Ψ
+
extrachromosomal determinant in the yeast
Saccharomyces cerevisiae
suppresses certain UAA markers and increases the efficiency of suppression of UAA suppressors and certain frameshift suppressors. Although the exact nature of Ψ
+
determinant is unknown, it is believed to be a self-replicating cytoplasmic factor affecting some component of the translational machinery. In this report we describe growth conditions for efficient mutation or elimination of the Ψ
+
determinant. Incubation of Ψ
+
cultures in hypertonic nutrient medium resulted in rapid conversion to a culture containing predominantly Ψ
-
cells during the growth cycle. The kinetics of Ψ
+
to Ψ
-
conversion established that the occurrence of Ψ
-
cells was due to induction and not to selection of pre-existing Ψ
-
cells. The results suggest that the replication of the Ψ
+
determinant is sensitive to hypertonic conditions.
Antigen-specific identification and cloning of hybridomas with a fluorescence-activated cell sorter.
Authors: Parks D R , Bryan V M , Oi V T , Herzenberg L A
Published: May 2006

Myeloma-spleen cell hybrids (hybridomas) producing antibody to mouse immunoglobulin allotypes have been labeled with fluorescent microspheres coupled with myeloma protein antigens. The ratio of specific to nonspecific microsphere binding by viable hybridoma cells was about 100:1. By using a modified fluorescence-activated cell sorter (FACS), selected hybridoma cells in a mixture have been sorted individually into media in microculture wells, where, with thymocyte feeder cells, they developed into clones producing a desired monoclonal antibody. Viable cells were selected by measurement of their light scattering and autofluorescence properties. Rare antibody-producing clones were obtained without laborious screening and repeated subculturing. This technique should expand the range of monoclonal antibodies readily obtained from hybridomas and greatly facilitate the process of obtaining desired hybridomas.
Major histocompatibility complex products restrict the adherence of cytolytic T lymphocytes to minor histocompatibility antigens or to trinitrophenyl determinants on schistosomula of Schistosoma mansoni.
Authors: Vadas M A , Butterworth A E , Burakoff S , Sher A
Published: May 2006

We have previously shown that schistosomula passaged through mice acquire histocompatibility (H) antigens that can be recognized either by alloantibody or by alloreactive cytolytic T lymphocytes (CTL). The latter specifically adhere to but fail to damage the parasite. In this paper we describe the use of trinitrophenyl (TNP)-labeled schistosomula to show that the adherence of CTL with specificity for TNP-modified syngeneic cells is restricted by the major histocompatibility complex (MHC) in a fashion similar to that seen in the lysis of TNP-labeled tumor targets. Thus, these CTL adhere only to schistosomula that have both the appropriate H antigens and TNP determinants on their surface, and not to schistosomula bearing either of these antigens by themselves. We note a significant degree of adherence to schistosomula bearing TNP determinants and H antigens allogeneic to the CTL. Anti-minor H antigen CTL are also restricted by the MHC in their adherence; thus, they only adhere to schistosomula that carry both the major and minor H antigens of the stimulator cells. These antigens can be acquired either by a single passage in vivo of schistosomula through congenic strains that possess both the relevant antigens or by sequential passage through two different strains, each contributing one of the antigens in question.
beta-Adrenergic receptor regulation by agonists and membrane depolarization in rat brain slices.
Authors: Wagner H R , Davis J N
Published: May 2006

Rat cerebral cortex slices exposed to (-)-isoproterenol and then washed accumulated significantly less cyclic AMP when rechallenged with isoproterenol than did control slices. The isoproterenol-induced desensitization was associated with a concurrent reduction in [3H]dihydroalprenolol membrane binding but with no change in the affinity of [3H]dihydroalprenolol or isoproterenol for the binding sites. beta-Adrenergic receptor desensitization was rapidly reversed by slice depolarization with high-[K+] buffers, batrachotoxin, grayanotoxin, or veratridine, even in the continued presence of isoproterenol. Restoration of binding by grayanotoxin was prevented by tetrodotoxin or by removing Na+ from the buffer. These data demonstrate partial participation of the membrane receptor in beta-adrenergic desensitization of rat brain slices and suggest that brain beta-adrenergic receptors, like cholinergic receptors in skeletal muscle and alpha-adrenergic receptors in rat parotid, are regulated in part by membrane voltage.
Avermectin B1a irreversibly blocks postsynaptic potentials at the lobster neuromuscular junction by reducing muscle membrane resistance.
Authors: Fritz L C , Wang C C , Gorio A
Published: May 2006

Avermectin B1a, a macrocyclic lactone with broad spectrum anthelmintic activity, affects neuromuscular transmission in the lobster stretcher muscle. Perfusion of the muscle with 1-10 microgram of the drug per ml eliminates inhibitory postsynaptic potentials within a few minutes. Intracellularly recorded excitatory postsynaptic potentials are gradually reduced in amplitude over 20-30 min, and their falling phases become faster; there is no effect, however, on extracellularly recorded excitatory potentials. Avermectin B1a reduced the input resistance of the muscle fibers with a time course similar to that of the reduction of excitatory potentials. Washing for up to 2 hr with drug-free solution fails to reverse the drug's effects. However, perfusion with 20 microgram of picrotoxin per ml results in recovery of the excitatory potentials and input resistance. Avermectin B1a also blocks the firing of the crayfish stretch receptor neuron, and this block is also reversed by picrotoxin. We hypothesize that the reduction in excitatory postsynaptic potentials after avermectin B1a treatment is caused solely by reduction in membrane resistance; additional experiments suggest that the reduction in membrane resistance is due to the opening of membrane Cl- channels, perhaps including those regulated by gamma-aminobutyric acid at the inhibitory synapse.
Arachidonic acid metabolism in polymorphonuclear leukocytes
Authors: Borgeat Pierre , Samuelsson Bengt
Published: May 2006

Addition of arachidonic acid and the divalent cation ionophore A23187 to a suspension of human peripheral blood polymorphonuclear leukocytes led to the formation of (5
S
)-hydroxy-6,8,11,14-icosatetraenoic acid, (15
S
)-hydroxy-5,8,11,13-icosatetraenoic acid, and (5
S
,12
R
)-dihydroxy-6,8,10,14-icosatetraenoic acid. A method based on high-pressure liquid chromatography has been developed for assay of these metabolites. The addition of arachidonic acid to human polymorphonuclear leukocytes always resulted in formation of the isomeric monohydroxy acids. However, cells prepared from blood of different subjects were found to vary with respect to formation of the 5,12-dihydroxy acid. Addition of the ionophore alone strongly stimulated the formation of the 5-monohydroxy acid and more specifically the 5,12-dihydroxy acid from endogenous arachidonic acid. In all experiments performed the formation of the 5-hydroxy acid and the 5,12-dihydroxy acid was maximally stimulated when both arachidonic acid and the ionophore were added to the incubation mixture. Under these conditions, stimulation of 40-fold or more of the formation of both compounds was observed. The data demonstrate that, in addition to causing release of endogenous substrate, the ionophore also activated the enzymatic system involved in the further transformations of arachidonic acid. This finding raises the possibility that this pathway of arachidonic acid metabolism is involved in the biological response (e.g., release of lysosomal enzymes, the slow reacting substance of anaphylaxis, and chemotactic factors) of leukocytes to A23187 and other stimuli.