bluuebunny/crossref_metadata_2025 huggingface dataset:
Enhanced antibody affinity in sublethally irradiated mice and bone marrow chimeras.
Authors: Doria G , Gorini G , Di Michele A
Published: May 2006

Sublethally irradiated mice primed with dinitrophenyl (Dnp)-keyhole limpet hemocyanin immediately after irradiation or 30 days later and subsequently boosted with a second injection of antigen displayed a secondary response to Dnp characterized by antibody affinity greater than that in unirradiated controls. Also, in radiation chimeras primed with Dnp-keyhole limpet hemocyanin 120 days after syngeneic or allogeneic bone marrow transplantation the antibodies against Dnp produced after boosting were of higher affinity than the antibodies raised in normal mice. These findings are tentatively attributed to lack of suppressor thymus-derived lymphocytes (T cells) in sublethally irradiated mice and bone marrow chimeras, in which the enhanced ability to produce antibodies of high affinity may compensate for quantitative defects of the immune system.
Genetic control of renin activity in the submaxillary gland of the mouse.
Authors: Wilson C M , Erdös E G , Dunn J F , Wilson J D
Published: May 2006

Administration of androgen to female mice is known to increase the level of several proteins in the submaxillary gland, including nerve growth factor, epidermal growth factor, esteroproteolytic activity, and renin. In the present study, renin activity has been assessed in extracts of submaxillary gland of female mice from two inbred strains (SWR/J and C57BL/10J), from F1 and F2 hybrids, and from backcrosses between F1 and parental strains. In both uninduced and induced mice, renin activity of submaxillary gland was more than 100-fold greater in SWR/J than in C57BL/10J mice as measured by either an enzymatic assay or an immunodiffusion method. This difference was not due to differences in plasma testosterone levels between the strains, and the enzymes from the two strains had similar pH optima, substrate specificities, heat stabilities, and apparent Michaelis constants. In the submaxillary gland the difference was relatively specific for renin because increases in esteroproteolytic activity, nerve growth factor, and epidermal growth factor after androgen treatment appeared to be similar in both strains. Studies with the various hybrids indicate that the difference in renin activity between the two strains is apparently due to a single regulatory gene.
Thymic activity in severe combined immunodeficiency diseases.
Authors: Incefy G S , Dardenne M , Pahwa S , Grimes E , Pahwa R N , Smithwick E , O'Reilly R , Good R A
Published: May 2006

Thymic function was evaluated by quantitation of circulating thymic factor in patients with several forms of severe infantile immunodeficiency diseases. Direct quantitation of thymic factor in serum of patients with severe combined immunodeficiency revealed heterogeneity of this syndrome by this parameter, as was also shown by study of susceptibility of the marrow cells to differentiation in vitro. Thymic factor was not detectable in one patient with severe combined immunodeficiency, but was present in normal or near-normal concentrations in three others. Circulating levels of this hormonal activity were also not detectable in a patient with DiGeorge athymic syndrome. Following marrow or fetal liver transplantation, which corrected the severe combined immunodeficiency thymic factor levels either increased slightly or did not change appreciably. Fetal thymic transplantation, which together with fetal liver transplantation corrected the immunodeficiency in one patient with severe combined immunodeficiency, was associated with increase of thymic factor to normal levels. Fetal thymus transplantation alone, which was employed to correct the immunodeficiency of DiGeorge athymic syndrome, caused an increase in thymic factor activity to normal or near normal levels in this patient.
Characterization of a delta-electroencephalogram (-sleep)-inducing peptide.
Authors: Schoenenberger G A , Monnier M
Published: May 2006

A peptide that induces slow-wave (delta) and spindles electroencephalogram enhancement after intraventricular (brain) infusion has been isolated from rabbits and given the name delta-sleep-inducing peptide (DSIP). Amino acid seqeunce: Trp-Ala-Gly-Gly-Asp-Ala-Ser-Gly-Glu. This compound, five possible metabolic products (containing residues 1--8, 2--9, 2--8, 1--4, and 5--9), two nonapeptide analogues with two amino acids exchanged, and a related tripeptide (Trp-Ser-Glu) were synthesized. All nine synthetic peptides were infused intraventricularly in rabbits under double-blind conditions. A total of 58 rabbits including controls were evaluated. The electroencephalogram leads from the neocortex and the archicortex were directly fast-Fourier transformed and analyzed by a Univac 1108 computer system. Only the delta-sleep-inducing peptide (snythetic) showed significant and specific enhancement/induction of delta and spindle electroencephalogram patterns.
Heavy water as a tool for study of the forces that control length of period of the 24-hour clock of the hamster.
Authors: Richter C P
Published: May 2006

In alternating 12-hr periods of light and darkness, start of the dark period entrains the hamster's 24-hr clock. Blinding or constant darkness frees the clock of entrainment by allowing it to run faster or slower than 24 hr. Constant light frees the clock from entrainment and permits it to run slower than 24 hr--that is, lengthening its period. Heavy water given in drinking water linearly lengthens the period of the 24-hr clock of blinded hamsters or of hamsters kept in constant darkness in direct proportion to concentration of heavy water (1--50%). Heavy water (1-35%) has very different effects on length of the periods of the 24-hr clock when given under conditions of alternating 12-hr periods of light and darkness. Under these conditions, length of the period is controlled by three factors: (i) heavy water which slows the 24-hr clock; (ii) constant light which also slows the 24-hr clock; (iii) the counteracting effects of entrainment. It is thus possible to observe the effects of all three forces simultaneously in the same animal. The clock slowed by heavy water (1--20%) showed a strong tendency to return to a 24-hr entrainment whenever possible. On a 50% concentration of heavy water, the length of period of the clock became markedly lengthened but very constant and apparently independent of all external and internal disturbances.
31P nuclear magnetic resonance studies of glycogen phosphorylase from rabbit skeletal muscle: ionization states of pyridoxal 5'-phosphate.
Authors: Feldmann K , Hull W E
Published: May 2006

31P nuclear magnetic resonance (NMR) at 72.8 MHZ has been used to study glycogen phosphorylase from rabbit muscle (1,4-alpha-D-glucan:orthophosphate alpha-glucosyltransferase, EC 2.4.1.1) at concentrations as low as 25 mg/ml, using a WH-180 wide-bore superconducting spectrometer. The use of a thio analogue for 5'-AMP and arsenate for inorganic phosphate allowed the observation of three distinct forms of enzyme-bound pyridoxal 5'-phosphate at --0.2 ppm (Form I), --2 to --3 ppm (Form II), and --3.5 ppm (Form III) relative to triethylphosphate. Conversion of I to III occurs by activation of phosphorylase either by formation of a ternary complex of phosphorylase b with effector and arsenate or, more efficiently, by direct phosphorylation to give the a form of the enzyme. The ionization state and exposure to solvent of each of the three forms is inferred from the 31P NMR data.
Molecular weight and valence of the cell-surface receptor for immunoglobulin E.
Authors: Newman S A , Rossi G , Metzger H
Published: May 2006

The molecular weight of the active solubilized cell-surface receptor for immunoglobulin E (IgE) was measured in nonionic detergent. The diffusion coefficient was estimated by gel filtration, the partial specific volume was estimated from the differential sedimentation in sucrose gradients prepared from H2O and D2O, and the sedimentation constant was estimated from the same centrifugation experiments. The receptor has an apparent molecular weight of 130,000. Its high partial specific volume (0.81 cm3/g) suggests that bound detergent contributes significantly to the mass. The molecular weights of the receptor-IgE complex and of unbound IgE determined similarly were 310,000 and 200,000 respectively, clearly showing that the receptor is univalent. The implications of these results for the subunit structure of the receptor, receptor-membrane integration, and a possible mechanism of receptor triggering are discussed.
Granulocyte collagenase: selective digestion of type I relative to type III collagen.
Authors: Horwitz A L , Hance A J , Crystal R G
Published: May 2006

Collagenases produced by human polymorphonuclear leukocytes, human lung fibroblasts, and rabbit pulmonary alveolar macrophages were compared in their ability to digest soluble native type I and type III collagens. While the fibroblast and macrophage collagenases attacked the two substrates at approximately equal rates, the leukocyte collagenase attacked type I collagen preferentially (15:1) in comparison to type III collagen. This was true with human or rabbit collagen substrates. Thus, proteolysis of collagen, particularly in acute inflammation, may have a significant role in controlling the types of collagen present in connective tissue.
Triple-helix formation on ribosome-bound nascent chains of procollagen: deuterium-hydrogen exchange studies.
Authors: Veis A , Brownell A G
Published: May 2006

Polyribosomes containing nascent [3H]proline-labeled collagen chains were isolated from chick embryo fibroblasts in culture. These nascent chains were nearly completely hydroxylated, as indicated by the presence of [3H]hydroxyproline and high hydroxyproline/proline ratios. The polyribosomes were suspended in D2O at 15 degrees and the infrared spectrum was determined using a reference cell containing collagen-depleted polyribosomes in D2O, matched to equal RNA content. The amide I and amide II bands were observed. When the polyribosomes were heated in D2O at 44 degrees in the infrared cells, the N--D amide II absorbance at 1480 cm-1 increased markedly, indicating that H leads to D exchange had occurred. Collagen-depleted polyribosomes showed no such changes in absorbance at 1450-1480 cm-1 upon heating. Polyribosomes recovered from the infrared cells after treatment at 44 degrees and cooling still contained collagen, as indicated by their [3H]hydroxyproline content. These data indicate that nascent collagen bound to the polyribosomes can assume a hydrogen-bonded structure. Taken with prior data showing that the nascent collagen was also resistant to pepsin digestion, it is suggested that the collagen examined is in triple-helix conformation. Because the nascent polyribosome-bound collagen is nearly fully hydroxylated, it must be considered that triple-helix formation can occur between nascent chains while they are attached to the endoplasmic reticulum surface and that chain association and triple-helix formation in vivo may well occur before rather than after release.
Assembly of biologically active proheads of bacteriophage lambda in vitro.
Authors: Murialdo H , Becker A
Published: May 2006

Bacteriophage lambda DNA can be packaged in vitro into preformed proheads to generate plaque-forming units. This complex set of reactions is initiated when lambda DNA is mixed with the product of the phage A gene, and proheads. Because proheads are an essential early reactant, the system has potential as an assay for the formation of biologically active proheads. When extracts of cells infected with certain lambda head mutants (for example, B--, C--, Nu3--, and E--) are used as the prohead donor, plaque-forming units are not produced. However, when extracts of E- - and Nu3- - infected cells are first reacted together the combination provides prohead-donor activity to the in vitro packaging system. In vitro assembled, biologically active proheads have the same sedimentation properties and electron micrsocopic appearance as "wild-type" proheads isolated from lambdaA-D- -infected cells. Centrifugation analysis shows that the Nu3- extract contributes gpE, the major capsid protein, to the reaction in the form of monomers or small polymers.
Recognition of two intracellular cobalamin binding proteins and their identification as methylmalonyl-CoA mutase and methionine synthetase.
Authors: Kolhouse J F , Allen R H
Published: May 2006

The granulocyte R-type cobalamin binding protein delivers cobalamin (Cbl) exclusively to hepatocytes, and transcobalamin II delivers Cbl to various mammalian cells. Both protein-Cbl complexes enter cells by pinocytosis, and the protein moieties are rapidly degraded in lysosomes. The liberated Cbl is subsequently bound to a high-molecular-weight intracellular cobalamin binding protein (ICB). The nature of ICB-Cbl is unknown but appears important because ICB-[57Co]Cbl is missing from cultured fibroblasts of a group of patients whose cells take up CN-[57Co]Cbl normally but do not convert it to either of its coenzyme forms. We have examined supernatants of sonicated rabbit livers and have found that 65% of the total endogenous Cbl elutes from Sephadex G-150 as ICB-Cbl and that this fraction also contains the two mammalian Cbl-dependent enzymes, methylmalonyl-CoA mutase (methylmalonyl-CoA CoA-carbonylmutase;EC 5.4.99.2) and methionine synthetase (tetrahydropteroylglutamate methyltransferase; 5-methyltetrahydropteroyl-L-glutamate:L-homocysteine-S-methyltransferase; EC 2.1.1.13). Gradient elution from DEAE-Sephadex reveals that 90--95% of the ICB--Cbl elutes with methylmalonyl-CoA mutase and 5--10% elutes with methionine synthetase. ICB--[57Co]Cbl first appears 2 hr after the intravenous injection of CN[57Co]Cbl bound to granulocyte R-type protein. This ICB-[57Co]Cbl is associated with either methylmalonyl-CoA mutase or methionine synthetase although the latter appears to be formed at a relatively faster rate. Our studies indicate that mammalian cells contain two ICBs, that these proteins are methylmalonyl-CoA mutase and methionine synthetase, and that the primary abnormality in the group of patients mentioned above lies at a step that is common to the formation of both Cbl coenzymes and that precedes the stable binding of Cbl to both methylmalonyl-CoA mutase and methionine synthetase.
Rous sarcoma virus genome is terminally redundant: the 5' sequence.
Authors: Haseltine W A , Maxam A M , Gilbert W
Published: May 2006

When Rous sarcoma virus RNA is transcribed into DNA by the reverse transcriptase, a tRNA primer is elongated into DNA. The primer is near the 5' end of the virus genome; the first major DNA made is a "run-off" product extending 101 bases from the primer to the 5' end of the template. We have studied this DNA molecule to determine the sequence of the first 101 bases at the 5' end of the Rous sarcoma virus genome (Prague strain, subgroup C). Twenty-one bases at the extreme 5' end are also at the 3' end of the virus genome (see D. E. Schwartz, P. C. Zamecnik, and H. L. Weith, this issue, pp. 994-998), and thus this virus is terminally redundant. The existence of this sequence repetition immediately suggests mechanisms by which the growing DNA copy can jump from the 5' end to a 3' end of the template and become circular. The sequence also displays a possible ribosome binding site and enough secondary structure to permit a possible 5'-5' linkage of viral RNA molecules.
Model of protein folding: incorporation of a one-dimensional short-range (Ising) model into a three-dimensional model.
Authors: Tanaka S , Scheraga H A
Published: May 2006

In this paper, we have incorporated a one-dimensional short-range model into a three-dimensional model for protein folding. It has been applied, by extending the concept of the three-step mechanism for protein folding proposed in our previous paper, to simulate the folding of bovine pancreatic trypsin inhibitor, using a Monte Carlo procedure in all three steps, A, B, and C. The statistical mechanical ensemble treatment of the short-range model serves as a constraint on the Monte Carlo procedure, in which conformational transitions are introduced. The preliminary results of 10 independent Monte Carlo trials indicate that, while folding is achieved, improvements are required in order to account for the correct three-dimensional structure of a globular protein.
On the process of cellular division in Escherichia coli: a mutant of E. coli lacking a murein-lipoprotein.
Authors: Hirota Y , Suzuki H , Nishimura Y , Yasuda S
Published: May 2006

A mutant of E. coli lacking a specific outer membrane lipoprotein was found. Both the free and the bound form have been lost in this mutant. No material that cross-reacted with antiserum against lipoprotein was detected by the Ouchterlony test. The mutant was defective in producing mRNA active for lipoprotein synthesis. The mutation leading to the loss of lipoprotein synthesis, referred to as lpo, seems to have arisen during production of an F'. The map position of lpo was at 36.5 min on the E. coli K12 map, in the order man, uidA, lpo, aroD, pps. The lpo mutant grew and divided normally and remained susceptible to bacteriophages lambda, phi80, P1, P2, the T series, and f1, f2, and MS2 in its male derivatives. The mutant was hypersensitive to EDTA and cationic dves and somewhat sensitive to detergents. There was considerable leakage of periplasmic enzymes but passive transport of beta-galactoside was unchanged. These physiological characteristics of the mutant suggest that lipoprotein is involved in maintaining the integrity of the outer envelope structure, by bridging the outer membrane and murein, but not in the vital processes of growth and division.
The cost of evolution and the imprecision of adaptation.
Authors: Darlington P J
Published: May 2006

Comparisons of six hypothetical cases suggest that Haldane overstimated the cost of natural selection by allele substitution. The cost is reduced if recessive alleles are advantageous, if substitutions are large and few, if selection is strong and substitutions are rapid, if substitutions are serial, and if substitutions in small demes are followed by deme-group substitutions. But costs are still so heavy that the adaptations of complex organisms in complex and changing environments are never completed. The rule probably is that most species most of the time are not fully adapted to their environments, but are just a little better than their competitors for the time being.
An Escherichia coli mutant with a temperature-sensitive function affecting bacteriophage Qbeta RNA replication.
Authors: Mandal N C , Silverman P M
Published: May 2006

We report the isolation of E. coli mutant capable of supporting replication of bacteriophage Qbeta at 33 degrees, but not at 40 degrees. Coliphages f2, R23, fd, and yamma formed plaques on mutant cells at both temperatures. Temperature-shift experiments showed that bacteriophage Q beta replication was blocked in the mutant within the first 20-30 min of infection. The defect did not prevent translation of the Qbeta polymerase gene or assembly of catalytically active Qbeta replicase molecules. In fact, mutant cells infected at 40 degrees hyperinduced replicase active both in vivo and in vitro. However, zone sedimentation of the in vivo RNA product showed it to consist of partially double-stranded material sedimenting at 9 S, with little or no viral 32S RNA. The 9S RNA was also found, along with a predominant peak of 32S RNA in parental cells infected at 40 degrees, but not in cells infected at 33 degrees. It thus appears that the temperature-sensitive component is required for viral RNA replication, but not for other RNA synthesis catalyzed by the replicase. Uninfected mutant cells grew normally at 40 degrees in nutrient broth, but not in glucose- or glycerol-minimal media. Revertants selected for their abillity to grow in minimal medium at 40 degrees also supported bacteriophage Qbeta replication at 40 degrees.
Genetic evidence for inducibility of recombination competence in yeast.
Authors: Fabre F , Roman H
Published: May 2006

Recombination between unirradiated chromosomes was induced by UV or x-ray irradiation of haploids followed by a mating with heteroallelic diploids of Saccharomyces cerevisiae. The selected event of intragenic recombination did not involve the participation of the irradiated chromosome and apparently was not caused by lesions introduced into the unirradiated chromosomes by some indirect process. The results favor the idea that recombination is repressed in the majority of vegetative cells and that one effect of radiation is the release of some factor(s) necessary for recombination. Consequently, the proportion of competent cells (i.e., cells able to recombine) in the population increases. This competent state seems necessary not only for the recombinational repair of radiation-induced lesions but also, since recombinants are produced in the absence of such lesions, for spontaneous recombination. Photoreactivation of the UV-irradiated haploids led to a decrease in the production of recombinants. Hence, lesions in the DNA appear to be responsible for the induction of the recombinational ability.
Site of water vapor absorption in the desert cockroach, Arenivaga investigata.
Authors: O'Donnell M J
Published: May 2006

The desert cockroach, Arenivaga investigata, can gain weight by absorption of water-vapor from unsaturated atmospheres above 82.5% relative humidity. Blocking the anus or the dorsal surface with wax does not prevent water vapor uptake, but interference with movements of the mouthparts or blocking the mouth with wax-prevents such uptake. Weight gains are associated with the protrusion from the mouth of two bladder-like extensions of the hypopharynx. During absorption these structures are warmer than the surrounding mouthparts, their surface temperature increasing with relative humidity. This suggests that the surfaces of the bladder-like structures function at least as sites for condensation of water vapor, but the precise location of its transfer into the hemolymph has not yet been identified.
Enzymatic initiation of DNA synthesis by yeast DNA polymerases.
Authors: Plevani P , Chang L M
Published: May 2006

Partially purified yeast RNA polymerases (RNA nucleotidyltransferases) initiate DNA synthesis by yeast DNA polymerase (DNA nucleotidyltransferase) I and to a lesser extent yeast DNA polymerase II in the replication of single-stranded DNA. The enzymatic initiation of DNA synthesis on phage fd DNA template occurs with dNTPs alone and is further stimulated by the presence of rNTPs in DNA polymerase I reactions. The presence of rNTPs has no effect on the RNA polymerase initiation of the DNA polymerase II reaction. RNA polymerases I and III are more efficient in initiation of DNA synthesis than RNA polymerase II. Analyses of the products of fd DNA replication show noncovalent linkage between the newly synthesized DNA and the template DNA, and covalent linkage between the newly synthesized RNA and DNA.
Disagreement between calorimetric and van't Hoff enthalpies of assembly of protein supramolecular structures.
Authors: Sutherland J W
Published: May 2006

The effect of temperature on the extent of association of self-assembling protein polymers is expressed mathematically in terms of the van't Hoff enthalpy of polymerization, deltaHV.H. This quantity has been experimentally defined in two ways--from the respective temperature derivatives of the critical polymerization concentration and of the fractional conversion of protein into polymer. These two definitions are shown not to be identical, except in certain limits. In terms of both definitions, it is shown that deltaHV.H. depends not only upon the enthalpy changes but also upon the corresponding equilibrium constants for the various equilibria involved in polymer formation. This has two consequences: (i) large deltaHV.H. values may result from reactions having small calorimetric enthalpy changes; and (ii) deltaHV.H. can depend strongly on temperature. These considerations are applied to two systems for which there exist considerable experimental data--namely, hemoglobin S and tubulin. The large discrepancy between the calorimetric and van't Hoff enthalpies for the polymerization of tubulin is shown to be explicable in terms of these considerations.
Localization of RNA polymerase in polytene chromosomes of Drosophila melanogaster.
Authors: Jamrich M , Greenleaf A L , Bautz E K
Published: May 2006

RNA polymerase (RNA nucleotidyltransferase) B (or II) and histone H1 of Drosophila melanogster were localized on salivary gland polytene chromosomes using the indirect immunofluorescence technique. RNA polymerase B is present almost exclusively in puffs and interband regions, whereas histone H1 is found primarily in bands. The puff at region 3C, known to be transcriptionally active in larval salivary glands, gives a bright fluorescence with antibodies against RNA polymerase B. This fluorescence disappears after exposure of the larvae to 37 degrees for 45 min. The heat shock treatment results in a general reduction of fluorescence intensity with the appearance of brightly staining heat shock puffs. Heat-induced removal of RNA polymerase molecules from a puff does not immediately alter its morphology. We propose than an interband represents that fraction of the total number of gene copies in a band that are active, the inactive copies being present in a condensed form in the adjacent band. Large puffs would originate through the decondensation and activation of most or all gene copies in a band.
Inactivation and proteolytic cleavage of phage lambda repressor in vitro in an ATP-dependent reaction.
Authors: Roberts J W , Roberts C W , Mount D W
Published: May 2006

We have reproduced in vitro the inactivation of bacteriophage lambda repressor that occurs in vivo when a lambda lysogen is treated with agents such as ultraviolet radiation that attack DNA. ATP and a divalent cation are required for the inactivation reaction. The ind- repressor is insensitive to the inactivation mechanism. A proteolytic cleavage of repressor accompanies inactivation in vitro, as it does in vivo.
Hormone-inducible casein messenger RNA in a serum-free organ culture of whole mammary gland
Authors: Terry P. M. , Banerjee M. R. , Lui R. M.
Published: May 2006

The whole second thoracic mammary gland of estradiol-17β + progesterone primed 3- to 4-week-old BALB/c female mice was induced to pregnancy-like lobulo-alveolar morphogenesis after 6-day cultivation in a serum-free culture medium containing a “growth promoting” hormone mixture, insulin + prolactin + growth hormone (somatotropin) + estradiol + progesterone. No radioimmunologically detectable casein was present in these glands. Subsequent cultivation for another 6 days in a “lactogenic” medium with the hormones insulin + prolactin + cortisol produced abundant milk-like secretory material in the alveolar lumen. RNA of the mammary gland after estradiol + progesterone priming or cultivation in the “growth-promoting” medium failed to show a measurable amount of casein mRNA activity when assayed in a cell-free protein synthesis system derived from Ehrlich ascites ribosomes, rabbit reticulocyte factors, and tRNA. However, the glands sequentially cultivated in the “growth-promoting” and the “lactogenic” media showed a high level of casein mRNA activity in the heterologous cell-free protein synthesis system. Sodium dodecyl sulfate/polyacrylamide gel electrophoretic characteristics of the immunoprecipitable (by antibody to mouse milk casein) polypeptides directed by the mammary RNA induced in organ culture medium containing the lactogenic hormones were similar to the characteristics of the polypeptides directed by mammary polysomes of lactating mice. These results demonstrate hormonal induction of a specific mRNA in a sequential two-step culture of an entire organ in a serum-free chemically defined medium.
Spontaneous mutation rates at enzyme loci in Drosophila melanogaster.
Authors: Mukai T , Cockerham C C
Published: May 2006

In a marked-inversion-balanced lethal system mutations were accumulated at a minimum pressure of natural selection on 2000 second chromosomes of Drosophila melanogaster that originated from 4 stem chromosomes. Five enzyme loci were tested: alpha-glycerol-3-phosphate dehydrogenase (EC 1.1.1.8), malate dehydrogenase (Mdh, EC 1.1.1.37), alcohol dehydrogenase (EC 1.1.1.1), hexokinase-C (Hex-C tentative name), and alpha-amylase (Amy, EC 3.2.1.1). Three band-morph mutants, one at the Mdh locus, one at the Hex-C locus, and one at the Amy locus, were detected out of 1,658,308 allele replications. In addition, 17 null mutants were found. Accepting that the number of structural genes is the same as that of bands in the salivary gland chromosomes, the total mutation rate per generation for all the structural genes in the second chromosomes is estimated to be 0.008-0.040, which is much smaller than that estimated for viability polygenes (0.12-0.17). Thus, it is speculated that most viability and other fitness polygenes are located in controlling regions outside the structural genes.
The intestine as a source of apolipoprotein A1.
Authors: Glickman R M , Green P H
Published: May 2006

The major apoprotein of rat mesenteric lymph chylomicrons has been isolated and characterized and shown to be identical to apoprotein A1 (apo A1) isolated from serum high density lipoprotein (HDL). During intestinal lipid absorption, active synthesis of apo A1 was demonstrated by radioactive amino acid incorporation into lymph chylomicron A1 as well as lymph HDL. Immunofluorescence studies of intestinal epithelium demonstrated a marked increase in apo A1 fluorescence, confirming an active synthesis of this apoprotein during lipid absorption. Quantitative immunoelectrophoretic methods were used to measure apo A1 in lymph and peripheral blood during various conditions designed to estimate the quantitative importance of intestinal apo A1 to the levels of circulating lipoproteins. During lipid feeding there was an increase in lymph apo A1 that was associated with lymph lipoproteins (50%) of density less than 1.006 g/ml whereas in basal lymph most apo A1 (85%) was in the lipoproteins of density greater than 1.006 g/ml. Lipid feeding in animals without lymph fistulas resulted in a significant increase in serum apo A1 levels; biliary diversion, designed to eliminate intestinal lipoproteins of density less than 1.006 g/ml, resulted in a significant decrease in serum apo A1 levels. These studies demonstrate that the intestine actively synthesizes apo A1 and is a significant source of this apoprotein for circulating lipoproteins.
A site-specific single-strand endonuclease from the eukaryote Chlamydomonas.
Authors: Burton W G , Roberts R J , Myers P A , Sager R
Published: May 2006

We have found a unique deoxyribonuclease in extracts of the eukaryotic green alga Chlamydomonas. When incubated with viral DNA from adenovirus-2, this enzyme produces discrete fragments that form bands upon electrophoresis in an agarose gel. Site specificity of the enzymatic cleavage examined by identifying the 5'-terminal nucleotides in cleaved adenovirus-2 DNA and by studies with synthetic polynucleotides of defined sequence, indicates that the initial endonucleolytic cleavage occurs at a site containing a deoxythymidine residue. Electron microscopy of cleaved adenovirus-2 DNA revealed single-strand segments within duplex DNA. We propose that the enzyme acts by making initial site-specific single-strand incisions, followed by subsequent excision on the same strand, producing a gapped duplex molecule; and that double-strand scissions result from limited occurrence of overlapping single-strand gaps on complementary strands.
DNA or RNA priming of bacteriophage G4 DNA synthesis by Escherichia coli dnaG protein.
Authors: Wickner S
Published: May 2006

Escherichia coli dnaG protein is involved in the initiation of DNA synthesis dependent on G4 or ST-1 single-stranded phage DNAs [Bouche, J.-P., Zechel, K & Kornberg, A. (1975) J. Biol. Chem. 250, 5995-6001]. The reaction occurs by the following mechanism: dnaG protein binds to specific sites on the DNA in a reaction requiring E. coli DNA binding protein. An oligonucleotide is synthesized in a reaction involving dnaG protein, DNA binding protein, and DNA. With G4 DNA this reaction requires ADP, dTTP (or UTP), and dGTP (or GTP). Elongation of the oligonucleotide can be catalyzed by DNA polymerase II or III in combination with dnaZ protein and DNA elongation factors I and III, presumably by the mechanism previously reported [Wickner, S. (1976) Proc. Natl. Acad. Sci. USA 73, 3511-3515] or by DNA polymerase I.
Method for obtaining a high resolution protein map starting from a low resolution map.
Authors: Agarwal R C , Isaacs N W
Published: May 2006

A method is described for estimating the phases of high resolution single-crystal diffraction data from proteins, by using as a starting point a set of low resolution phases (about 3 A) derived by multiple isomorphous replacement (or other) methods. The method consists in refining by least-squares the positions and thermal parameters of a set of dummy atoms placed in the initial low resolution electron density map, so as to minimize the discrepancy between the calculated scattering intensities and the scattering intensities observed in the high resolution data set. Phases calculated from these refined atomic positions are used to extend the resolution and to improve the quality of the electron density map. The success of the method depends on a new least-squares algorithm that has a radius of convergence of about 0.75 A. This large radius of convergence, together with the severe restrictions placed on the initial positions of the dummy atoms by the requirement that they lie within limited regions of the isomorphous electron density map, and the constraint imposed by the polymeric nature of a polypeptide chain account for the success of the method. The method has been successfully used to phase the structure factors of 2-zinc insulin at a resolution of 2 A and 1.5 A, starting from a set of isomorphous phases at 3-A resolution.
Thermosensitive step associated with transfer of the Ti plasmid during conjugation: Possible relation to transformation in crown gall
Authors: Tempé Jacques , Petit Annik , Holsters Marcelle , Montagu Marc van , Schell Jeff
Published: May 2006

It is reported here that transfer by means of a conjugative process of an oncogenic plasmid from a virulent strain of
Agrobacterium tumefaciens
to a strain of that organism that had been cured of the plasmid is thermosensitive. Since the thermosensitive step found in the conjugative process appears similar in every respect to a thermosensitive step that is involved in the transformation of a normal cell to a tumor cell in the crown gall disease of plants, it is suggested that the observed results may reflect the existence of a thermosensitive step that is common to these two processes.
Protease effects on specific growth properties of normal and transformed baby hamster kidney cells.
Authors: Brown M , Kiehn D
Published: May 2006

We have tested the effects of exogenous proteases on the growth of normal and transformed hamster fibroblasts in the classic culture assays for transformation. The results indicate that exogenous proteases act to decrease the serum requirement of normal cells but not nearly to the extent that occurs in the process of viral transformation. Proteases do not further decrease the serum requirement of transformed cells, nor do they affect the maximal saturation density or the plating efficiency in soft agar of either normal or transformed cells. Under conditions optimal for growth stimulation, proteases decrease the strength of cell-to-substrate adhesion but do not affect cellular morphology. In contrast to previous studies, experiments using highly purified trypsin and several different active-site inhibitors strongly suggest that the growth-stimulatory activity of trypsin is not directly related to the proteolytic activity of the molecule.
Tumor promoters inhibit spontaneous differentiation of Friend erythroleukemia cells in culture.
Authors: Rovera G , O'Brien T G , Diamond L
Published: May 2006

Clones of Friend erythroleukemia cells, characterized by the presence of 40-70% benzidine-positive cells synthesizing hemoglobin in the absence of inducing drugs, were treated with several phorbol diesters with a known range of tumor-promoting activity on mouse skin. Good correlation was found between the reported tumor-promoting activity of a particular phorbol diester and its ability to inhibit spontaneous erythroid differentiation in culture. The inhibition of differentiation by 12-O-tetradecanoyl-phorbol-13-acetate, the most active tumor promoter, was maximum after 4 days of treatment; this inhibition was reversed by removal of the phorbol diester no matter how long the period of treatment. Unlike control cells, which gradually revert to a population with a low percentage of benzidine-positive cells, cells treated with 12-O-tetradecanoyl-phorbol-13-acetate retained a high potential for spontaneous differentiation.
Specific changes in the collagen phenotype of BALB 3T3 cells as a result of transformation by sarcoma viruses or a chemical carcinogen
Authors: Hata Ryu-ichiro , Peterkofsky Beverly
Published: May 2006

Radioactive proline-labeled procollagen, accumulated during a 3-hr incubation of normal and transformed BALB 3T3 cultures, was treated with pepsin and the resulting collagen components were analyzed by carboxymethyl-cellulose chromatography and sodium dodecyl sulfate/polyacrylamide gel electrophoresis in the presence or absence of reducing agent. Collagen in the medium of three subclones of BALB 3T3 A-31 that exhibited contact-inhibition of growth at confluence, as well as in the medium of one that did not, consisted of α
1
and α
2
subunits in the ratio of 3:1, suggesting that 3T3 cells synthesize type I collagen, [α
1
(I)]
2
α
2
, and another type, which we have designated X, composed of α
1
chains, which may or may not be identical to α
1
(I). Culture medium from 3T3 transformed by Kirsten or Moloney sarcoma virus contained type I collagen and another type differing from I and X and designated as type Y. The latter appeared to be similar to type III collagen [α
1
(III)]
3
, since it contained intrahelical disulfide bonds. Analysis of intracellular collagen also demonstrated the presence of type III in Ki-3T3 and its absence from 3T3 cells. Collagen components from the medium of a simian virus 40 transformant were identical to those of the contact-inhibited clones, while the collagen from a 4-nitroquinoline-1-oxide-induced transformant was composed mainly of two components differing from α
1
(I), α
2
, or α
1
(III). These results suggest that the type of collagen accumulated in transformed cell cultures may be specifically related to the transforming agent.
Immunohistochemical localization in rabbit brain of a peptide resembling the COOH-terminal octapeptide of cholecystokinin.
Authors: Straus E , Muller J E , Choi H S , Paronetto F , Yalow R S
Published: May 2006

Immunohistochemical techniques were used to demonstrate the presence of a material resembling the COOH-terminal octapeptide of cholecystokinin in rabbit cerebral cortical neurons. Deep staining was seen in cell bodies throughout the cortical grey matter and diffusely in the subcortical white matter.
Analysis of polyoma virus nuclear RNA by mini-blot hybridization.
Authors: Birg F , Favaloro J , Kamen R
Published: May 2006

The size and sequence composition of virus-specific RNA extracted from the nuclei of mouse cells late during polyoma virus productive infection were studied by blot-hybridization analysis of 32P-labeled RNA fractionated on CH3HgOH/agarose gels. Viral RNA molecules between approximately 0.4 and 4 times the length of a complete transcript of the 5.4-kilobase circular viral DNA were found. Less than 20% of such molecules were polyadenylylated. Although viral RNA of all sizes contained species that together hybridized to the entire polyoma genome, sequences complementary to the late region were more abundant than sequences complementary to the early region in transcripts less than 10-12 kilobases long.
Enzyme associations in T4 phage DNA precursor synthesis
Authors: Reddy G. P. V. , Singh A. , Stafford M. E. , Mathews C. K.
Published: May 2006

A direct approach is described to the question: Are enzymes of DNA precursor synthesis organized into a supramolecular structure? This approach involved sedimentation analysis of several T4 phage-coded early enzyme activities in crude lysates of infected
Escherichia coli
. One-third to one-half of several activities tested—dCMP hydroxymethylase, dTMP synthetase, deoxynucleoside 5′-monophosphate kinase, deoxyuridine triphosphatase, and probably dCMP deaminase, but
not
dihydrofolate reductase or DNA polymerase—sedimented much more rapidly than expected from molecular weight. About 5% of the host cell nucleoside diphosphate kinase, known to participate in T4 DNA precursor synthesis, cosedimented with these activities. To show that this rapidly sedimenting material represents an organized enzyme complex rather than a nonspecific aggregate, we studied the kinetics of formation of dTTP with dUMP as the initial substrate. This three-step reaction sequence reached its maximal rate within a few seconds when catalyzed by enzymes in the aggregate, whereas an equivalent mixture of uncomplexed enzymes required nearly 20 min before dTTP synthesis reached its maximal rate. The effect of aggregation is evidently to decrease the volume into which intermediates are free to diffuse. Because there is reason to believe that intracellular concentration gradients of DNA precursors exist, the properties of this enzyme aggregate
in vitro
may help to explain how such gradients are maintained.
Cleavage specificity of the restriction endonuclease isolated from Haemophilus gallinarum (Hga I).
Authors: Brown N L , Smith M
Published: May 2006

The nucleotide sequences in the replicative form (duplex) of phiX174 DNA around six sites cut by Hga I, a restriction endonuclease from Haemophilus gallinarum, have been compared. The enzyme produces a staggered cleavage resulting in a pentanucleotide 5'-terminal extension. The sequences within and immediately surrounding the pentanucleotide cleavage site have no obvious relationship. However, the sequence 5'-G-A-C-G-C-3' 3'-C-T-G-C-G-5' occurs five nucleotide pairs to the left of the cut in the upper strand and 10 nucleotide pairs to the left of the cut in the lower strand and, therefore, is believed to constitute the recognition site. This is a member of the class of restriction endonucleases in which recognition and cleavage sites lack 2-fold rotational symmetry. The method used to define the cleavage site is of general applicability.
Crystallographic studies of bovine beta2-microglobulin.
Authors: Becker J W , Ziffer J A , Edelman G M , Cunningham B A
Published: May 2006

Crystals of the bovine milk protein lactollin yield x-ray diffraction data extending to a resolution of 2.8 A. Lactollin is a bovine analogue of beta2-microglobulin, a protein that is homologous in amino acid sequence to the constant domains of immunoglobulins and is the light chain of the human and murine major histocompatability antigens. The protein crystallizes in the orthorhombic space group P2(1)2(1)2(1) with a = 77.4, b = 47.9, and c = 34.3 A. The unit cell parameters and physical chemical solution studies indicate that the molecule exists in the crystal and in solution as a single polypeptide chain of 12,000 daltons.
Evidence against phospholipid asymmetry in intracellular membranes from liver.
Authors: Sundler R , Sarcione S L , Alberts A W , Vagelos P R
Published: May 2006

We have studied the distribution of phospholipids across the membrane of microsomal vesicles and Golgi-derived secretory vesicles from rat liver by the use of phospholipases. Model studies on single-bilayer phospholipid vesicles showed that phospholipase A2 (phosphatide 2-acyl-hydrolase, EC 3.1.1.4) cleaved at least 80% of the lipids on the outer surface of such vesicles without significant attack on the inner surface. In microsomal vesicles approximately 40% of the outer surface phospholipids were cleaved before the enzyme gained access to the interior of the vesicles. The same conclusion was reached for Golgi vesicles. By following the degradation of the three major phospholipids in intact microsomes and in extracted lipids we found that the same fraction of each of these phospholipids was exposed on the outer surface of the microsomal vesicles. Corresponding experiments with Golgi vesicles showed that distinctly different fractions of phosphatidylcholine and phosphatidylethanolamine were present on the surface of these vesicles. However, the difference was accounted for by enrichment of phosphatidylcholine in intravesicular particles rather than by asymmetry across the vesicle membrane. The results from specific hydrolysis of phosphatidylinositol confirmed an essentially symmetric distribution of this phospholipid across the microsomal and the Golgi vesicle membranes.
Ionic requirements for induction of maturation (meiosis) in full-grown and medium-sized Xenopus laevis oocytes.
Authors: Baltus E , Hanocq-Quertier J , Pays A , Brachet J
Published: May 2006

There is already good evidence that calcium ions are involved in the induction of maturation in full-grown amphibian oocytes; we show here that other cations (K+, Mg2+) also play a role in this process. Full-grown (1.3 mm in diameter) and medium-sized (0.8-1.0 mm in diameter) oocytes were compared in the present study. It was found that, provided the medium is K+-free, valinomycin induces maturation in full-grown, but not in medium-sized, oocytes. Increasing the CaCl2 (20 mM) or the MgSO4 (40 mM) content of the medium induces maturation in full-grown, but not in medium-sized, oocytes; however, the latter undergo germinal vesicle breakdown after treatment with either progesterone or ionophore A23187 if there is an excess of Ca2+ or Mg2+ in the medium. Maturation is possible in a Na+-free medium, but amiloride inhibits germinal vesicle breakdown when NaCl is present in the medium. It is concluded that maturation is controlled by changes in the balance between the various ions rather than by Ca2+ alone.
Transfer of codominant markers by isolated metaphase chromosomes in Chinese hamster ovary cells.
Authors: Spandidos D A , Siminovitch L
Published: May 2006

Codominant mutations to methotrexate and ouabain resistance in Chinese hamster ovary cells can be transferred to recipient Chinese hamster ovary cells by isolated metaphase chromosomes. For methotrexate, both the structural change and the increased activity of dihydrofolate reductase (5,6,7,8-tetrahydrofolate:NADP+ oxidoreductase EC 1.5.1.3), characteristic of the donor cells, are observed in the transferents (cells that carry and express functions derived by chromosome transfer). The transferents are unstable in the absence of selection although stable clones can be isolated. From results obtained by fractionation of chromosomes and transfer to recipients, the methotrexate and ouabain markers can be assigned to the middle and large size-classes of chromosomes, respectively. By fractionation and transfer of chromosomes, from transferents to new recipients, evidence has been obtained that chromosome integration is not restricted to a particular chromosomal site in the recipient.