Showing papers in "Proceedings of the National Academy of Sciences of the United States of America in 1975"
TL;DR: It is proposed that TNF mediates endotoxin-induced tumor necrosis, and that it may be responsible for the suppression of transformed cells by activated macrophages.
Abstract: In studying "hemorrhagic necrosis" of tumors produced by endotoxin, it was found that the serum of bacillus Calmette--Guerin (BCG)-infected mice treated with endotoxin contains a substance (tumor necrosis factor; TNF) which mimics the tumor necrotic action of endotoxin itself. TNF-positive serum is as effective as endotoxin itself in causing necrosis of the sarcoma Meth A and other transplanted tumors. A variety of tests indicate that TNF is not residual endotoxin, but a factor released from host cells, probably macrophages, by endotoxin. Corynebacteria and Zymosan, which like BCG induce hyperplasia of the reticulo-endothelial system, can substitute for BCG in priming mice for release of TNF by endotoxin. TNF is toxic in vitro for two neoplastic cell lines; it is not toxic for mouse embryo cultures. We propose that TNF mediates endotoxin-induced tumor necrosis, and that it may be responsible for the suppression of transformed cells by activated macrophages.
4,490Â citations
TL;DR: There is a high correlation between carcinogenicity and mutagenicity: 90% (156/174) of carcinogens are mutagenic in the test and despite the severe limitations inherent in defining non-carcinogenicity, few "non-Carcinogens" show any degree of mutageniability.
Abstract: About 300 carcinogens and non-carcinogens of a wide variety of chemical types have been tested for mutagenicity in the simple Salmonella/microsome test. The test uses bacteria as sensitive indicators for DNA damage, and mammalian liver extracts for metabolic conversion of carcinogens to their active mutagenic forms. Quantitative mutagenicity data from linear dose-response curves are presented: potency varies over a 10(6)-fold range. There is a high correlation between carcinogenicity and mutagenicity: 90% (156/174) of carcinogens are mutagenic in the test and despite the severe limitations inherent in defining non-carcinogenicity, few "non-carcinogens" show any degree of mutagenicity. The results also demonstrate the great utility, and define the limitations, of the test in detecting environmental carcinogens.
3,181Â citations
TL;DR: This method can be used to isolate clones of ColE1 hybrid plasmids that contain Drosophila melanogaster genes for 18 and 28S rRNAs and any gene whose base sequence is represented in an available RNA.
Abstract: A method has been developed whereby a very large number of colonies of Escherichia coli carrying different hybrid plasmids can be rapidly screened to determine which hybrid plasmids contain a specified DNA sequence or genes. The colonies to be screened are formed on nitrocellulose filters, and, after a reference set of these colonies has been prepared by replica plating, are lysed and their DNA is denatured and fixed to the filter in situ. The resulting DNA-prints of the colonies are then hybridized to a radioactive RNA that defines the sequence or gene of interest, and the result of this hybridization is assayed by autoradiography. Colonies whose DNA-prints exhibit hybridization can then be picked from the reference plate. We have used this method to isolate clones of ColE1 hybrid plasmids that contain Drosophila melanogaster genes for 18 and 28S rRNAs. In principle, the method can be used to isolate any gene whose base sequence is represented in an available RNA.
3,075Â citations
TL;DR: Evidence is presented that the more unstable and major component of rabbit aorta contracting substance (RCS) formed in platelets and guinea pig lung is also thromboxane A2.
Abstract: An unstable [t1/2 at 37 degrees = 32 +/- 2 (SD) sec] intermediate, thromboxane A2, was detected in the conversion of prostaglandin G2 into 8-(1-hydroxy-3-oxopropyl)-9,12L-dihydroxy-5,10-heptadecadienoic acid (thromboxane B2) in platelets. The intermediate was trapped by addition of methanol, ethanol, or sodium azide to suspensions of washed human platelets incubated for 30 sec with arachidonic acid or prostaglandin G2. The structures of the resulting derivatives demonstrated that the intermediate possessed an oxane ring as in thromboxane B2 but lacked its hemiacetal hydroxyl group. Additional experiments using 18O2 or [2H8]arachidonic acid in the formation of thromboxane B2 and CH3O2H for the trapping of thromboxane A2, together with information on the t1/2 of the intermediate, indicated the presence of an oxetane structure in thromboxane A2. Incubation of arachidonic acid or prostaglandin G2 with washed platelets led to formation of an unstable factor that induced irreversible platelet aggregation and caused release of [14C]serotonin from platelets that had been incubated with [14C]serotonin. The properties and the mode of formation of this factor indicated that it was identical with thromboxane A2. Furthermore, evidence is presented that the more unstable and major component of rabbit aorta contracting substance (RCS) formed in platelets and guinea pig lung is also thromboxane A2.
2,776Â citations
TL;DR: The unique ability of tau to restore the normal features of in vitro microtubules assembly makes it likely that tau is a major regulator of microtubule formation in cells.
Abstract: A heat stable protein essentail for microtubule assembly has been isolated. This protein, which we designate tau (tau), is present in association with tubulin purified from porcine brain by repeated cycles of polymerization. Tau is separated from tubulin by ion exchange chromatography on phosphocellulose. In the absence of tau, tubulin exists entirely as a 6S dimer of two polypeptide chains (alpha and beta tubulin) with a molecular weight of 120,000, which will not assemble into microtubules in vitro. Addition of tau completely restores tubule-forming capacity. Under nonpolymerizing conditions, tau converts 6S dimers to 36S rings-structures which have been implicated as intermediates in tubule formation. Hence, tau appears to act on the 6S tubulin dimer, activating it for polymerization. The unique ability of tau to restore the normal features of in vitro microtubule assembly makes it likely that tau is a major regulator of microtubule formation in cells.
2,703Â citations
TL;DR: The sequence of 72 base pairs of the rightward operator (O-R) of bacteriophage lambda is presented as determined with simple and rapid methods for direct DNA sequencing and three sites recognized by the lambda phage repressor are identified.
Abstract: The sequence of 72 base pairs of the rightward operator (O-R) of bacteriophage lambda is presented as determined with simple and rapid methods for direct DNA sequencing The sequence of an operator mutant is also described The methods are of general use in sequencing DNA fragments with unique 5' ends up to 50 base pairs in length Previous experiments have shown that this operator contains multiple sites recognized by the lambda phage repressor We believe we have identified three of these sites
1,628Â citations
TL;DR: It is suggested that for a realistic situation translational diffusion should be about four times faster in relation to rotational diffusion than in the isotropic case.
Abstract: Brownian motion (diffusion) of particles in membranes occurs in a highly anisotropic environment. For such particles a translational mobility (independent of velocity) can be defined if the viscosity of the liquid embedding the membrane is taken into account. The results of a model calculation are presented. They suggest that for a realistic situation translational diffusion should be about four times faster in relation to rotational diffusion than in the isotropic case.
1,611Â citations
TL;DR: After almost 200 transplant generations as a highly malignant tumor, embryoid body core cells appear to be developmentally totipotent and able to express, in an orderly sequence in differentiation of somatic and germ-line tissues, many genes hitherto silent in the tumor of origin.
Abstract: Malignant mouse teratocarcinoma (or embryonal carcinoma) cells with a normal modal chromosome number were taken from the "cores" of embryoid bodies grown only in vivo as an ascites tumor for 8 years, and were injected into blastocysts bearing many genetic markers, in order to test the developmental capacities, genetic constitution, and reversibility of malignancy of the core cells. Ninety-three live normal pre- and postnatal animals were obtained. Of 14 thus far analyzed, three were cellular genetic mosaics with substantial contributions of tumor-derived cells in many developmentally unrelated tissues, including some never seen in the solid tumors that form in transplant hosts. The tissues functioned normally and synthesized their specific products (e.g., immunoglobulins, adult hemoglobin, liver proteins) coded for by strain-type alleles at known loci. In addition, a tumor-contributed color gene, steel, not previously known to be present in the carcinoma cells, was detected from the coat phenotype. Cells derived from the carcinoma, which is of X/Y sex chromosome constitution, also contributed to the germ line and formed reproductively functional sperms, some of which transmitted the steel gene to the progeny. Thus, after almost 200 transplant generations as a highly malignant tumor, embryoid body core cells appear to be developmentally totipotent and able to express, in an orderly sequence in differentiation of somatic and germ-line tissues, many genes hitherto silent in the tumor of origin. This experimental system of "cycling" teratocarcinoma core cells through mice, in conjunction with experimental mutagenesis of those cells, may therefore provide a new and useful tool for biochemical, developmental, and genetic analyses of mammalian differentiation. The results also furnish an unequivocal example in animals of a non-mutational basis for transformation to malignancy and of reversal to normalcy. The origin of this tumor from a disorganized embryo suggests that malignancies of some other, more specialized, stem cells might arise comparably through tissue disorganization, leading to developmental aberrations of gene expression rather than changes in gene structure.
1,059Â citations
TL;DR: A simple model shows that within organisms possessing a dispersal phase the processes of mating, competition, feeding, and predation are often carried out within "trait-groups," defined as populations enclosed in areas smaller than the boundaries of the deme.
Abstract: In organisms possessing a dispersal phase the processes of mating, competition, feeding, and predation are often carried out within "trait-groups," defined as populations enclosed in areas smaller than the boundaries of the deme. A simple model shows that this can lead to the selection of "altruistic" traits that favor the fitness of the group over that of the individual. The extent of group selection that occurs depends mainly on the variation in the composition of genotypes between trait-groups. The traditional concepts of group and individual selection are seen as two extremes of a continuum, with systems in nature operating over the interval in between.
1,058Â citations
TL;DR: The utility of a simple test on petri plates for detecting chemical carcinogens as mutagens is extended by introducing two new bacterial strains which can detect with great sensitivity many carcinogens which it did not detect before or detected with less sensitivity.
Abstract: We described previously a simple test on petri plates for detecting chemical carcinogens as mutagens, using an especially sensitive set of bacterial strains to detect mutagenic acitivty and a mammalian liver extract for carcinogen activity. We now extend the utility of the method by introducing two new bacterial strains which can detect with great sensitivity many carcinogens which we did not detect before or detected with less sensitivity. Among these carcinogens are aflatoxin B-1, sterigmatocystin, benzyl chloride, benzo[a]-pyrene, 7,12-dimethylbenzanthracene, 1'-acetoxysafrole, and the nitrofuran food additive furylfuramide (AF-2). The new strains TA100 and TA98 contain an R factor plasmid, pKM101, in our standard tester strains TA1535 and TA1538. The R factor increases mutagenesis with certain mutagens, but not others. We present evidence that the mutagens that become more effective work through an error-prone recombinational repair.
984Â citations
TL;DR: Evidence is presented that penicillin bulge formation is due to the inhibition of proteins 2 and 3 in the absence of inhibition of protein 1.
Abstract: The varied effects of beta-lactam antibiotics on cell division, cell elongation, and cell shape in E. coli are shown to be due to the presence of three essential penicillin binding proteins with distinct roles in these three processes. (A) Cell shape: beta-Lactams that specifically result in the production of ovoid cells bind to penicillin binding protein 2 (molecular weight 66,000). A mutant has been isolated that fails to bind beta-lactams to protein 2, and that grows as round cells. (B) Cell division: beta-Lactams that specifically inhibit cell division bind preferentially to penicillin binding protein 3 (molecular weight 60,000). A temperature-sensitive cell division mutant has been shown to have a thermolabile protein 3. (C) Cell elongation: One beta-lactam that preferentially inhibits cell elongation and causes cell lysis binds preferentially to binding protein 1 (molecular weight 91,000). Evidence is presented that penicillin bulge formation is due to the inhibition of proteins 2 and 3 in the absence of inhibition of protein 1.
TL;DR: The results suggest that aspirin acts as an active-site acetylating agent for the enzyme cyclo-oxygenase, which may account for its anti-inflammatory and anti-platelet action.
Abstract: When microsomes of sheep or bovine seminal vesicles are incubated with [acetyl-3H]aspirin (acetyl salicylic acid), 200 Ci/mol, we observe acetylation of a single protein, as measured by sodium dodecyl sulfate/polyacrylamide gel electrophoresis. The protein has a molecular weight of 85,000 and corresponds to a similar acetylated protein found in the particulate fraction of aspirin-treated human platelets. The aspirin-mediated acetylation reaction proceeds with the same time course and at the same concentration as does the inhibition of prostaglandin synthase (cyclo-oxygenase) (EC 1.14.99.1; 8,11,14-eicosatrienoate, hydrogen-donor:oxygen oxidoreductase) by the drug. At 100 muM aspirin, 50% inhibition of prostaglandin synthase and 50% of maximal acetylation are observed after 15 min at 37 degrees. Furthermore, the substrate for cyclo-oxygenase, arachidonic acid, inhibits protein acetylation by aspirin at concentrations (50% inhibition at 10-30 muM) which correlate with the Michaelis constant of arachidonic acid as a substrate for cyclooxygenase. Arachidonic acid analogues and indomethacin inhibit the acetylation reaction in proportion to their effectiveness as cyclo-oxygenase inhibitors. The results suggest that aspirin acts as an active-site acetylating agent for the enzyme cyclo-oxygenase. This action of aspirin may account for its anti-inflammatory and anti-platelet action.
TL;DR: The results suggest that sperm abnormalities might provide a rapid inexpensive mammalian screen for agents that lead to errors in the differentiation of spermatogenic stem cells in vivo and thus indicate agents which might prove to be mutagenic, teratogenic, or carcinogenic.
Abstract: The sperm of (C57BL X C3H)F1 mice were examined 1, 4, and 10 weeks after a subacute treatment with one of 25 chemicals at two or more dose levels. The fraction of sperm that were abnormal in shape was elevated above control values of 1.2-3.4% for methyl methanesulfonate, ethyl methanesulfonate, griseofulvin, benzo[a]pyrene, METEPA [tris(2-methyl-l-aziridinyl)phosphine oxide], THIO-TEPA [tris(l-aziridinyl)phosphine sulfide], mitomycin C, myleran, vinblastine sulphate, hydroxyurea, 3-methylcholanthrene, colchicine, actinomycin D, imuran, cyclophosphamide, 5-iododeoxyuridine, dichlorvos, aminopterin, and trimethylphosphate. Dimethylnitrosamine, urethane, DDT [1,1,1-trichloro-2,2-bis(p-chlorophenyl)ethane], 1,1-dimethylhydrazine, caffeine, and calcium cyclamate did not induce elevated levels of sperm abnormalities. The results suggest that sperm abnormalities might provide a rapid inexpensive mammalian screen for agents that lead to errors in the differentiation of spermatogenic stem cells in vivo and thus indicate agents which might prove to be mutagenic, teratogenic, or carcinogenic.
TL;DR: Given a well-behaved real function Y of a real random variable X and the first two or three moments of X, expressions are derived for the moments of Y as linear combinations of powers of the point estimates y(x(+)) and y (x(-)), where x(+) and x(-) are specific values of X.
Abstract: Given a well-behaved real function Y of a real random variable X and the first two or three moments of X, expressions are derived for the moments of Y as linear combinations of powers of the point estimates y(x+) and y(x-), where x+ and x- are specific values of X Higher-order approximations and approximations for discontinuous Y using more point estimates are also given Second-moment approximations are generalized to the case when Y is a function of several variables
TL;DR: Di- and tripeptides containing formylmethionine are strong attractants for both neutrophils and macrophages, whereas the corresponding nonacylated compounds are not chemotactic.
Abstract: Leucocytes such as neutrophils are attracted by N-formylmethionine, but not by methionine. Di- and tripeptides containing formylmethionine are strong attractants for both neutrophils and macrophages, whereas the corresponding nonacylated compounds are not chemotactic. The formylated peptides may be related to an incompletely characterized chemotactic material normally produced by bacteria which attract the same animal cells.
TL;DR: A general model is proposed for genetic recombination, which proposes the hypothesis that recombination is initiated by a single-strand (or asymmetric) transfer, which may, after isomerization, become a two-stranded exchange.
Abstract: A general model is proposed for genetic recombination. Its essential new feature is the hypothesis that recombination is initiated by a single-strand (or asymmetric) transfer, which may, after isomerization, become a two-strand (or symmetric) exchange. The likelihood of this transition from asymmetric to symmetric strand exchange determines certain characteristic features of recombination in any particular organism.
TL;DR: Results suggest that the single cellular property consistently associated with tumorigenicity in nude mice is the acquisition by virus-transformed cells of the ability to proliferate in vitro in the absence of anchorage.
Abstract: Clonal isolates of mouse 3T3 cells and primary rat embryo cells, recovered nonselectively after infection by simian virus 40 (SV40), have been tested for tumorigenicity in the immune-deficient nude mice in order to determine the cellular growth properties in vitro specifically correlated with neoplastic growth in vivo. In addition, mouse 3T3 cells transformed by murine sarcoma virus (MuSV, Kirsten strain), and revertants isolated from cells fully transformed by either SV40 or MuSV were also studied. Results suggest that the single cellular property consistently associated with tumorigenicity in nude mice is the acquisition by virus-transformed cells of the ability to proliferate in vitro in the absence of anchorage. Other cellular parameters of virus-induced transformation, such as lack of sensitivity to high cell density and the capacity to grow in low serum concentration, are dissociable from cellular tumorigeneicity. This conclusion is supported further by the demonstration that specific selection in vivo for tumorigenic cells from anchorage-dependent cells results in the isolation of anchorage-independent cells. Conversely, a single-step selection in vitro for anchorage-independent cells from nontumorigenic cells results in a simultaneous selection of highly tumorigenic subclones.
TL;DR: The relationship between the net and the crude probabilities of survival was established by Therorems 1 and 2 as mentioned in this paper, which showed that, without the not directly verifiable assumption that in their joint distribution the variables Y1, Y2,..., Yk are mutually independent, a given set of crude survival probabilities Qi(t) does not identify the corresponding net probabilities.
Abstract: For an experimental animal exposed to k greater than 1 possible risks of death R1, R2, ..., Rk, the term i-th potential survival time designates a random variable Yi supposed to represent the age at death of the animal in hypothetical conditions in which Ri is the only possible risk. The probability that Yi will exceed a preassigned t is called the i-th net survival probability. The results of a survival experiment are represented by k "crude" survival functions, empirical counterparts of the probabilities Qi(t) that an animal will survive at least up to the age t and eventually die from Ri. The analysis of a survival experiment aims at estimating the k net survival probabilities using the empirical data on those termed crude. Therorems 1 and 2 establish the relationship between the net and the crude probabilities of survival. In particular, Theorem 2 shows that, without the not directly verifiable assumption that in their joint distribution the variables Y1, Y2, ..., Yk are mutually independent, a given set of crude survival probabilities Qi(t) does not identify the corresponding net probabilities. An example shows that the results of a customary method of analysis, based on the assumption that Y1, Y2, ..., Yk are independent, may have no resemblance to reality.
TL;DR: There are similarities between the process of embryoid body formation and the early events of differentiation of the mouse embryo in vitro, and extensive differentiation to a wide variety of cell types occurs.
Abstract: The differentiation in vitro of clonal pluripotent teratocarcinoma cells is reported. The first stage of this process is the formation of simple embryoid bodies which are identical to those found in animals bearing intraperitoneal teratocarcinomas. They consist of an inner core of embryonal carcinoma cells surrounded by a layer of endodermal cells which produce Reichert's membrane. The endodermal cells become apparent shortly after the embryonal carcinoma cells have formed aggregates which are loosely attached to the substratum. One clonal teratocarcinoma line was found to produce complex cystic embryoid bodies in vitro. Following formation of the endodermal cells, extensive differentiation to a wide variety of cell types occurs. There are similarities between the process of embryoid body formation and the early events of differentiation of the mouse embryo.
TL;DR: These findings may implicate vitamin K metabolism in normal bone development and suggest a role for the gamma-carboxyglutamate-rich protein in regulation of calcium salt deposition in mineralized tissues.
Abstract: A direct approach has been developed for quantitative identification of the calcium-binding amino acid, gamma-carboxyglutamate, in proteins. This should be advantageous for the study of numerous systems where specific roles for the binding of calcium or other divalent cations are suspected. Investigation of mineralized tissue, where calcium-binding proteins are implicated in the mineralization process, revealed that gamma-carboxyglutamate was present in proteins solubilized from chicken bone with neutral aqueous ethylenediamine tetraacetic acid. This was established by direct isolation of the amino acid from alkaline hydrolysates and its quantitative conversion to glutamic acid by decarboxylation in 0.05 M HCl at 100 degrees. The kinetics of decarboxylation and chromatographic behavior are identical to those of gamma-carboxyglutamate from human prothrombin. After resolution of the soluble bone proteins by phosphate gradient elution from hydroxyapatite, gamma-carboxyglutamate was found to be concentrated primarily in one BaSO4-adsorbable anionic protein species; bone collagen was devoid of the amino acid. In view of the recently discovered requirement of vitamin K for generation of calcium binding sites (gamma-carboxyglutamate) by gamma-carboxylation of specific glutamic acid residues in prothrombin, our findings may implicate vitamin K metabolism in normal bone development and suggest a role for the gamma-carboxyglutamate-rich protein in regulation of calcium salt deposition in mineralized tissues.
TL;DR: Various antipsychotic drugs inhibited this stereospecific component in both the dopamine and haloperidol assays, and these inhibitory potencies correlated with the clinical doses used for controlling schizophrenia.
Abstract: In order to test the suggestion that antipsychotic drugs act by blocking dopamine receptors in the brain, the direct effects of such neuroleptic drugs were tested on the stereospecific binding of [3H]dopamine and of [3H]haloperidol to rat brain striata and their subfractions. The stereospecific component of binding was defined as that amount of [3h]dopamine or [3H]haloperidol bound in the presence of (-)-butaclamol (an inactive drug) minus that bound in the presence of (+)-butaclamol (a potent neuroleptic drug); 100 nM butaclamol was used for the [3H]haloperidol assay, while 1 muM butaclamol was used for the [3H]dopamine assay. Various antipsychotic drugs inhibited this stereospecific component in both the dopamine and haloperidol assays. These inhibitory potencies correlated with the clinical doses used for controlling schizophrenia.
TL;DR: This polypeptide shows a high degree of evolutionary conservation, exhibiting close structural, functional, and immunological similarity when isolated from such diverse origins as cells of mammals and higher plants, and so may well be a universal constituent of living cells.
Abstract: A polypeptide of 8500 molecular weight is described that induces the differentiation of T (thymus-derived) cell and B (bone-marrow-derived) cell immunocytes in vitro, apparently via beta-adrenergic receptors and adenylate cyclase activation. This polypeptide shows a high degree of evolutionary conservation, exhibiting close structural, functional, and immunological similarity when isolated from such diverse origins as cells of mammals and higher plants. This polypeptide was detected in animal cells, yeast, bacteria, and higher plants, and so may well be a universal constituent of living cells.
TL;DR: The results suggest that the mouse blastocyst is not permeable for certain antibodies, and the inner cell masses can easily be separated from the remnants of trophoblastic cells and are then able to grow and differentiate in vitro.
Abstract: Mouse blastocysts with and without zonae pellucidae are susceptible to complement-dependent antibody cytotoxicity. Exposure of blastocysts to rabbit anti-mouse serum together with complement results in the death of all cells; however, when blastocysts are exposed to antiserum alone and then transferred to guinea pig complement, only the trophoblastic cells are killed. These results suggest that the mouse blastocyst is not permeable for certain antibodies. The inner cell masses can easily be separated from the remnants of trophoblastic cells and are then able to grow and differentiate in vitro. This method of immunosurgery can be used to obtain large quantities of pure inner cell masses in a relatively short period of time.
TL;DR: The coupled inhibitory and positive regulatory mechanisms for adenylate cyclase provide a means of activating and deactivating neural circuits hours after the initial event and thus may play a role in a memory process.
Abstract: Narcotics affect adenylate cyclase [ATP pyrophosphate-lyase (cyclizing), EC 4.6.1.1] in two opposing ways, both mediated by the opiate receptor. The first process is the readily reversible inhibition of the enzyme by narcotics; the second is a compensatory increase in enzyme activity which is delayed in onset and relatively stable. Late positive regulation of the enzyme counteracts the inhibitory influence of morphine and is responsible for narcotic dependence and tolerance. The coupled inhibitory and positive regulatory mechanisms for adenylate cyclase provide a means of activating and deactivating neural circuits hours after the initial event and thus may play a role in a memory process.
TL;DR: O-Phthalaldehyde, in the presence of 2-mercaptoethanol, reacts with primary amines to form highly fluorescent products that can be detected easily and soluble and stable in aqueous buffers.
Abstract: O-Phthalaldehyde, in the presence of 2-mercaptoethanol, reacts with primary amines to form highly fluorescent products. Picomole quantities of amino acids, peptides, and proteins can be detected easily. o-Phthalaldehyde is five to ten times more sensitive than fluorescamine and is soluble and stable in aqueous buffers.
TL;DR: Crosslinking with dimethyl suberimidate reveals a chain of histone octamers in chromatin that can be isolated free in solution at high ionic strength and pH.
Abstract: Crosslinking with dimethyl suberimidate reveals a chain of histone octamers in chromatin. The octamer can be isolated free in solution at high ionic strength and pH. The identification of dimers formed by crosslinking reveals two or more contacts of each histone with others within the octamer. The molecular weight (110,000) and pattern of dissociation of the octamer are compatible with the composition (F2A1)2(F3)2(F2A2)2(F2B)2.
TL;DR: Two cell lines from classes of xeroderma pigmentosum that are defective in excision-repair show intermediate effects, with regard to both the time taken to convert newly synthesized DNA to high molecular weight and the inhibition of this process by caffeine.
Abstract: Cells cultured from most patients suffering from the sunlight-sensitive hereditary disorder xeroderma pigmentosum are defective in the ability to excise ultraviolet light (UV)-induced pyrimidine dimers from their DNA. There is, however, one class of these patients whose cells are completely normal in this excision repair process. We have found that these cells have an abnormality in the manner in which DNA is synthesized after UV-irradiation. The time taken to convert initially low-molecular-weight DNA synthesized in UV-irradiated cells into high-molecular-weight DNA similar in size to that in untreated cells is much greater in these variants than in normal cells. Furthermore, this slow conversion of low to high-molecular-weight newly synthesized DNA is drastically inhibited by caffeine, which has no effect in normal cells. Two cell lines from classes of xeroderma pigmentosum that are defective in excision-repair show intermediate effects, with regard to both the time taken to convert newly synthesized DNA to high molecular weight and the inhibition of this process by caffeine.
TL;DR: Pseudomonas aeruginosa toxin (PA toxin) inhibits protein synthesis in a reticulocyte cell-free system as discussed by the authors, which results in a block at an elongation step of polypeptide assembly.
Abstract: Pseudomonas aeruginosa toxin (PA toxin) inhibits protein synthesis in a reticulocyte cell-free system. The inhibition requires NAD and results in a block at an elongation step of polypeptide assembly. PA toxin was found to act like diphtheria toxin fragment A. Both toxins catalyze the transfer of radioactivity from nicotinamide(U-14-C)adenine dinucleotide ((14-C)NAD) into covalent linkage with the 100,000 dalton elongation (EF-2) protein. Furthermore, in the presence of a limiting amount of EF-2, excess toxin, and (14-C)NAD, the two toxins were non-additive in the amount of label transferred to EF-3. Unlike free fragment A of diphtheria toxin, the enzymatic activity of PA toxin is heat labile and neutralizable with antibody to PA toxin but not with antibody to fragment A. Although PA and diphtheria toxins have different cellular specificities and molecular properties and produce different clinical symptoms, their intracellular mechanisms of action appear to be identical.
TL;DR: The data indicate that the on and off controls inherent in the cascade regulation of viral polypeptide synthesis are mediated by one or morepolypeptides in each group at transcriptional or post-transcriptional levels.
Abstract: It was previously shown that virus-specific polypeptides made in HEp-2 cells infected with herpes simplex 1 form three groups designated alpha, beta, and gamma whose synthesis is coordinately regulated and sequentially ordered. This report shows that one or more functional alpha polypeptides are necessary to turn on the synthesis of beta and gamma groups, and conversely, one or more polypeptides in the latter groups turn off the synthesis of alpha polypeptides. Specifically, infected cells maintained in medium containing either canavanine, an analogue of arginine, or azetidine-2-carboxylic acid an analogue of proline and hydroxyproline, synthesized alpha polypeptide at rates comparable to maximal rates in untreated infected cells but did not undergo the normal transition to beta and gamma polypeptide synthesis. The transition to gamma polypeptide synthesis and shut-off of synthesis of earlier polypeptide groups proceeded normally if addition of canavanine was delayed until at least 4-5 hr after infection. Addition of canavanine after the onset of beta and gamma polypeptide synthesis, i.e., between 2 and 3.5 hr after infection, resulted in sustained, simultaneous synthesis of all three polypeptide groups, a phenomenon not seen in untreated infected cells. Canavanine-treated infected cells, synthesizing alpha polypeptides, recovered the capacity to make beta and gamma polypeptides after removal of the analogue, but only after a 1-to 2-hr delay compared with infected untreated cells. The data indicate that the on and off controls inherent in the cascade regulation of viral polypeptide synthesis are mediated by one or more polypeptides in each group at transcriptional or post-transcriptional levels.
TL;DR: Rates of speciation can be estimated for living taxa by means of the equation for exponential increase, and are clearly higher for mammals than for bivalve mollusks.
Abstract: Gradual evolutionary change by natural selection operates so slowly within established species that it cannot account for the major features of evolution. Evolutionary change tends to be concentrated within speciation events. The direction of transpecific evolution is determined by the process of species selection, which is analogous to natural selection but acts upon species within higher taxa rather than upon individuals within populations. Species selection operates on variation provided by the largely random process of speciation and favors species that speciate at high rates or survive for long periods and therefore tend to leave many daughter species. Rates of speciation can be estimated for living taxa by means of the equation for exponential increase, and are clearly higher for mammals than for bivalve mollusks.