bluuebunny/crossref_metadata_2025 huggingface dataset:
Early effect of interferon on mouse leukemia cells cultivated in a chemostat.
Authors: Tovey M , Brouty-Boyé D , Gresser I
Published: May 2006

Mouse interferon preparations inhibited the multiplication of mouse leukemia L 1210 cells cultivated under steady-state conditions in a chemostat. The use of this sensitive and controlled system led to the detection of a rapid inhibition in the incorporation of (3-H)thymidine into cellular acid-precipitable material 2 hr after the addition of interferon, whereas an effect on cell multiplication was not detected until 22 hr later. Interferon exerted only a transitory effect on the incorporation of (3-H)uridine into acid-precipitable material and no effect on the incorporation of 14-C-amino acids into cellular protein. It is suggested that the chemostat offers many advantages for the investigation of those physiologic factors or chemotherapeutic substances that modify cell division.
Specific binding of tryptophan transfer RNA to avian myeloblastosis virus RNA-dependent DNA polymerase (reverse transcriptase).
Authors: Panet A , Haseltine W A , Baltimore D , Peters G , Harada F , Dahlberg J E
Published: May 2006

The ability of tryptophan tRNA (tRNATrp) to initiate reverse transcription of the 70S RNA of avian RNA tumor viruses suggested that the reverse transcriptase (RNA-dependent DNA polymerase; deoxynucleosidetriphosphate: DNA deoxynucleotidyltransferase; EC 2.7.7.7) might have a specific binding site for the tRNA. A complex of tRNATrp and the avian myeloblastosis virus reverse transcriptase has been demonstrated using chromatography on Sephadex G-100 columns. Of all the chicken tRNAs, only tRNATrp and a tRNA4Met bind to the enzyme with high enough affinity to be selected from a mixture of the chicken cell tRNAs. The ability of tRNATrp to change the sedimentation rate of the enzyme indicates that tRNATrp is not binding to a contaminant in the enzyme preparation. Treatment of the enzyme with monospecific antibody to reverse transcriptase prevented binding of tRNA as well as inhibited the DNA polymerase activity of the enzyme. The ability of reverse transcriptase to utilize tRNATrp aa a primer for DNA synthesis, therefore, appears to involve a highly specific site on the enzyme.
Site-specific cleavage of single-stranded DNA by a Hemophilus restriction endonuclease.
Authors: Horiuchi K , Zinder N D
Published: May 2006

Single-stranded viral DNA of bacteriophage f1 is cleaved into specific fragments by endo R-HaeIII, a restriction endonuclease isolated from Hemophilus aegyptius. The sites of the single strand cleavage correspond to those of the double strand cleavage. A single-stranded DNA fragment containing only one HaeIII site is also cleaved by this enzyme. This observation suggests that the reaction of single-stranded DNA cleavage does not require the formation of a symmetrical double-stranded structure that would result from the intramolecular base-pairing between two different HaeIII sites. Other restriction endonucleases may also cleave single-stranded DNA.
New chromosomal location for structural genes of ribosomal proteins.
Authors: Watson R J , Parker J , Fiil N P , Flaks J G , Friesen J D
Published: May 2006

An Escherichia coli mutant, ts9, previously reported by Flaks et al. (Cold Spring Harbor Symp. Quant. Biol. 31, 623-631, 1966) to have an electrophoretically altered ribosomal protein, has been further characterized and the altered component has been identified as L7/L12. Although mutant ts9 is temperature sensitive for growth (rts-), the rts and L7/L12 mutations are genetically separable and are both located between argH and rif. The L7/L12 mutation (rpyL) maps very close to relC, mutants of which have a defect in the 50S ribosomal subunit. The gene order is argH-rts-(rpyL,relC)-rif. Protein synthesis directed by bacteriophage lambdacI857S7drifd18 in ultraviolet-irradiated cells indicates that L7/L12, As well as L1, L10, L11, and possibly L8 or L9 are coded by the phage DNA. Our results indicate that rpyL is the structural gene for L7/L12 and that this region of the E. coli chromosome contains a cluster of structural genes for ribosomal proteins.
Bidirectional replication of plasmid R6K DNA in Escherichia coli; correspondence between origin of replication and position of single-strand break in relaxed complex.
Authors: Lovett M A , Sparks R B , Helinski D R
Published: May 2006

Replicating molecules of plasmid R6K DNA have been purified as covalently closed circular DNA forms and analyzed in the electron microscopy after cleavage with the EcoRI restriction endonuclease. It has been determined that in most cases replication proceeds bidirectionally from an origin whose position is indistinguishable from the site of the single-strand break (nick) in the open circular DNA form of the relaxation complex of R6K DNA and protein. Evidence is presented for the existence of a unique replication terminus asymmetrically placed approximately 20% of genome size from the origin. The positions of the replication forks in a majority of the molecules indicate that replication proceeds sequentially from the fixed origin first in one direction to the terminus and then progresses from the origin in the other direction.
ATP, cyclic AMP, and magnesium increase the affinity of rat striatal tyrosine hydroxylase for its cofactor.
Authors: Lovenberg W , Bruckwick E A , Hanbauer I
Published: May 2006

Treatment of rat striatal tyrosine hydroxylase [tyrosine 3-monooxygenase; L-tyrosine, tetrahydropteridine:oxygen oxidoreductase (3-hydroxylating); EC 1.14.16.2] with conditions optimal for protein phosphorylation results in the reduction of the tyrosine hydroxylase Km for the cofactor 6-methyltetrahydropterin from 0.50 mM to 0.16 mM. This reaction is dependent upon ATP, 3':5'-cAMP, and Mg++ and causes a marked decrease in the sensitivity to end-product inhibition. Other brain regions and the adrenal gland show a similar response.
Effect of chemical inactivating agents on glucocorticoid receptor proteins in mouse and hamster cells.
Authors: Young H A , Parks W P , Scolnick E M
Published: May 2006

The ffect of N-ethylmaleimide and iodoacetamide on the glucocorticoid receptor activity extracted from the cytosol of either mouse of hamster cells has been investigated. Treatment of mouse or hamster cytosol with N-ethylmaleimide or iodoacetamide rapidly inactivates the [3H]glucocorticoid hormone binding activity of either cytosol. Prebinding the glucocorticoid hormone, dexamethasone, to the cytosol receptor blocks the rapid inactivation of the receptor by N-ethylmaleimide. Treatment of the prebound hormone-receptor complex with iodoacetamide prevents the subsequent binding of the hormone-receptor complex to DNA without causing a dissociation of the complex. Although the conclusions may be limited by the lack of purity of the receptor, the results suggest that a sulfhydryl group is involved in the binding of glucocorticoid hormones to the receptor protein. In addition, the results suggest that iodoacetamide is inactivating a separate chemical site which is necessary for the binding of the hormone-receptor complex to DNA.
Electron microscopy of meiosis in
Drosophila melanogaster
females: II: The recombination nodule—a recombination-associated structure at pachytene?
Authors: Carpenter Adelaide T. C.
Published: May 2006

The recombination nodule is a transient structure present during pachytene in intimate association with the synaptonemal complex. The total numbers of these structures per nucleus and their locations along the bivalents correspond to the total numbers and distributions of genetic exchanges. It is suggested that this structure may be involved in the recombination process.
C-type virus particles in placenta of normal healthy Sprague-Dawley rats.
Authors: Gross L , Schidlovsky G , Feldman D , Dreyfuss Y , Moore L A
Published: May 2006

C-type virus particles were found on electron-microscopic examination in placentas from two out of four young healthy Sprague-Dawley rats. One of these specimens contained virus particles budding from the plasma membranes of cells in the junctional zone of the placenta, i.e., the region where the fetal and maternal cell layers meet. In the other placenta, immature and mature C-type virus particles were found among cell debris also in the junctional region. This observation adds another species of animals to those recently reported, such as rhesus and baboon monkeys, as well as humans, in which C-type virus particles were found in the placenta. The presence of C-type viicant in view of the fact that a considerable number of these animals develop spontaneously a variety of malignant tumors, occasionally also leukemia and malignant lymphomas; however, none of these spontaneous tumors reveals the presence of virus particles on electron-microscopic examination. The nature of virus particles detected in rat placenta remains to be determined. As a working hypothesis, it is possible to assume that they may represent the passage of latent, presumably oncogenic, viruses transmitted "vertically" from parents to offspring. In the course of this passage some of them may be formed, emerging temporarily from their latency, before losing their identity and being again incorporated into the cell genetic components.
Aggression patterns and speciation.
Authors: Nevo E , Naftali G , Guttman R
Published: May 2006

The evolutionary significance of interspecific aggression as a factor in speciation was tested among three chromosome forms of the actively speciating fossorial rodent Spalax ehrenbergi in Israel. Laboratory experiments testing intra- and interspecific aggression were conducted on 48 adult animals from 10 populations comprising three chromosome forms with 2n = 52, 58, and 60. Twelve agonistic, motivational-conflict, and territorial behavioral variables were recorded during 72 combats involving homo- and heter-ogametic encounters between opponents. Analysis of the data matrix was carried out by the nonmetric multivariate Smallest Space Analysis (SSA-II). The results indicate that (a) aggression patterns, involving agonistic conflict and territorial variables, are higher in heterogametic encounters than in homogametic ones; and (b) aggression is higher between contiguous chromosome forms (2n = 58-60, and 2n = 52-58) than between noncontiguous ones (2n = 52-60). Both a and b suggest that high interspecific aggression appears to be adaptively selected at final stages of speciation in mole rats as a premating isolating mechanism which reinforces species identification and establishes parapatric distributions between the evolving species.
Transcription termination and late control in phage lambda.
Authors: Roberts J W
Published: May 2006

A transcription termination site occurs between the promoter for late gene expression of bacteriophage lambda and the late genes themselves. It is proposed that the lambda Q gene product controls late gene expression by over-coming this termination barrier.
Mechanism of activation of adenylate cyclase by cholera toxin.
Authors: Sahyoun N , Cuatrecasas P
Published: May 2006

Cholera toxin (choleragen) can stimulate adenylate cyclase [EC 4.6.1.1; ATP pyrophosphate-lyase (cyclizing)] activity in whole particulate fractions or purified plasma membranes of homogenates of isolated fat cells provided special precautions are taken to stabilize the enzyme during the required preincubation period. As observed with intact cells, the activation exhibits a protracted (about 25 min) lag phase, and it is blocked by ganglioside GM1 and choleragenoid ("binding" subunit of toxin). The 36,000 molecular weight subunit ("active" subunit), a hydrophobic polypeptide which does not block choleragen binding or action, can directly activate the enzyme in intact cells without a lag phase. Its effects are not blocked by ganglioside GM1 or choleragenoid, yet the stimulated activity exhibits reduced fluoride and enhanced isoproterenol sensitivity, properties characteristic of the choleragen-activated enzyme. Binding of the 125I-labeled 36,000 molecular weight subunit to cells is not saturable and is unaffected by gangliosides, choleragen, or choleragenoid, and the bound material behaves as an integral membrane protein; this protein may simply partition into the membrane matrix. With increasing time of incubation cell-bound choleragen may dissociate into its component subunits, but these remain in the membrane. Using a double antibody immunoprecipitin system, substantial precipitation of cyclase activity occurs with antisera against the 36,000 molecular weight subunit provided toxin activation has occurred. The normal process of activation may involve an initially inactive toxin--ganglioside complex which, as a result of lateral mobility and multivalent binding (lag phase), results in destabilization of the molecule with release of the "active" subunit into the membrane core where it can spontaneously associate with and perturb the cyclase complex.
Anticytokinin activity of substituted pyrrolo[2,3-
d
]pyrimidines
Authors: Skoog Folke , Schmitz Ruth Y. , Hecht Sidney M. , Frye R. Bruce
Published: May 2006

Ten substituted pyrrolo[2,3-
d
]pyrimidines were tested as cytokinins and anticytokinins in the tobacco bioassay. Eight new anticytokinins were identified and two were found to be highly active. The most potent species were 4-cyclohexylamino- and 4-cyclopentylamino-2-methylthiopyrrolo[2,3-
d
]pyrimidine, of which 0.05 and 0.009 μM concentrations, respectively, were required to produce detectable inhibition of the growth of tobacco callus cultured on a medium containing 0.003 μM 6-(3-methyl-2-butenylamino)purine. The inhibition of growth by moderate (≤6.6 μM) concentrations of these compounds was reversible by equal or higher concentrations of 6-(3-methyl-2-butenylamino)purine, but not by indole-3-acetic acid or gibberellic acid. These substituted pyrrolo[2,3-
d
]pyrimidines were also found to enhance bud formation at high cytokinin concentrations, suggesting that a cytokinin may act at more than one cellular site in exerting its growth-promoting and morphogenetic effects.
Carbon monoxide binding to pentacoordinate mercaptide-heme complexes: kinetic study on models for cytochrome P-450.
Authors: Chang C K , Dolphin D
Published: May 2006

Mercaptide anions form exclusively penta-coordinate heme complexes [RS-heme] in polar and nonpolar solution over a wide range of mercaptide concentration. These complexes have a Soret peak at 408 nm and a formation constant of about 2.5 X 10(4) M(-1), and combine with CO to give a CO-cytochrome P-450 type spectrum. Kinetics of CO binding to mercaptide-heme complexes [RS-heme] have been studied by the flash photolysis method. Characteristic constants for this reaction suggest close similarities between [CH3-(CH2)3-S-heme] and cytochrome P-450. The reaction of alkoxide anion with heme has also been examined but no evidence was found for the existence of the [RO-heme-CO[ species.
Conversion of beta-galactosidase to a membrane-bound state by gene fusion.
Authors: Silhavy T J , Casadaban M J , Shuman H A , Beckwith J R
Published: May 2006

We have isolated a series of strains in which the lacZ gene has been fused to one of the maltose operons, such that the synthesis of beta-galactosidase (beta-D-galactoside galactohydrolase; EC 3.2.1.23) is inducible by maltose. The most frequent event that generates such fusions results in strains in which an intact lacZ gene has become a part of the malE,F operon. By using a special selection procedure, we have detected much rarer fusion events resulting in an altered beta-galactosidase molecule. In these strains, we presume that there is a hybrid protein molecule produced, comprised of an NH2-terminal amino acid sequence from a maltose transport protein (malF) and a COOH-terminal amino acid sequence from beta-galactosidase. The hybrid protein, which still retains some beta-galactosidase activity, is found in the cytoplasmic membrane. These results provide information on the component of the malF gene essential for incorporation of its product into the membrane.
Correlation between tumor induction and the large external transformation sensitive protein on the cell surface.
Authors: Chen L B , Gallimore P H , McDougall J K
Published: May 2006

The distribution on the cell surface of the large external LETS protein that is transformation sensitive of normal, transformed and tumorigenic cells was examined by immunofluorescent staining. A correlation was established between the expression of fibril-like LETS protein and the oncogenic capabilities of a series of adenovirus-transformed cell lines. In cells expressing a transformed phenotype in vitro, LETS protein is only detected in cell-cell contact areas, wheras in "untransformed" cells LETS protein is distributed over the cell surface. Transformed cells capable of inducing invasive tumors, and the cells of established tumor lines, have low or undetectable levels of LETS protein, as measured by this method. The results indicate that LETS protein has a role in cell-cell adhesion and that reduced expression of this protein at the cell surface is related to the oncogenic phenotype. This relationship has been established for experimentally induced and spontaneous tumors.
Central regulation of sympathetic neuron development.
Authors: Black I B , Bloom E M , Hamill R W
Published: May 2006

The sixth lumbar (L-6) ganglion has been used to study the central regulation of peripheral sympathetic neuron development. During post-natal ontogeny, tyrosine hydroxylase [tyrosine 3-monooxygenase, L-tyrosine, tetrahydropteridine: oxygen oxidoreductase (3-hydroxylating), EC 1.14.16.2] activity increased 60-fold, while total protein rose 10-fold in the ganglion. Transection of the spinal cord at the fifth thoracic (T-5) segment in neonatal rats prevented the normal developmental increase in tyrosine hydroxylase activity of the L-6 ganglion. However, spinal transection did not alter the ontogeny of tyrosine hydroxylase in the superior cervical ganglion, which derives its innervation from spinal segments rostral to the surgical lesion. Thus, spinal transection interfered with the maturation of sympathetic neurons distal to, but not proximal to, the lesion. The effect of transection on the L-6 ganglion persisted for at least one month, the longest time tested. Our observations suggest that trans-synaptic regulation of adrenergic maturation in the periphery is governed by suprasegmental mechanisms in the central nervous system.
Genetically determined protein polymorphism in the rabbit nervous system.
Authors: Willard M B
Published: May 2006

One of the polypeptides (H1) of the rabbit nervous system occurs in an altered form (H2) in some rabbits. The electrophoretic mobility of H2 on sodium dodecyl sulfate-polyacrylamide gels is about 6% greater than that of H1, suggesting that the two polypeptides differ in molecular weight by about 10,000. The alteration is genetically determined since (i) rabbit phenotypes corresponding to all possible genotypes (H1H1, H1H2, H2H2) were present in an outbred population of rabbits, (ii) the frequency of the phenotype corresponding to the heterozygous genotype (H1H2) was smaller in partially inbred rabbit populations than in outbred populations, and (iii) all of the individuals examined from two partially inbred strains (WH/J and X/J) were of the phenotype that would be expected if they were homozygous (H2H2) for the rare allele of the gene. Preliminary evidence indicates that this polymorphic polypeptide is most abundant in the white matter of the nervous systems of several mammalian species, and is distributed with buffers of low ionic strength and centrifuged at 100,000 Xg.
A mutant of Saccharomyces cerevisiae defective for nuclear fusion.
Authors: Conde J , Fink G R
Published: May 2006

A mutant unable to fuse nuclei during mating has been isolated from standard wild-type Saccharomyces cerevisiae. Tetrad analysis of the mutation responsible for this defect (kar1-1) shows that it segregates as a single Mendelian factor. The defect kn kaf1-1 appears to be nuclear limited. Cytological and genetic evidence shows that in this mutant the events associated with zygote formation are normal until the point of nuclear fusion. The consequence of this defect is the formation of a multinucleate zygote which in subsequent divisions can segregate heterokaryons and haploid heterplasmons.
The caecilian ear: further observations.
Authors: Wever E G , Gans C
Published: May 2006

The structure of the ear is examined in two species of caecilians, Ichthyophis glutinosus and I. orthoplicatus, and the sensitivity to aerial sounds is assessed in terms of the electrical potentials of the cochlea. The results are in general agreement with previous reports on other caecilian species.
Dependence of interferon induction on nucleic acid conformation.
Authors: Bobst A M , Torrence P F , Kouidou S , Witkop B
Published: May 2006

UV and circular dichroism characteristics of duplex analogs belonging to the (A)n-(U)n and (I)n-(C)n series were determined to assign qualitatively the nature of conformational differences caused by 5-pyrimidine and c7 purine substitutions in such duplexes. Evidence is presented which shows that 5-pyrimidine substitution by bromine or methyl changes the duplex conformation of both series in a similar way, if at all. A c7 substitution in the purine ring affects the duplex conformation of the members in the same series similarly, but the conformational change appears to be different for the two series. To wit, it is proposed that in the duplexes the effect of the change (A)n leads to (c7A)n is an increase of the positive base tilt, whereas the change (I)n leads to (c7I)n causes a decrease where (c7A)n is poly (7-deazaadenylic acid) and (c7I)n is poly(7-deazainosinic acid), respectively. Poly(5-bromocytidylic acid) (br5C)n proved to be useful as a sensor strand for the intepretation of the spectroscopic data. The circular dichroism findings correlate well with observations made earlier on the interferon inducing ability for such duplexes, namely, duplexes based on the (c7A)n are inactive as interferon inducers, whereas duplexes based on (c7I)n are potent inducers. Furthermore, a 5-pyrimidine substitution does not substantially affect the interferon inducing ability, unless the thermal stability of the analog becomes critical, as in the case of (A)n-(br5U)n. Thus, this study provides the first evidence to link the interferon-inducing ability of a nucleic acid to a defined physical parameter of double helix, and reinforces the concept that interferon induction is dependent on the recognition of a particular spatial and steric organization of a double-stranded RNA.
Recombination promoted by superhelical DNA and the recA gene of Escherichia coli.
Authors: Holloman W K , Radding C M
Published: May 2006

When a mixture of superhelical DNA (RFI) of phage phiX174 am3 and fragments of single-stranded DNA from wild-type phiX174 was added to spheroplasts of E. coli carrying an amber suppressor, several percent of the progeny phage were recombinant. The yield of wild-type progeny was 10(3) to 10(4) times lower when the fragments came from phiX174 am3 or phage G4 am+, or when fragments were absent. Fewer recombinants were produced in proportion to the decrease in the fraction of RFI in samples treated with S1 nuclease, whereas the total yield of phage did not decrease. Transfection by fragments and superhelical DNA produced 20 to 100 times more recombinants than transfection by fragments and either nicked circular DNA or relaxed closed circular DNA. Transfection of a recA- strain by RFI DNA and fragments yielded 5-10% as many recombinants as transfection of a rec+ strain. This partial requirement for recA was bypassed by transfection with complexes of RFI AM3 DNA and am+ fragments made in vitro.
DNA methylation in adenovirus, adenovirus-transformed cells, and host cells.
Authors: Gunthert U , Schweiger M , Stupp M , Doerfler W
Published: May 2006

DNAs of adenovirus type 2 and type 12 contain low amounts of methylated bases (0.01 and 0.02% N6-methyl-adenine per adenine, if any, and 0.04 and 0.06% 5-methylcytosine per cytosine for type 2 and type 12, respectively), whereas the DNA of the mammalian host cells contains much more 5-methylcytosine (3.57% for human KB cells). The DNA of hamster cells transformed by adenovirus type 12 contains 3.11 and 3.14% 5-methycytosine (HA12/7 and T627 cells, respectively), whereas the DNA from untransformed hamster cells (BHK21 cells) contains 2.22% 5-methylcytosine. In the DNA of human and hamster cells, little, if any, N6-methyladenine was detected. Methylation of DNA was determined by a sensitive method based on two consecutive steps of two-dimensional thin-layer chromatography of the radioactively labeled DNA bases. By this procedure the detection limits of 5-methylcytosine and N6-methyladenine could be lowered to 0.01% per main base.
Acitivity of yeast extracts in cell-free stimulation of DNA replication.
Authors: Jazwinski S M , Edelman G M
Published: May 2006

Extracts of the cytoplasm of disrupted spheroplasts of Saccharomyces cerevisiae (bakers' yeast) stimulated DNA synthesis in a cell-free system consisting of nuclei from spleen cells of the frog Xenopus laevis, The stimulation required Mg++8 ATP, and the deoxynucleoside triphosphates, was saturated by an excess of nuclei or extract, and had kinetics resembling those obtained previously with extracts from mammalian and avian cells. After addition of the yeast extract, replication "eyes" were formed in the DNA from the nucleochromatin of the frog, suggesting that the extract stimulated the initiation of DNA replication. The activity was susceptible to heat, was nondialyzable, and was abrogated by tryptic digestion. Temperature-sensitive mutants of the cell division cycle (cdcmutants 4,7,8, and 28) grown at permissive temperature (23 degrees) yielded extracts that were capable of stimulating DNA replication. When the cells were incubated for one generation at the nonpermissive temperature (36 degrees), their extracts showed very low or no activity. All of these mutants are deficient in events of the dependent pathway leading to initiation of DNA synthesis in the yeast cell cycle. A ts mutant, cdc10, deficient in the separate pathway for cytokinesis, showed little or no loss of activity at the nonpermissive temperature. These data indicate that the "initiation" activity, as assayed in vitro, is subject to control in the yeast cell cycle, and its appearance may be one of the terminal events in the pathway leading to DNA synthesis. The finding that extracts from yeast cells can stimulate DNA synthesis in nucleochromatin from frog cells, and the fact that the cdc mutants 4,7,8, and 28 describe a dependent pathway terminating in development of "initiation" activity, are in accord with the hypothesis that the function of proteins in the dependent pathways of the cell cycle is conserved during evolution.
Quantized generation time in mammalian cells as an expression of the cellular clock.
Authors: Klevecz R R
Published: May 2006

The distribution of possible generation times in mammalian cells does not appear to be continous within the limits of range for each cell type; rather, generation time is quantized in multiples of 3-4 hr. Synchronous cultures of Chinese hamster V79 cells were prepared using manual and automated methods to select and stage mitotic cells. Using synchronous cultures and time-lapse video tape microscopy, it was possible to show that generation times within a population of mitotically selected cells normally disperse in a quantized fashion, with intervals of 3-4 hr occurring between bursts in division. In addition, at temperatures above 37 degrees, V79 cells have a 7.5-8.5 hr modal cell cycle, while at temperatures from 36.5 degrees to 33.5 degrees the modal cell cycle is 11-12 hr long. A survey of the synchrony literature reveals that the tendency to preferred generation times holds between cell lines. The distribution of modal generation times from a variety of different cell types forms a series with a similar interval but with a greater range of values than that observed here for V79 cells. To satisfy the published data and the work presented here, I propose a subcycle, Gq, which has a traverse time equal to the period of the clock. The period appears to be fixed at close to the same value in all mammalian somatic cells. The timekeeping mechanism appears to be temperature compensated, since the time required to traverse Gq is constant at temperatures between 34 degrees and 39 degrees. It is suggested that cell cycle time increases at lower temperatures, lower serum concentration, and high cell densitite because the number of rounds of traverse through Gq increases.
Biphasic stimulation of polyamine biosynthesis in primary mouse kidney cells by infection with polyoma virus:uncoupling from DNA and rRNA synthesis.
Authors: Goldstein D A , Heby O , Marton L J
Published: May 2006

Infection of primary cultures of mouse kidney cells with polyoma virus causes a biphasic increase in the activities of L-ornithine decarboxylase (ODC; L-ornithine carboxy-lyase; EC 4.1.1.17) and S-adenosyl-L-methionine decarboxylase (SAMD; S-adenoxyl-L-methionine carboxy-lyase; EC 4.1.50), as well as in the level of the polyamines putrescine, spermidine, and spermine. An early peak occurs during the period when early viral mRNA is synthesized and prior to the onset of virus-induced synthesis of host cell DNA. A late peak coincides in time with the maximum rate of virus-induced synthesis of cellular DNA. A similar biphasic stimulation of polyamine synthesis is induced even when DNA synthesis is prevented by 5-fluorodeoxyuridine. Actinomycin D (AMD) in a dose that inhibits rRNA synthesis causes no inhibition of ODC or SAMD. In a dose that inhibits mRNA synthesis as well, short-term AMD treatment causes "superinduction" of ODC but inhibition of SAMD. Prolonged treatment with the high dose of AMD inhibits ODC as well, indicating that late ODC activity may be dependent on mRNA synthesized during early infection. Cycloheximide effectively obliterates the ODC and SAMD activities during the entire infectious cycle. Uncoupling from DNA and rRNA synthesis suggests that polyamine synthesis is regulated independently of these events. The experiments with AMD and cycloheximide suggest that the formation of ODC is subject to post-transcriptional control, whereas that of SAMD is regulated primarily at the transcriptional level.
Survival of fetal rat pancreases frozen to -78 and -196 degrees.
Authors: Mazur P , Kemp J A , Miller R H
Published: May 2006

Transplantation of pancreases may have clinical utility in the treatment of diabetes, for it has been shown that chemically induced diabetes in rats can be reversed by the transplantation of greater than or equal to four syngeneic fetal pancreases. Allogeneic transplants produce serious immunological problems, but the problems could be ameliorated if tissue-typed organs could be stored in the frozen state. Unfortunately, nearly all attempts to freeze organs have failed. Nevertheless, recent developments in the physical-chemical analysis of freezing injury and its successful application to the freezing of mammalian embryos encouraged us to attempt the freezing of 16 1/2- to 17 1/2-day intact fetal pancreases. The analysis indicated that to achieve success pancreases would have to be cooled less than 1 degree/min and diluted extremely slowly after thawing. Experiments with embryos and red cells indicated that high survivals might require high concentrations of protective solutes and slow warming. These predictions were accurate. After freezing to -78 or -196 degrees and thawing under optimal conditions, the fetal pancreases synthesized 80-100% as much protein as unfrozen controls and they yielded viable allografts. Optimal conditions included suspension in 2 M dimethylsulfoxide, freezing at 0.3 degrees/min, and slow dilution to preclude osmotic shock.
Identification of prekallikrein and high-molecular-weight kininogen as a complex in human plasma.
Authors: Mandle R J , Colman R W , Kaplan A P
Published: May 2006

Prekallikrein and high-molecular-weight kininogen were found associated in normal human plasma at a molecular weight of 285,000 as assessed by gel filtration on Sephadex G-200. The molecular weight of prekallikrein in plasma that is deficient in high-molecular-weight kininogen was 115,000. This prekallikrein could be isolated at a molecular weight of 285,000 after plasma deficient in high-molecular-weight kininogen was combined with plasma that is congenitally deficient in prekallikrein. Addition of purified 125I-labeled prekallikrein and high-molecular-weight kininogen to the respective deficient plasma yielded a shift in the molecular weight of prekallikrein, and complex formation could be demonstrated by incubating prekallikrein with high-molecular weight kininogen. This study demonstrates that prekallikrein and high-molecular-weight kininogen are physically associated in plasma as a noncovalently linked complex and may therefore be adsorbed together during surface activation of Hageman factor. The complex is disrupted when these proteins are isolated by ion exchange chromatography.
Prediction of three-dimensional structures of enzyme-substrate and enzyme-inhibitor complexes of lysozyme.
Authors: Pincus M R , Zimmerman S S , Scheraga H A
Published: May 2006

Conformational energy calculations were used to predict the three-dimensional structures of enzyme-substrate and enzyme-inhibitor complexes of lysozyme. A global search method, involving the use of a disaccharide fragment molecule, was used initially to determine all favorable binding regions at the active site. It is shown that the binding of a series of (nonfragmented) oligomers of N-acetylglucosamine is highly specific. The results show further that (a) the enzyme recognizes only one backbone conformation of the oligomer, corresponding to a left-handed helix, and (b) for saccharides containing two or more N-acetylglucosamine residues, two residues bind preferentially to the C and D sites. The calculations also suggest that the chair form of N-acetylglucosamine can bind to the D region. The saccharide residues of tetra-N-acetylglucosamine bind to the A-B-C-D sites, with the residues at the A-B-C sites having essentially the same conformation and orientation as those in the x-ray structure of tetra-N-acetylglucosamine-delta-lactone bound to lysozyme.
Regulation of protein synthesis in rabbit reticulocyte lysates: purification and initial characterization of the cyclic 3':5'-AMP independent protein kinase of the heme-regulated translational inhibitor.
Authors: Ranu R S , London I M
Published: May 2006

The heme-regulated translational inhibitor (HRI) has been purified 4800-fold. On electrophoresis in sodium dodecyl sulfate/polyacrylamide gel, the purified HRI showed one major polypeptide band. The purified HRI inhibits protein synthesis in lysates containing optimal levels of hemin with inhibition kinetics which parallel those observed in heme-deficiency. Data are presented which are consistent with an enzymatic function of HRI in the inhibition of protein synthesis. The HRI is an adenosine 3':5'-cyclic monophosphate independent protein kinase which phosphorylates the small subunit (38,000) but not the large subunits (52,000 and 50,000) of the initiation factor which forms a ternary complex with Met-tRNAf and GTP. This evidence supports the hypothesis that inhibition of protein synthesis by HRI involves the phosphorylation of the initiation factor. These findings are discussed in relation to various models for the regulation of protein kinase activity by heme. (see article).
Subnuclear systems for synthesis of simian virus 40 DNA in vitro.
Authors: Edenberg H J , Waqar M A , Huberman J A
Published: May 2006

We have developed two subnuclear systems for synthesis of DNA of simian virus 40 in vitro. We prepare chromatin from infected cells by the method of Hancock [(1974) J. Mol. Biol. 86, 649-663]; these "chromatin bodies" can be disrupted and large debris can be pelleted, leaving a supernatant ("soluble system"). Both chromatin bodies and the soluble system incorporate deoxyribonucleoside triphosphates into nucleoprotein complexes that contain simian virus 40 DNA. The DNA labeled in short pulses sediments in neutral sucrose gradients slightly faster than mature simian virus 40 DNA, as expected for replicating intermediate. When rebanded in alkaline sucrose gradients, about half of the radioactivity is found in short strands (200-300 nucleotides) and half in longer strands (up to full viral size). When these systems are supplemented with a cytoplasmic preparation from HeLa cells, synthesis is stimulated about 5-fold, and the short strands are converted into strands of up to full viral length as well as into covalently closed circles. These subnuclear DNA-replicating systems should be useful for biochemical fractionation and characterization of some of the proteins required for DNA replication.
Brain tubulin polymerization in the absence of "microtubule-associated proteins".
Authors: Himes R H , Burton P R , Kersey R N , Pierson G B
Published: May 2006

Pure tubulin dimer, purified by phosphecellulose chromatography to remove microtubule associated proteins, can be assembled into microtubules in the presence of dimethyl sulfoxide. The surfaces of such microtubules are devoid of filamentous material. The reaction is rapid and strongly dependent on protein concentration. No microtubule formation occurs from the purified tubulin when dimethyl sulfoxide is omitted.
Histones H3 and H4 interact with the ends of nucleosome DNA.
Authors: Simpson R T
Published: May 2006

Isolated HeLa cell nucleosomes (core particles) were labeled at the 5'-termini of their DNA with 32P using [gamma-32P]ATP and polynucleotide kne by sequential methylation, depurination, Schiff base formation, and reduction with sodium borhydride. After digestion of the noncrosslinked DNA by DNase I and venom phosphodiesterase, histones were separated by gel electrophoresis and those crosslinked to the 5'-termini were identified by 32P-autoradiography. Histones H3 and H4 occur with equeal frequency as the nearest protein neighbors to the end of the DNA in nucleosomes. Histone arrangements within the core particle compatible with these results are discussed.
Some correlations between specificity and sequence of the first complementarity-determining segments of human kappa light chains.
Authors: Kabat E A , Wu T T , Bilofsky H
Published: May 2006

Examination of the sequences of the first complementarity-determining segments of the light chains of two IgM cold agglutinins agains blood group I, four monoclonal IgM antibodies against IgG proteins, and of three Bence Jones proteins provides clues for predicting which residues contribute to antibody specificity and indicates that these predictions may be tested by evaluating recovery of antibody activity and specificity when various light chains are recombined with homologous and heterologous heavy chains.
Modification of adenylate cyclase activity in LM cells by manipulation of the membrane phospholipid composition in vivo.
Authors: Engelhard V H , Esko J D , Storm D R , Glaser M
Published: May 2006

Adenylate cyclase [atp pyrophosphate-lyase (cyclizing): EC 4.6.4.4] activities were examined in mouse LM cell (fibroblast) membranes that were supplemented with ethanolamine and/or fatty acids. The supplements were incorporated into the plasma membrane phospholipids in significant amounts. Fatty acid supplementations had distinct effects as compared to polar head group supplementations. All lipid supplementations increased basal adenylate cyclase activity relative to control cells grown in choline-containing medium. Double supplementation with ethanolamine and linoleate increased the specific activity of adenylate cyclase up to 4-fold. Activity in the presence of fluoride was unaffected by ethanolamine supplementation, but was increased by fatty acid supplementation. In contrast, prostaglandin E1 stimulation was 4.2-fold in controls and ethanolamine and/or elaidate supplements, 6-fold in choline plus linoleate supplements, and 3.1-fold in ethanolamine plus linoleate supplements. Differences in activity could not be ascribed to changes in membrane protein composition in supplemented cells, and could be abolished by detergent solublization. Fluidity of the supplemented membranes was monitored by fluorescence polarization, and no correlation was observed between membrane viscosity and adenylate cyclase activity or hormone stimulation. These results emphasize the importance of the membrane lipid phase for this enzyme.
Induction of mouse type-C virus by translational inhibitors: evidence for transcriptional derepression of a specific class of endogenous virus.
Authors: Cabradilla C D , Robbins K C , Aaronson S A
Published: May 2006

Several biologically distinguishable type-C RNA viruses are genetically transmitted in mouse cells. In the present report, chemicals that inhibit several different steps in protein synthesis are shown to cause marked increases in the cellular concentration of virus-specific RNA and the subsequent induction of virus. Analysis of the effect of translational inhibitors on mouse embryo cells of different genotypes indicates that activation of viral RNA is specific for one endogenous virus class and is a dominant genetic characteristic. Two lines of evidence favor the hypothesis that the induction of viral RNA involves transcriptional derepression rather than an alteration in its post-transcriptional processing. First, nuclear and cytoplasmic fractions of induced cells are shown to demonstrate similar increases in their concentrations of virus-specific RNA. Second, the decay of induced viral RNA following inhibition of further RNA synthesis by actinomycin D is not prevented by continued exposure to the inducer. These findings weigh heavily against the possibility that translational inhibitors act to stabilize viral RNA post-transcriptionally. The results are consistent with a model in which the expression of one class of endogenous virus is regulated by a labile repressor protein acting at a transcriptional level.
Antiviral effect on MS-2 coliphage obtained with a synthetic antigen.
Authors: Langbeheim H , Arnon R , Sela M
Published: May 2006

The coat protein of bacteriophage MS-2 was cleaved with cyanogen bromide to yield three fragments, possessing the sequence 1-88 (P1), 89-108 (P2), and 109-129 (P3), respectively. The mixture of peptides P2 and P3, which could not be separated, was found capable of inhibiting the neutralization of the phage by antiserum to the whole MS-2. The peptides corresponding to P2 and P3 were therefore synthesized. The synthetic P3 had no capacity to interfere with neutralization of MS-2, not did its macromolecular conjugate with multichain poly(DL-alanine) elicit neutralizing antibodies. On the other hand, the synthetic P2 was very efficient in inhibiting the inactivation of the phage by the antiserum against phage. Furthermore, a synthetic antigen prepared by attachment of P2 to multichain poly(alanine) incuded antiserum in rabbits that was capable of neutralizing MS-2 activity almost as efficiently as the antiserum prepared against the intact coat protein. This inactivation is specific, because it can, in turn, be totally inhibited by P2 peptide.
Immunological crossreaction between alpha-fetoprotein and albumin.
Authors: Ruoslahti E , Engvall E
Published: May 2006

Alpha-fetoprotein (AFP), a fetal protein associated with certain tumors, and serum albumin did not corssreact immunologically in native form. Unfolding of their polypeptide chains by reduction of the disulfide bonds followed by carboxamidomethylation produced derivatives with immunochemical properties different from those of the native proteins. Precipitating reactions and radioimmunoassays preformed with antibodies to such unfolded derivatives showed strong crossreactions between albumin and AFP. These assays were found to lack species specificity: AFPs and albumins from different species were equally active. Several other proteins unrelated to AFP or albumin did not react or reacted much less in these assays. These results support the conclusions derived from recent sequence data that AFP and albumin are structurally related and have a common ancestral gene.
Biological and serological characterization of radiation leukemia virus.
Authors: Declève A , Lieberman M , Ihle J N , Kaplan H S
Published: May 2006

Radiation leukemia virus, isolated from radiation-induced lymphomas in C57BL/Ka mice and propagated in that strain, is thymotropic and leukemogenic in vivo but replicates poorly, if at all, in mouse and mink fibroblast cultures in vitro. Comparative studies indicate that this naturally occurring virus is distinct from the previously recognized classes of endogenous murine ecotropic and xenotropic C-type viruses which are capable of replication on fibroblasts (fibrotropic) but are neither thymotropic nor leukemogenic. These studies also demonstrate that a differentiation-specific restriction system governing the replication of the murine ecotropic C-type viruses operates in addition to the previously defined Fv-1 and SRV gene restriction systems.
Magnetic resonance studies of concanavalin A: location of the binding site of alpha-methyl-D-mannopyranoside.
Authors: Fuhr B J , Barber B H , Carver J P
Published: May 2006

The longitudinal nuclear magnetic relaxation times of the methyl protons of alpha-methyl-D-mannopyranoside have been measured at 90 MHz and 270 MHz in solutions of concanavalin A complexed with: (i) Mn2+ and Ca2+; and (ii) Zn2+ and Ca2+. Zn2+ and Mn2+ are known to bind in site S1 and Ca2+ in site S2 of concanavalin A. Both sites must be occupied before monosaccharides will bind to the protein. In order to extract T1p, the paramagnetic contribution to the bound methyl relaxation time, from these observations the relaxation time of uncomplexed sugar was determined. Free Mn2+ contributed insignificantly to the latter value; however, outer sphere relaxation was found to be large at bound Mn2+ concentrations greater than 1 mM. Comparison of the results obtained at the two frequencies allowed the determination of the correlation time for the interaction between the methyl protons and the bound Mn2+ and the distance between them (21.5 +/- 1.2 A). In contrast to previous results from nuclear magnetic resonance studies, this distance is consistent with binding at the cavity proposed for the saccharide binding site by Becker et al. [J. Biol. Chem. 250, 1513 (1975)], although it does not preclude possible binding sites on the surface of the molecule.
Free energy levels and entropy production in muscle contraction and in related solution systems.
Authors: Hill T L , Simmons R M
Published: May 2006

"Basic" and "gross" free energy levels of a macromolecule such as myosin or Na,K-ATPase, defined in a previous publication, are discussed here for two relatively complicated cases: a six-state kinetic diagram of the sort that could be used to describe the actin activation of myosin-ATPase in solution; and muscle contraction, where a similar kinetic diagram is needed for each value of a positional variable X.
Copper-induced activation of aortic lysyl oxidase in vivo.
Authors: Harris E D
Published: May 2006

Raising day-old chicks on diets lacking copper severely depressed the activity of lysyl oxidase, a copper metalloenzyme in connective tissue. Administration of CuSO4 either through the diet or through intraperitoneal injections restored the lysyl oxidase activity in aortic tissue. Two hours after the chicks received CuSO4 (1 mg/kg) the activity of lysyl oxidase rose rapidly to attain, within 4-6 hr, a new steady-state level which was five to 20 times higher than the basal (saline-injected) activity. Twenty hours after copper administration, activity was still higher, in some experiments double that achieved at 6 hr. Very low amounts of cycloheximide injected intraperitoneally 45 min before and 3 hr after copper suppressed the activation response by two-thirds. Cycloheximide given 2 or 4 hr after the copper was only one-half as effective. Actinomycin D caused only a 10-15% inhibition of the copper-induced activation. The data suggest that copper is a key regulator of lysyl oxidase activity in aorta and may in fact be a major determinant of the steady-state levels of the enzyme in that tissue.