bluuebunny/crossref_metadata_2025 huggingface dataset:
cDNA clone coding for part of a mouse H-2d major histocompatibility antigen.
Authors: Kvist S , Bregegere F , Rask L , Cami B , Garoff H , Daniel F , Wiman K , Larhammar D , Abastado J P , Gachelin G , Peterson P A , Dobberstein B , Kourilsky P
Published: May 2006

mRNA coding for mouse major transplantation antigens of the d haplotype was partially purified, copied into double-stranded cDNA, and cloned in Escherichia coli. Clones were selected by their ability to hybridize specifically with mRNA coding for H-2K, D, or L antigens. One of these clones, pH-2d-1, carries a 1200-base-pair insert, comprising the noncoding region, including poly(A) at the 3' end and part of the coding region. A partial sequence of the latter region showed extensive homology with the known amino acid sequences of H-2Kb,Kk, and HLA-B7 antigens. From this comparison, it appears that the coding region extends from amino acid 133 in the second domain, through the third domain, to the cytoplasmic COOH-terminal region. A stretch of 24 hydrophobic or uncharged residues, located 31 amino acids from the COOH-terminal end, could represent the segment that spans the membrane. This is followed on the cytoplasmic side of the membrane by a cluster of basic amino acids and a possible phosphorylation site on a threonine residue.
Ovine prolactin: equilibrium characteristics of the recombinant molecule formed by noncovalent interaction of two fibrinolysin fragments by fluorescence polarization.
Authors: Jibson M D , Li C H , Glaser C B
Published: May 2006

The equilibrium characteristics of the recombined molecule formed by noncovalent interaction of two fibrinolysin fragments of ovine prolactin (oPRL) have been studied with fluorescence polarization. Fluorescein isothiocyanate (isomer I) was used to label oPRL-(1-53), creating a fluorescent peptide indistinguishable from the unlabeled fragment in the complementation reaction with oPRL-(54-199). The dissociation constant of the recombinant prolactin was 0.144 microM at 30 degrees C, with a free energy of dissociation of 9.50 kcal/mol.
Target cell specificity of two species of human interferon-alpha produced in Escherichia coli and of hybrid molecules derived from them.
Authors: Streuli M , Hall A , Boll W , Stewart W E , Nagata S , Weissmann C
Published: May 2006

Plasmids containing cDNAs for human interferon (IfN) alpha-1, IFN alpha-2, and several hybrids of the two cDNAs, all joined identically to an Escherichia coli lac promoter fragment gave rise, in E. coli, to fused interferons (fIFNs) that had very different target-cell specificities. fIFN alpha-1 had a lower specific activity on human WISH cells than on bovine MDBK cells, while fIFN alpha-2 showed the opposite behavior. fIFN hybrids with the NH2-proximal half of fIFN alpha-2 behaved qualitatively like fIFN alpha-1, and those with the NH2-proximal half of fIFN alpha-2, behaved like fIFN alpha-2. On mouse L929 cells, fIFN alpha-2 was almost inactive, while fIFN alpha-1 showed relatively high activity. In this case, the fIFN hybrids with the COOH-proximal half of IFN alpha-1 showed activity on mouse cells, while the reciprocal hybrid did not. In many cases, the activity spectrum of the hybrids was very different from that of either parent. We propose that the IFN molecule has either two binding sites or two regions constituting the binding site, one in the COOH- and the other in the NH2-proximal half. The experimental findings can be accounted for if the fits of the two sites to their receptor counterparts on different cell lines are independent of one another.
Dynamic protein structures: infrared evidence for four discrete rapidly interconverting conformers at the carbon monoxide binding site of bovine heart myoglobin.
Authors: Caughey W S , Shimada H , Choc M G , Tucker M P
Published: May 2006

Infrared spectra for the carbon monoxide complex with myoglobin isolated as the oxygenyl species from bovine heart muscle were carefully examined in the C--O stretch region as either the pH or the temperature was varied. Deconvolutions of these spectra into bands of Gaussian shape suggest the presence of four bands near 1938(I), 1944(II), 1954(III), and 1965(IV) cm-1 with halfband widths of about 18, 9, 9, and 10 cm-1, respectively. The relative intensities of the four bands varied with changes in pH or temperature. 13C NMR spectra and other evidence indicate that the four C--O stretch bands arise from four discrete rapidly interconverting conformers: CI, CII, CIII, and CIV. Under conditions of physiological pH and temperature, the relative stabilities are CI approximately CII much greater than CIII approximately CIV. The delta H and delta S values for conformer interconversions are estimated to range from -8 to 34 kJ/mol and -27 to 87 J.mol-1 K-1, respectively; therefore the structures of the conformers may be expected to vary significantly. These findings provide evidence for a highly flexible, dynamic structure at the ligand-binding site of bovine myoglobin, even when ligands are bound.
Monomeric chlorophyll
a enol
: Evidence for its possible role as the primary electron donor in photosystem I of plant photosynthesis
Authors: Wasielewski Michael R. , Norris James R. , Shipman Lester L. , Lin Chih-Ping , Svec Walter A.
Published: May 2006

The chlorophyll
a
(Chl
a
) special-pair model of the primary donor of photosystem I (P700) does not account in a completely adequate fashion for the magnetic resonance properties observed for P700
+
. Moreover, P700 is at least 420 mV easier to oxidize than is Chl
a in vitro
. Neither Chl
a
dimer formation nor selective ligation of Chl
a
can account for this potential difference. Enolization of the Chl
a
ring V β-keto ester results in a very different π electronic structure. The Chl
a enol
can be trapped as a silyl
enol
ether. In addition, the
enol
analog 9-desoxo-9,10-dehydro-Chl
a
can be prepared. Both the trapped
enol
and its 9-H analog are ≈350 mV easier to oxidize than Chl
a
. The ESR spectrum of the cation radical consists of a single 6.1-G gaussian line that is line narrowed relative to that of Chl
a
+
in a manner similar to P700
+
. Electron-nuclear double resonance (ENDOR) spectroscopy resolves only a 3.5-MHz hyperfine splitting for the 3-methyl-group. The remaining splittings are all less than 3.5 MHz. The second moment of the ESR line of fully
13
C-enriched 9-desoxo-9,10-dehydro-Chl
a
+
agrees with that of [
13
C]P700
+
to within 10%. Application of the special-pair model to the [
13
C]P700
+
second-moment data yields a 100% error.
Ab initio
molecular orbital calculations on ethyl chlorophyllide
a enol
cation bear out the ESR and ENDOR data. We conclude that a monomeric Chl
a enol
model provides a better description of the magnetic resonance parameters and oxidation potential of P700 than a Chl
a
special-pair model.
Presence of autoantibody for phospholipase inhibitory protein, lipomodulin, in patients with rheumatic diseases.
Authors: Hirata F , del Carmine R , Nelson C A , Axelrod J , Schiffmann E , Warabi A , De Blas A L , Nirenberg M , Manganiello V , Vaughan M , Kumagai S , Green I , Decker J L , Steinberg A D
Published: May 2006

The activity of phospholipase inhibitory protein, lipomodulin, partially purified from rabbit neutrophils, was markedly decreased after treatment with sera from patients with rheumatic diseases such as systemic lupus erythematosus, rheumatoid arthritis, and dermatomyositis. The decrease of the protein's inhibitory activity on phospholipase A2 paralleled the amount of [35S]methionine-labeled lipomodulin precipitated by the sera. Absorption of patients' sera with anti-human IgM (mu chain) or protein A-agarose, but not with anti-human IgG (gamma chain), decreased their ability to decrease the activity of lipomodulin on phospholipase A2 or to precipitate the radioactive lipomodulin. The IgM fraction of patients' sera could precipitate [35S]methionine-labeled lipomodulin (40,000 daltons) which comigrated with highly purified lipomodulin on gel electrophoresis with sodium dodecyl sulfate. All of these observations suggest that the sera of many patients with rheumatic diseases contain autoantibody against lipomodulin. A monoclonal antibody against lipomodulin was also obtained. Stimulating human fibroblasts with bradykinin in the presence of monoclonal antilipomodulin antibody markedly enhanced arachidonic acid release due to the activation of phospholipase(s) in the intact cells, and this stimulatory effect was blocked by adding purified lipomodulin. These findings suggest that lipomodulin regulates the activity of phospholipase(s) on the cell surface and that autoantibodies against lipomodulin may play a role in certain symptoms of rheumatic diseases, especially by the formation of prostaglandins and other metabolites of arachidonic acid.
A spectrum of monoclonal antibodies reactive with human mammary tumor cells.
Authors: Colcher D , Hand P H , Nuti M , Schlom J
Published: May 2006

Splenic lymphocytes of mice, immunized with membrane-enriched fractions of metastatic human mammary carcinoma tissues, were fused with the NS-1 non-immunoglobulin-secreting murine myeloma cell line. This resulted in the generation of hybridoma cultures secreting immunoglobulins reactive in solid-phase radioimmunoassays with extracts of metastatic mammary carcinoma cells from involved livers, but not with extracts of apparently normal human liver. As a result of further screening of immunoglobulin reactivities and double cloning of cultures, 11 monoclonal antibodies were chosen that demonstrated reactivities with human mammary tumor cells and not with apparently normal human tissues. These monoclonal antibodies could be placed into at least five major groups on the basis of their differential binding to the surface of various live human mammary tumor cells in culture, to extracts of mammary tumor tissues, or to tissue sections of mammary tumor cells studied by the immunoperoxidase technique. Whereas a spectrum of reactivities to mammary tumors was observed with the 11 monoclonal antibodies, no reactivity was observed to apparently normal cells of the following human tissues: breast, lymph node, lung, skin, testis, kidney, thymus, bone marrow, spleen, uterus, thyroid, intestine, liver, bladder, tonsils, stomach, prostate, and salivary gland. Several of the antibodies also demonstrated a "pancarcinoma" reactivity, showing binding to selected non-breast carcinomas. None of the monoclonal antibodies showed binding to purified ferritin or carcinoembryonic antigen. Monoclonal antibodies of all five major groups, however, demonstrated binding to human metastatic mammary carcinoma cells both in axillary lymph nodes and at distal sites.
A highly potent 3200-dalton adrenal opioid peptide that contains both a [Met]- and [Leu]enkephalin sequence.
Authors: Kilpatrick D L , Taniguchi T , Jones B N , Stern A S , Shively J E , Hullihan J , Kimura S , Stein S , Udenfriend S
Published: May 2006

A 3200-dalton adrenal enkephalin-containing peptide, designated peptide E, that exhibits high opiate activity in the guinea pig ileum longitudinal muscle preparation was purified, and its structure was determined. It contains an amino-terminal [Met]enkephalin sequence and a [Leu]enkephalin sequence at the carboxyl terminus. Sequence analysis revealed that peptide E arises from a previously characterized 4900-dalton adrenal enkephalin-containing peptide. Peptide E was shown to be 30 times more potent than [Met]enkephalin in the guinea pig ileum assay, which suggests that the adrenal enkephalin-containing peptide may perform a unique biological function in vivo.
Lesion distribution, multiple infection, and the logistic increase of plant disease
Authors: Waggoner Paul E. , Rich Saul
Published: May 2006

The lesions of few of the 112 observed cases of plant disease were randomly distributed; most were fitted by the negative binomial function with exponent ≈ 1. The proportion of healthy hosts generally equaled the frequency of zero in the negative binomial. The same course of an epidemic is calculated for the logistic increase of infected plants or for plants infected by propagules produced in proportion to lesions and distributed with exponent equal 1.
Enol-keto
tautomerism of α-ketophosphonates
Authors: Tam Coretta C. , Mattocks Karen L. , Tishler Max
Published: May 2006

A number of α-ketophosphonates have been prepared and their
enol-keto
tautomerism has been studied by means of proton and phosphorus NMR and infrared spectroscopy and the ferric chloride test. Aliphatic ketophosphonates exist largely in the
keto
tautomeric forms, with only a small amount of
enol
forms present. All the aromatic acylphosphonates studied, however, enolize extensively. An x-ray analysis confirmed enolization and
E
configuration as the only stereochemical isomer. Reaction of diazomethane with diethyl
p
-methoxyphenylacetyl phosphonate gave a mixture of
O
-methylation and carbene insertion products, whereas the same reaction with diethyl isobutyryl phosphonate gave only carbene insertion products.
Sulfation of a cell surface glycoprotein correlates with the developmental program during embryogenesis of Volvox carteri.
Authors: Wenzl S , Sumper M
Published: May 2006

A sulfated cell surface glycoprotein with an apparent molecular weight of 185,000 is synthesized in the multicellular organism Volvox only during the limited period of embryogenesis. The lifetime of sulfate residues on this glycoprotein is very short (half-life about 20 min). Production of this sulfated glycoprotein sharply decreases to a minimum shortly before the onset of the differentiating cell cleavage--e.g., in asexual development, before the 32-cell embryo divides. It is demonstrated that the sulfated glycoprotein behaves in many respects as would the hypothetical cell surface component postulated by a recently published model [Sumper, M. (1979) FEBS Lett. 107, 241-246], which proposes an explanation for the cell-counting mechanism and the spatial control of differentiation that is operative in Volvox embryogenesis.
Gene number in species of Astereae that have different chromosome numbers
Authors: Gottlieb L. D.
Published: May 2006

Differences in the gametic chromosome numbers (
n
= 4, 5, 9) of species in the Astereae tribe of the Compositae have been variously interpreted. One hypothesis proposes that
n
= 9 was the original base number of the group and that the lower numbers resulted from aneuploid reduction. The alternative hypothesis asserts that the ancestral base number was
n
= 4 or
n
= 5 and that species in which
n
= 9 are allotetraploids derived by hybridization between taxa with the lower numbers. Electrophoretic analysis of 17 enzyme systems in five species of
Machaeranthera
, in which
n
= 4, 5, and 9, and two species of
Aster
in which
n
= 5 and 9, demonstrates that all of these species have the same number of gene loci specifying the tested enzymes. The absence of isozyme multiplicity in the species in which
n
= 9 suggests that they did not arise by polyploidy.
Preferential mating in symmetric multilocus systems
Authors: Raper John , Karlin Samuel
Published: May 2006

A class of multilocus models that incorporate both preferential mating and viability selection is studied. Symmetry in alleles is supposed, resulting in the phenotypes being dependent only on the location of heterozygous loci. Otherwise, an arbitrary number of loci, number of alleles per locus, and arbitrary recombination schemes, viability parameters, and preferential mating pattern are allowed. The conditions for stability of a central polymorphism,
c
*
, are indicated and interpreted. Mating and viability parameters enter as one combined quantity for each phenotypic class, which represents a generalized fitness. The effect on stability of
c
*
of increasing the number of alleles per locus and the number of loci requires the formulation to be set in terms of frequency-dependent preference parameters.
Physical and genetic characterization of the glnA--glnG region of the Escherichia coli chromosome.
Authors: Backman K , Chen Y M , Magasanik B
Published: May 2006

We have cloned and characterized a fragment of the Escherichia coli chromosome spanning glnA, the structural gene for glutamine synthetase (L-glutamate:ammonia ligase (ADP-forming), EC 6.3.1.2]. The fragment also carriers glnG, whose product is necessary for regulation of glnA expression, and a previously unidentified gene whose function we have not discovered. Transcription of glnA and the newly identified gene occurs divergently from a region between the two genes. Transcription of glnA proceeds toward glnG, which is transcribed in the same direction. A region of DNA between glnA and glnG contains genetic information whose loss may result in the inability to reduce expression of glnA and other operons in response to ammonia (the GlnC phenotype).
Complete amino acid sequence of variable domains from two monoclonal human anti-gamma globulins of the Wa cross-idiotypic group: suggestion that the J segments are involved in the structural correlate of the idiotype.
Authors: Andrews D W , Capra J D
Published: May 2006

The complete amino acid sequences of the variable regions of two human IgM anti-gamma globulins are reported. The two proteins, Sie and Wol, share idiotypic determinants that are distinct from those shared by the two previously sequenced IgM anti-gamma globulins, Lay and Pom [Capra, J. D. & Kehoe, J. M. (1974) Proc. Natl. Acad. Sci. USA 71, 4032-4036; Klapper, D. G. & Capra, J. D. (1976) Ann. Immunol. (Inst. Pasteur) 127C, 261-271.] In contrast to Lay and Pom, Sie and Wol have very little homology in the complementarity-determining hypervariable regions of either their light or heavy polypeptide chains. However, there are only two amino acid differences in the framework portions of the light chains, and the J segments of both chains are homologous. These data suggest that the predominant idiotypic determinant in this cross-idiotypic system may be different than in the Po group and may be either related to their light chain framework structures or to the amino acid sequence in the J segments of these molecules.
Gustin concentration changes relative to salivary zinc and taste in humans.
Authors: Shatzman A R , Henkin R I
Published: May 2006

Biochemical characteristics of gustin, the major zinc protein in human parotid saliva, are similar whether the protein is isolated from subjects with normal taste acuity or from patients with hypogeusia (who may have a little as 1/5th as much parotid saliva gustin as normal subjects do). Zinc concentration in fraction II of parotid saliva, the fraction in which gustin is found on Sephadex G-150 or Sephacryl S-200 column chromatography, is proportional to the gustin content of saliva and is decreased in patients with lower than normal total parotid saliva zinc. The quantity and spectrophotometric indices of all other protein fractions isolated from patients by these column chromatographic techniques did not differ from those of normals. One patient with proven hypogeusia and low concentrations of zinc in total parotid saliva and fraction II, after 9 days of treatment with exogenous zinc, showed a 150% increase in fraction II zinc and a concomitant increase in apparent gustin levels; these changes preceded the return of normal taste function. These data demonstrate that zinc treatment can affect both taste and gustin concentrations in hypogeusia.
Ageing of α-chymotrypsin: Cannibalistic and hydroxide ion reactions
Authors: Wu Hua-Lin , Wastell Andrea , Bender Myron L.
Published: May 2006

The loss of catalytic activity (irreversible denaturation) of α-chymotrypsin (EC 3.4.21.1) as a function of pH between 6 and 13 is described. Around neutrality the irreversible denaturation is second order with respect to enzyme. At high pH, the irreversible denaturation is first order with respect to enzyme and also with respect to hydroxide ion. The first- or second-order dependency on enzyme concentration has been shown both by the time course of denaturation and by the effect of enzyme concentration on the rate of denaturation. The first-order dependency on hydroxide ion was shown by a plot of the logarithm of the rate constant vs. pH. These enzyme inactivations are peptide bond cleavages at all pH values. From the kinetics, the irreversible denaturation can be described as a cannibalistic reaction of two enzyme molecules around neutrality or as a reaction of one enzyme molecule plus one hydroxide ion at high pH.
Multiple conformations at functional site of hemerythrin: Evidence from resonance Raman spectra
Authors: Duff Lori L. , Klippenstein Gerald L. , Shriver Duward F. , Klotz Irving M.
Published: May 2006

Resonance Raman spectra were obtained for monomeric oxymyohemerythrin and for the azide, thiocyanate, cyanate, cyanide, and fluoride adducts of metmyohemerythrin. The internal ligand vibrations in these complexes appear at essentially the same frequencies as those in the corresponding complexes of octameric hemerythrin. Likewise the Fe—O frequencies in H
2
16
O do not depend on quaternary structure of the protein. The anionic adducts fall into two classes in regard to isotope exchange behavior in H
2
18
O. They also manifest a novel photochemical transformation from one class of exchange behavior to the other. It seems evident that the functional site in hemerythrin exists in at least two different conformational states and that irradiation can stimulate isotope exchange in the exchange-resistant form.
Opiates inhibit adenylate cyclase by stimulating GTP hydrolysis.
Authors: Koski G , Klee W A
Published: May 2006

Specific, GTP hydrolysis catalyzed by membranes prepared from neuroblastoma--glioma (NG108-15) hybrid cells can be measured in the presence of adenosine-5'-[beta, gamma-imido] triphosphate (p[NH]ppA), ATP, and a nucleotide triphosphate-regenerating system. Opiates and opioid peptides stimulate low Km GTP hydrolysis when measured in the presence of Na+ and Mg2+. Opiate stimulation is rapid, stereospecific, and reserved by the antagonist naloxone. Potencies of opiates as stimulators of GTP hydrolysis and as inhibitors of adenylate cyclase are closely correlated. Agents that stimulate adenylate cyclase, including prostaglandin E1, 2-Cl-adenosine, secretin, and NaF, have little or no effect upon the rate of GTP hydrolysis. Opiates have no effect upon either adenylate cyclase or GTPase activity in membranes prepared from C6-BU1 glioma cells, which lack opiate receptors. In view of the pivotal role of GTP in the activation of adenylate cyclase, we conclude that receptor-mediated stimulation of GTP hydrolysis is the mechanism by which opiates and other inhibitory hormones lower adenylate cyclase activity in NG108-15 cell membranes.
Alcohol and polyol dehydrogenases are both divided into two protein types, and structural properties cross-relate the different enzyme activities within each type.
Authors: Jörnvall H , Persson M , Jeffery J
Published: May 2006

Sorbitol dehydrogenase from sheep liver shows similarities to mammalian and yeast alcohol dehydrogenases. Comparisons based on peptides from segments of sorbitol dehydrogenase reveal that homologous regions with 38% identity include two ligands to the active site zinc atom in liver alcohol dehydrogenase, as well as further important residues. Similarities in in other regions are less extensive, exactly as they are between different alcohol dehydrogenases. In all aspects, sorbitol dehydrogenase appears as a typical member of the alcohol dehydrogenase family. On the other hand, alcohol dehydrogenase from Drosophila, which has a shorter subunit, is not closely related to either of these enzymes, except for a region that probably corresponds to the first part of the coenzyme binding domain in many dehydrogenases. Instead, Drosophila alcohol dehydrogenase in its supposed catalytic region shows similarities toward Klebsiella ribitol dehydrogenase, which also has a small subunit. It may be concluded that both alcohol and polyol dehydrogenases show two types of protein subunit, reflecting an early subdivision of polypeptide types into "long" and "short" subunits rather than into different enzymatic specificities or quaternary structures. The relationships explain known properties of all these enzymes and provide insight into functional mechanisms and evolutionary interpretations.
Active gene sequences are undermethylated.
Authors: Naveh-Many T , Cedar H
Published: May 2006

The degree of methylation of active regions of the chromosome has been investigated by several techniques. DNase I (deoxyribonuclease I, EC 3.1.21.1) was used to introduce nicks in the active regions of the nucleus and thereby specifically label these areas. By using the methylation-specific restriction enzymes Hpa II and Hha I it could be shown that active genes are more sensitive to these probes than are other parts of the genome. In order to measure the amount of methylation at all CpG residues, DNA was nick-translated in the presence of [alpha-32P]dGTP as the sole nucleotide source and the methylated cytosine was detected by the standard nearest-neighbor analysis. Using this assay, we found that about 70% of all CpG sequences in animal cell DNA are methylated. In active nuclear regions that are sensitive to DNase I, only 30-40% of the CpG residues are methylated. This method was also employed to study the gene sequences that are complementary to cellular RNA. By this criterion expressed gene sequences are only 20-30% methylated. These data suggest that undermethylation is a general phenomenon in all actively transcribed genes.
Pyochelin: novel structure of an iron-chelating growth promoter for Pseudomonas aeruginosa.
Authors: Cox C D , Rinehart K L , Moore M L , Cook J C
Published: May 2006

Pyochelin, an endogenous growth promoter that solubilizes ferric iron, has been isolated from Pseudomonas aeruginosa, including clinical strains. The structure of pyochelin has been assigned as 2-(2-o-hydroxyphenyl-2-thiazolin-4-yl)-3-methylthiazolidine-4-carboxylic acid and is of a different type from those previously assigned to siderophores (siderochromes) from bacteria. The assignment rests on 1H and 13C NMR data, high-resolution (including field desorption) mass spectrometry, and spectroscopic properties of synthetic model compounds. Pyochelin is presumed to be biosynthesized from salicylic acid and two moles of cysteine.
Selection of rat hepatoma cells defective in hormone-regulated production of mouse mammary tumor virus RNA.
Authors: Grove J R , Ringold G M
Published: May 2006

We have been studying the mechanism of glucocorticoid hormone action by using mouse mammary tumor virus (MMTV)-infected rat hepatoma cells as a model system. J2.17, a clonal cell line that contains one MMTV provirus, induces tyrosine aminotransferase (TyrATase; L-tyrosine:2-oxoglutarate aminotransferase, EC 2.6.1.5), viral RNA, and the cell surface viral glycoprotein gp52 in response to dexamethasone. Using a fluorescence-activated cell sorter and a rabbit antiserum directed against gp52, we selected a cell population that displays a reduced hormone-mediated increase in cell surface gp52. Fourteen clones of this population were assayed for induction of viral gp52 and RNA and of cellular TyrATase. The results of these assays revealed that the clones display a variety of responses to hormone. One clone has retained wild-type responses of both TyrATase and gp52. Six clones exhibit coordinately reduced or abolished responses of both markers. Seven clones show normal induction of TyrATase but reduced or undetectable induction of gp52. These latter clones exhibit reduced production of MMTV RNA and thus may represent a unique class of variants defective in the regulation of MMTV gene expression.
Functional unit of the low density lipoprotein receptor of fibroblasts: a 100,000-dalton structure with multiple binding sites.
Authors: Innerarity T L , Kempner E S , Hui D Y , Mahley R W
Published: May 2006

The low density lipoprotein (apoprotein B,E) receptors of fibroblasts bind plasma lipoproteins that contain either the B (apo-B) or E (apo-E) apoproteins. These include the low density lipoproteins (LDL) containing apo-B and certain high density lipoproteins containing apo-E (e.g., the cholesterol-induced apo-E HDLc). The same receptor binds both LDL and apo-E HDLc, but the apo-E HDLc bind with much higher affinity. This higher affinity is due to the binding of apo-E HDLc to multiple receptor sites. One possible structural model for this receptor is that each apo-B,E receptor possesses a single binding site. Thus, the multiple binding of apo-E HDLc would require the recruitment of four independent receptors to bind to a single apo-E HDLc particle. A second model is that each receptor unit possesses multiple binding sites capable of binding one apo-E HDLc particle or four LDL particles. This study characterizes the apo-B,E receptors in situ in the membranes of fibroblasts by radiation inactivation. This technique allows one to determine the functional size of the receptor on the basis of the amount of radiation required to inactivate the structure. The larger the molecular size of the structure, the less ionizing radiation (generated by a linear accelerator) that will be required to abolish the receptor--ligand interaction. The functional size of the apo-B,E receptor is 106,000 Mr as determined with both LDL and apo-E HDLc binding after radiation inactivation. Furthermore, the data derived from radiation inactivation and Scatchard analysis indicate that each apo-B,E receptor has multiple binding sites and that each functional receptor unit, capable of binding one apo-E HDLc or four LDL particles, has a molecular weight of 106,000.
Larval selectivity for yeast species by
Drosophila mojavensis
in natural substrates
Authors: Fogleman James C. , Starmer William T. , Heed William B.
Published: May 2006

The yeast flora found in the major substrates of
Drosophila mojavensis
and in larval guts was studied both qualitatively and quantitatively. Quantitative studies show that, in four of the five substrates tested, the larvae did not contain a random sample of the yeasts present in the substrates. One widely distributed cactus yeast,
Pichia cactophila
, was typically in greater frequency in the larvae than in the substrates. Another cactus yeast,
Candida sonorensis
, typically exhibited the opposite relationship. Laboratory tests support larval preference behavior rather than differential digestion as being primarily responsible. Larvae are capable of distinguishing between patches of different yeast species and spend more time in patches of preferred yeasts.
D. mojavensis
appear to be ecological (host plants) generalists and physiological (yeasts) specialists in contrast to the other cactophilic
Drosophila
. Selective feeding by
D. mojavensis
larvae in natural substrates may represent optimal foraging behavior.
Localization of the human insulin gene to the distal end of the short arm of chromosome 11.
Authors: Harper M E , Ullrich A , Saunders G F
Published: May 2006

The human insulin gene was mapped by hybridization in situ of 3H-labeled recombinant plasmid pHIG900 to chromosome preparations in the presence of 10% dextran sulfate. pHIG900 contains a 900-base pair insert of human genomic DNA that includes the coding region for the C peptide and intervening sequence 2. A significant percentage of hybridized cells (34%) exhibited silver grains on the distal end of the short arm (band p15) of chromosome 11. Furthermore, silver grains on this region represented 26% of all chromosomal label. These results demonstrate chromosomal localization of the human insulin gene to 11p15.
Synthesis of capped and uncapped methylated oligonucleotides by the virion transcriptase of spring viremia of carp virus, a rhabdovirus.
Authors: Gupta K C , Roy P
Published: May 2006

Capped and uncapped methylated oligonucleotides, five and six nucleotides in length, were synthesized in vitro in spring viremia of carp virus transcription reaction mixtures containing ATP + CTP, ATP + CTP + GTP, or ATP + CTP + UTP, but not in any other combinations of two or three ribonucleoside triphosphates. The oligonucleotides that have been characterized are consistent with the structures: m7GpppAmpNpCpNpN, GpppAmpNpCpNpN, pppAmpNpCpNpN, and ppAmpNpCpNpN--i.e., similar to those of the termini of transcripts made in complete reaction mixtures. Because both capped and uncapped methylated oligonucleotides were synthesized, it can be concluded that methylation of the penultimate nucleotide can precede capping and methylation of the capping nucleotide. Our results also indicate that capping and methylation are processes that can take place prior to mRNA chain completion.
A proton gradient controls a calcium-release channel in sarcoplasmic reticulum.
Authors: Shoshan V , MacLennan D H , Wood D S
Published: May 2006

Sarcoplasmic reticulum vesicles from mammalian skeletal muscle have previously been shown to develop a proton gradient (alkaline inside) of 0.15-0.5 pH units during active Ca2+ uptake. We found that dissipation of this gradient by the proton ionophores gramicidin, nigericin, and carbonyl cyanide p-trichloromethoxyphenylhydrazone caused a rapid transient tension in skinned rabbit psoas muscle fibers. Increases, but not decreases, in medium pH of approximately 0.2 units over the range from pH 6.5 to pH 7.5 also elicited transient tensions. In isolated vesicles, physiological levels of Ca2+ (3.3 microM), inhibited pH-induced Ca2+ release. Dicyclohexylcarbodiimide blocked pH- and ionophore-induced Ca2+ release under conditions in which it could bind to sarcoplasmic reticulum proteins but did not inhibit Ca2+ uptake. We propose that a proton gradient generated across sarcoplasmic reticulum membranes during Ca2+ uptake maintains a Ca2+ release channel in a closed conformation and that dissipation of this gradient permits the Ca2+ release channel to open. We further propose that elevated myoplasmic Ca2+ also causes the Ca2+ channel to close, permitting Ca2+ uptake through Ca2+/Mg2+-ATPase to function effectively. As the proteolipids of sarcoplasmic reticulum bind dicyclohexylcarbodiimide under conditions in which Ca2+ release is blocked and as they have previously been shown to have Ca2+ ionophoric activity, we propose that the Ca2+-release channel either resides in the proteolipids or is controlled by H+ fluxes through the proteolipids.
Structural and motional changes in glyceraldehyde-3-phosphate dehydrogenase upon binding to the band-3 protein of the erythrocyte membrane examined with [15N,2H]maleimide spin label and electron paramagnetic resonance.
Authors: Beth A H , Balasubramanian K , Wilder R T , Venkataramu S D , Robinson B H , Dalton L R , Pearson D E , Park J H
Published: May 2006

Binding of the glycolytic enzyme, glyceraldehyde-3-phosphate dehydrogenase [GAPDHase; D-glyceraldehyde-3-phosphate:NAD+ oxidoreductase (phosphorylating EC 1.2.1.12], to the cytoplasmic segment of band-3 protein in the erythrocyte (RBC) membrane has been examined by electron paramagnetic resonance (EPR) and saturation transfer EPR (ST-EPR) spectroscopies. GAPDHase, which was isolated from rabbit muscle and labeled with the resolution-enhancing deuterated N-(15N-1-oxyl-2,2,6,6-tetramethyl-4-piperidinyl)maleimide spin label ([15N,2H]MSL), showed the same binding specificity for the transmembrane band-3 protein of human erythrocyte membranes as reported for unlabeled GAPDHase from human RBC. Experimental EPR lineshapes from soluble and membrane-bound enzymes were analyzed by direct stimulation of spectra and indicated a structural alteration of the bound GAPDHase in the vicinity of the spin label, which was attached covalently to the active-site cysteine-149 residue. A rigorous theoretical analysis of the ST-EPR spectra of soluble and membrane-bound enzyme is presented and utilized in conjunction with model system analysis to demonstrate that the motion of membrane-bound GAPDHase could be characterized by an effective isotropic rotational correlation time of 20 microseconds. This indicated that the GAPDHase--band-4 complex exhibits motional freedom relative to the membrane-spanning segment of the band-3 protein or the RBC. The double substituted spin label [15N,2H]MSL affords gains in sensitivity and resolution that permit studies of membrane-bound enzymes at physiological levels and quantitative simulations of the EPR and ST-EPR lineshapes with reasonable computation times.
Immunocytochemical localization of albumin in the secretory apparatus of rat liver parenchymal cells.
Authors: Yokota S , Fahimi H D
Published: May 2006

The localization of albumin was investigated in rat liver, fixed by perfusion, with peroxidase-labeled monospecific antibodies against rat serum albumin purified by affinity chromatography. By light microscopy, albumin is present uniformly in all parenchymal cells with no difference in the intensity of reaction in the different parts of hepatic lobules. By electron microscopy, albumin is localized in the entire secretory apparatus including the rough and smooth endoplasmic reticulum, Golgi complex, and secretory vacuoles. In the rough endoplasmic reticulum, focal negative segments are interposed between positive regions. In the Golgi region, albumin is found both in stacked cisternae and at the trans aspect in the portion called GERL (Golgi-endoplasmic reticulum--lysosome). Whereas albumin and lipoprotein particles are separated in terminal dilatations of the endoplasmic reticulum and in the cisternae on the cis face of the Golgi apparatus, they are usually intermixed in vacuoles of the trans face. Similarly, most secretion vacuoles below the sinusoidal lining contain albumin and lipoprotein particles together, although a few are also found with only one secretory product. These observations suggest that, after synthesis in the rough endoplasmic reticulum, albumin is segregated into smooth transitional elements and transported to the Golgi region where it is packaged together with other secretory products such as lipoproteins. These secretion vacuoles move up the sinusoidal surface, where they are discharged. The possible involvement of GERL in the proteolytic cleavage of proalbumin to albumin is considered.
Evidence for a relationship between longevity of mammalian species and life spans of normal fibroblasts
in vitro
and erythrocytes
in vivo
Authors: Röhme Dan
Published: May 2006

The replicative life spans of mammalian fibroblasts
in vitro
were studied in a number of cell cultures representing eight species. Emphasis was placed on determining the population doubling level at which phase III (a period of decrease in the rate of proliferation) and chromosomal alterations occur. All the cell cultures studied went through a growth crisis, a period of apparent growth cessation lasting for at least 2 weeks. In most cultures, the crisis represented the end of their replicative capacities, but in some cultures cell proliferation was resumed after the crisis. A predominantly diploid chromosome constitution (more than 75%) was demonstrated prior to the growth crisis. In cultures in which cell proliferation was resumed after the crisis, a nondiploid constitution prevailed in all cases except the rat (with 90% or more diploid cells all the time). The growth crisis occurred at population doubling levels that were characteristic for the species and was shown to be related to the species' maximal life span by a strict power law, being proportional to the square root of the maximal life span. Based on data in the literature, the same relationship was also valid for the lifespans of circulating mammalian erythrocytes
in vivo
. These results may indicate the prevalence of a common functional basis regulating the life span of fibroblasts and erythrocytes and thus operating in replicative as well as postmitotic cells
in vitro
and
in vivo
.
DNA replication-mediated recombination of molecules of adenovirus 2 DNA.
Authors: Wolgemuth D J , Hsu M T
Published: May 2006

Molecules of adenovirus 2 DNA were isolated as nucleoprotein complexes late in infection of HeLa cells and examined by electron microscopy. Some were interpreted as representing intermediates in recombination events. The structures observed were consistent with predicted intermediates according to the model for genetic recombination proposed by Meselson and Radding [Meselson, M. S. & Radding, C. M. (1975) Proc. Natl. Acad. Sci. USA 72, 358-361] and constitute physical evidence from animal cells in support of this model.
Biogenesis of membrane-bound and secreted immunoglobulins: two primary translation products of the human delta chain, differentially N-glycosylated to four discrete forms in vivo and in vitro.
Authors: McCune J M , Fu S M , Kunkel H G , Blobel G
Published: May 2006

Structural differences between the heavy chain of membrane IgD (delta m) and the heavy chain of secreted IgD (delta s) were investigated by using a human lymphoblastoid cell line that expresses idiotypically identical IgM and IgD. In a wheat germ cell-free system, mRNA from this cell line was shown to encode two distinct delta chains that differed in molecular weight. When translated in vitro in the presence of dog pancreatic microsomal membranes or when synthesized in vivo, these two delta chains were processed to four discrete glycosylated forms, all of which shared idiotypic determinants, C region determinants, and light chain linkage. As shown by digestion with endo-beta-N-acetylglucosaminidase H, these four delta forms represent two delta polypeptide chains that are differentially N-glycosylated. Pulse-chase experiments demonstrated that, after endo-beta-N-acetylglucosaminidase H treatment, delta m has a higher molecular weight than delta s. After integration into dog pancreatic microsomal membranes in vitro, delta m was found not to have a large cytoplasmic domain exposed to proteolytic digestion. The finding that delta m and delta s differ in primary structure is analogous to previous work with the corresponding heavy chains of IgM (mu m and mu s) from the same cell line. Thus, this cell line produces four Ig heavy chains (mu m, mu s, delta m, and delta s), with the same idiotype. The observation of differential N-glycosylation, apparently unique for the delta class, is discussed.
High molecular weight peptide with corticotropin-releasing factor activity from porcine hypothalami.
Authors: Schally A V , Chang R C , Arimura A , Redding T W , Fishback J B , Vigh S
Published: May 2006

The presence of a corticotropin-releasing factor (CRF) behaving as a peptide with a molecular weight of about 5000 was established after purification of porcine hypothalamic extracts by gel filtration on Sephadex G-25 and then on Sephadex G-50. Purified CRF stimulated the release of corticotropin (ACTH) in three in vitro systems: isolated rat pituitary quarters, monolayer cultures of dispersed pituitary cells, and superfused pituitary cells on a column. A linear logarithmic dose-response relationship existed between 50 and 200 micrograms of CRF preparations per ml and the total amount of ACTH released by the superfused pituitary cells. The pituitary ACTH response to CRF in the pituitary quarters system was also approximately linearly related to the logarithm of the dose of CRF. CRF also stimulated in vivo release of ACTH in rats pretreated with chlorpromazine, morphine, and Nembutal. CRF activity was labile to digestion with trypsin and chymotrypsin and was partially destroyed by pepsin. The evidence indicates that CRF of porcine origin is a polypeptide of a higher molecular weight than previously assumed.
Baboon endogenous virus genome: molecular cloning and structural characterization of nondefective viral genomes from DNA of a baboon cell strain.
Authors: Cohen M , Rein A , Stephens R M , O'Connell C , Gilden R V , Shure M , Nicolson M O , McAllister R M , Davidson N
Published: May 2006

Several heterogeneities in the baboon endogenous virus (BaEV) genomes that are present in the DNA of normal baboon tissues and the baboon cell strain BEF-3 have been described previously. To study these genomes, we cloned BaEV proviruses from BEF-3 cellular DNA into the lambda vector Charon 4A. Of the four full-length clones isolated, one was nondefective as determined by transfection. The sequence of a portion of this clone was found to code for amino acids 61-91 in the p30 region of the gag gene. This identification allowed us to align the restriction map with the BaEV genetic map. One heterogeneity, a BamHI site 2.4 kilobases (kb) from the proviral 5' end, was located close to the gag-pol junction; another, a BamHI site 1.4 kb from the 5' end of the genome, corresponded to the gag p30 coding sequence for amino acids 32-34; and a third, a Xho I site, was near the 3' end of the pol gene. To select the nondefective BaEV genomes from BEF-3 cells, we infected permissive cells with virus produced by BEF-3 cells and also transfected BEF-3 cellular DNA into permissive cells. The BaEV genomes in the permissive recipient cultures were then analyzed by restriction enzyme analysis. These nondefective genomes were found to be heterogeneous with respect to the gag-pol BamHI site and the Xho I site, but all were found to contain the BamHI site 1.4 kb from the 5' end of the genome.
Molecular engineering: An approach to the development of general capabilities for molecular manipulation
Authors: Drexler K. Eric
Published: May 2006

Development of the ability to design protein molecules will open a path to the fabrication of devices to complex atomic specifications, thus sidestepping obstacles facing conventional microtechnology. This path will involve construction of molecular machinery able to position reactive groups to atomic precision. It could lead to great advances in computational devices and in the ability to manipulate biological materials. The existence of this path has implications for the present.
Three tRNA binding sites on Escherichia coli ribosomes.
Authors: Rheinberger H J , Sternbach H , Nierhaus K H
Published: May 2006

The binding of N-acetyl-Phe-tRNAPhe (an analogue of peptidyl-tRNA), Phe-tRNAPhe, and deacylated tRNAPhe to poly(U)-programmed tightly coupled 70S ribosomes was studied. The N-acetyl-Phe-tRNAPhe binding is governed by an exclusion principle: not more than one N-acetyl-Phe-tRNAPhe can be bound per ribosome, although this peptidyl-tRNA analogue can be present either at the aminoacyl-tRNA (A) site or the peptidyl-tRNA (P) site. Two Phe-tRNAPhe molecules are accepted by one ribosome in the presence of poly(U). This aminoacyl-tRNA binds enzymatically (in the presence of elongation factor Tu and GTP) and nonenzymatically to the A site and is then transferred to the P site, if that site is free. If this elongation factor G-independent movement is hampered, either by using an incubation temperature of 0 degrees C or by the addition of the translocation inhibitor viomycin, only one Phe-tRNAPhe per ribosome can be bound. The effect of the peptidyltransferase inhibitor chloramphenicol on the binding is similar to that of viomycin. In the absence of poly(U), Phe-tRNAPhe cannot bind to the ribosome. Deacylated [14C]tRNAPhe can bind in three copies to one ribosome. The new third tRNA binding site is called the "E" site. The sequence of filling the sites is P, E, and A. The apparent binding constants for the P and the E sites are both approximately 9 X 10(6) M-1 and that for the A site is 1.3 X 10(6) M-1. In the absence of poly(U), only one deacylated tRNAPhe can be bound per ribosome. This tRNAPhe most likely occupies the P site.
Localization and nucleotide sequence of the gene coding for the woodchuck hepatitis virus surface antigen: comparison with the gene coding for the human hepatitis B virus surface antigen.
Authors: Galibert F , Chen T N , Mandart E
Published: May 2006

Nucleotide sequence analysis was performed with the Maxam--Gilbert method on a cloned woodchuck hepatitis virus DNA (Eco WHV DNA). The structural gene coding for the envelope protein of the virus was localized on the viral genome in the partially single-stranded region between map positions 91.2 and 71. This gene is composed of 669 nucleotides and can code for a polypeptide of 25,645 daltons. The DNA sequence and the deduced amino acid sequence were compared with those of the corresponding gene and surface antigen of the related hepatitis B virus, allowing some insight into the localization of the antigenic site.