bluuebunny/crossref_metadata_2025 huggingface dataset:
A sciatic nerve protein has a trophic effect on development and maintenance of skeletal muscle cells in culture.
Authors: Markelonis G , Tae Hwan O H
Published: May 2006

Citrate-soluble extracts of chicken sciatic nerve were fractionated biochemically and added to cultures of embryonic chicken skeletal muscle in order to identify the component that exerted trophic influences on the muscle. A protein fraction that expressed trophic activity was obtained by ion-exchange chromatography on DEAE-cellulose followed by gel filtration on Sephadex G-100 superfine. This fraction enhanced the rate and degree of morphological maturation and the level of protein synthesis in embryonic muscle cells. Muscle fibers treated with this fraction after maturation in culture survived for longer periods in vitro than did comparable controls. Characterization of the active protein fraction by sodium dodecyl sulfate/polyacrylamide gel electrophoresis revealed the presence of one major protein (molecular weight 84,000) and three minor proteins. Electrophoretic analysis of biologically inactive gel filtration fractions indicated that the three minor proteins were contaminants and that biological activity was associated with the protein of molecular weight 84,000. Analytical isoelectric focusing revealed that the active protein was acidic and focused as four species with isoelectric points (pI) of 5.74, 5.77, 5.92, and 6.15. Maximal incorporation of [14C]-leucine into muscle cell protein was elicited by 20 microgram of active protein per culture dish. These data suggest that an acidic protein having trophic influences upon muscle has been identified and partially purified.
Local density functional theory of atoms and molecules
Authors: Parr Robert G. , Gadre Shridhar R. , Bartolotti Libero J.
Published: May 2006

A local density functional theory of the ground electronic states of atoms and molecules is generated from three assumptions: (
i
) The energy functional is local. (
ii
) The chemical potential of a neutral atom is zero. (
iii
) The energy of a neutral atom of atomic number
Z
is -0.6127
Z
7/3
. The energy functional is shown to have the form [Formula: see text] where
A
0
=6.4563 and
B
0
=1.0058. The first term represents the electronic kinetic energy, the second term represents the electron—electron repulsion energy for
N
electrons, and the third term is the nucleus—electron attraction energy. The energy
E
and the electron density ρ are obtained and discussed in detail for atoms; their general properties are described for molecules. For any system the density becomes zero continuously at a finite distance from nuclei, and contours of the density are contours of the bare-nuclear potential
v
. For an atomic species of fractional charge
q
= 1 - (
N/Z
), an energy formula is obtained, [Formula: see text] which fits Hartree—Fock energies of 625 atoms and ions with root-mean-square error of 0.0270. A more general local density functional involving a coefficient
B(N)
=
B
0
N
2/3
+
B
1
is briefly considered.
Multiple discrete sites for premature RNA chain termination late in adenovirus-2 infection: enhancement by 5,6-dichloro-1-beta-D-ribofuranosylbenzimidazole.
Authors: Fraser N W , Sehgal P B , Darnell J E
Published: May 2006

Discrete-sized short RNA chains that contain the distinctive oligonucleotides, including the 5'-capped oligonucleotide, characteristic of the first 600 nucleotides of the adenovirus type 2 (Ad-2) large, late, rightward-reading transcriptional unit (16.4-99) accumulate in Ad-2-infected HeLa cells. In the presence of 5,6-dichloro-1-beta-D-ribofuranosylbenzimidazole the accumulation of these chains is enhanced, as is the accumulation of short chains from a neighbouring rightward-reading transcriptional unit (3.0-10.7). These short chains appear to represent prematurely terminated transcripts. Late in infection there is a marked increase in RNA synthesis, including that of prematurely terminated short chains, from the large late transcriptional unit. This suggests that the increase in transcription and mRNA production from this region late in infection is not due to reduced "attenuation" of RNA synthesis.
Poliovirus replicase: a soluble enzyme able to initiate copying of poliovirus RNA.
Authors: Dasgupta A , Baron M H , Baltimore D
Published: May 2006

The soluble phase of the cytoplasm of poliovirus-infected cells contains an enzymatic activity able to copy RNA without an added primer. This replicase activity has been purified 60-fold; it is absent from uninfected cells. Poly(U) polymerase activity copurifies with replicase activity. Although less pure replicase fractions copy a variety of RNAs, purer fractions respond better to poliovirus RNA than to other viral RNAs. Even the less pure fractions make a specific copy of the added template, as shown by hybridization of the product to its template RNA but not to other RNAs. Among homopolymers only poly(A)-oligo(U) was copied by the replicase; other primed homopolymer templates were inactive.
Intracellular localization of 125I-labeled insulin in hepatocytes from intact rat liver.
Authors: Carpentier J L , Gorden P , Barazzone P , Freychet P , Le Cam A , Orci L
Published: May 2006

We have shown that 125I-labeled insulin initially localizes to the plasma membrane of isolated rat hepatocytes. The ligand is subsequently internalized and preferentially localizes to lysosomal structures. Further, we have observed that labeled insulin localizes to regions of the cell rich in lysosomal and Golgi elements. In the present study in intact rat liver we found that, approximately 10 min after a pulse injection of 125I-labeled insulin, 56% of the label was internalized by the cell. When all grains are considered there is a preferential localization of grains to the biliary pole of the cell and these grains are almost all internalized and preferentially associated with lysosomes. These data, therefore, demonstrate that the lysosome-Golgi-rich area of the isolated hepatocyte corresponds to the biliary pole of the cell and there is a movement of the labeled hormone from its initial binding site on the plasma face of the cell membrane toward the biliary pole of the cell.
Vp1 affects intracellular localization of Vp3 polypeptide during simian virus 40 infection.
Authors: Kasamatsu H , Nehorayan A
Published: May 2006

In order to understand the functions of simian virus 40 genes, permissive cells (TC7) were infected with mutants temperature sensitive in the complementation groups A, B, C, BC, and D at permissive and nonpermissive temperatures. Cells were examined for the localization of viral polypeptide antigens by immunofluorescent staining with monospecific antibodies. The results are as follows: (i) The appearance of Vp1 antigen in cells infected by tsB, C, or BC mutants was not affected appreciably by the mutations. (ii) The appearance of Vp3 antigen was affected by the mutations in B, C, or BC. Vp3 antigen is confined to the nuclei in cells infected by wild-type virus. With mutant virus infection, Vp3 antigen is found in the cytoplasm, perinuclear region, and nucleoli. (iii) The tsD mutants and the tsA mutants did not express either Vp1 or Vp3 antigens at the nonpermissive temperature. (iv) Nucleoli seem to play an essential role in the biosynthesis and assembly of viral polypeptides. Thus, mutations in any one of complementation groups B, C, or BC, which are within the structural gene for Vp1, cause an alteration of intracellular distribution of another late gene product, Vp3. These results suggest that the amino acid sequences of Vp1 polypeptide play a role(s) in the transport of viral antigens across internal membranes or in virus assembly processes or in both.
Induction by lithium ion of multiplication of mouse mammary epithelium in culture.
Authors: Hori C , Oka T
Published: May 2006

Lithium ion at concentrations between 2 and 20 mM simulated the stimulatory effects of insulin on the uptake of alpha-aminoisobutyric acid, synthesis of RNA and DNA, and cell multiplication in mouse mammary gland explants cultured in a chemically defined synthetic medium. Other monovalent cations were virtually ineffective. In most instances the stimulatory effect of lithium ion was somewhat smaller than and additive to that of insulin. However, lithium ion was incapable of substituting for the action of insulin in augmenting milk protein synthesis in mammary explants cultured with other lactogenic hormones, prolactin, and glucocorticoid. The observed similarities of the responses of mammary cells to lithium and insulin suggest that possible importance of cation(s) in the regulation of mammary cell proliferation, which may be a common basis for the action of the two agents. On the other hand, the observed inability of lithium to mimic the lactogenic effect of insulin indicates a specific function of the hormone in the functional differentiation of mammary cells.
Hemoglobin ontogeny during normal mouse fetal development.
Authors: Brotherton T W , Chui D H , Gauldie J , Patterson M
Published: May 2006

Pure populations of large, nucleated erythrocytes derived from yolk sac blood islands were obtained during normal fetal mouse development. Embryonic hemoglobins were present in these cells early in gestation. Later in gestation, an increasing amount of adults hemoglobin was also synthesized and accumulated in this population of primitive nucleated erythrocytes, as demonstrated by both biochemical and immunocytochemical techniques.
Fixation of a deleterious allele at one of two "duplicate" loci by mutation pressure and random drift.
Authors: Kimura M , King J L
Published: May 2006

We consider a diploid population and assume two gene loci with two alleles each, A and a at one locus and B and b at the second locus. Mutation from wild-type alleles A and B to deleterious alleles a and b occurs with mutation rates va and vb, respectively. We assume that alleles are completely recessive and that only the double recessive genotype aabb shows a deleterious effect with relative fitness 1-epsilon. Then, it can be shown that if va greater than vb mutant a becomes fixed in the population by mutation pressure and a mutation-selection balance is ultimately attained with respect to the B/b locus alone. The main aim of this paper is to investigate the situation in which va = vb exactly. In this case a neutral equilibrium is attained and either locus can drift to fixation for the mutant allele. Diffusion models are developed to treat the stochastic process involved whereby the deleterious mutant eventually becomes fixed in one of the two duplicated loci by random sampling drift in finite populations. In particular, the equation for the average time until fixation of mutant a or b is derived, and this is solved numerically for some combinations of parameters 4Nev and 4Ne epsilon, where v is the mutation rate (va = vb = v) and Ne is the effective size of the population. Monte Carlo experiments have been performed (using a device termed "pseudo sampling variable") to supplement the numerical analysis.
Disparity of gene conversion in frameshift mutants located in locus
b2
of
Ascobolus immersus
Authors: Rossignol Jean-Luc , Paquette Normand
Published: May 2006

The frequency of conversion and the disparity in the direction of conversion were studied for six frameshift mutants lying in locus
b2
of
Ascobolus immersus
and giving more 2 wild type:6 mutant (2+6m) than 6 wild type:2 mutant (6+2m) aberrant asci (type B). The frequency of conversion decreased from left to right in the locus. The disparity steadily increased from left to right and then reached a plateau. Twenty-two frameshift mutants giving more 6+2m than 2+6m aberrant asci (type A) and closely linked to three type B mutants were also studied; they showed the same frequency of conversion and the same disparity (but in the opposite direction) as the type B mutant to which they are linked. The polar variation of both the frequency of conversion and the disparity as a function of position were expected on the basis of a previous study of 15 mutants giving postmeiotic segregations and located in locus
b2
. This variation is assumed to reflect the existence of a preferential region for the initiation of hybrid DNA (HDNA) during recombination and a duality in the distribution of this HDNA, with preponderant asymmetrical HDNA near the starting point and preponderant symmetrical HDNA farther from it.
Murine cytomegalovirus infects spermatogenic cells.
Authors: Dutko F J , Oldstone M B
Published: May 2006

Murine cytomegalovirus replicated in reproductive tissue of male mice infected with the virus. We examined three strains of mice latently infected by injection at birth with 100 plaque-forming units of the virus. As adults, these mice contained within their testes 4--6 viral genomic equivalents per 100 cells, as tested by hybridization between mouse DNA and cytomegalovirus DNA. Acutely infected male adult CBA mice homozygous for the nude gene (athymic: nude/nude) produced infectious virus in their testes, the amounts of which varied according to the animal's age at the time of infection. Heterozygous (nude/+) litter mates contained significantly less virus than nude/nude mice. At the peak of virus replication hybridization between virus DNA and mouse DNA indicated the presence of 3.3 viral genome equivalents per testicular cell. Both in situ hybridization studies and phenol emulsion reassociation of virus DNA to DNA from purified spermatozoa localized this viral DNA to immature and mature sperm cells. Hence, murine cytomegalovirus can be harbored in testes during both acute and latent infections and can replicate in male germ-line cells.
Amino-terminal sequence of bovine leukemia virus major internal protein: homology with mammalian type C virus p30 structural proteins.
Authors: Oroszlan S , Copeland T D , Henderson L E , Stephenson J R , Gilden R V
Published: May 2006

The amino acid composition, the COOH-terminal amino acid, and the NH2-terminal amino acid sequence of the first 55 residues of the major internal structural protein, p24, of bovine leukemia virus (BLV) were determined. The compositional data and the results of end-group analysis revealed that, although BLV p24 is chemically distinct, it more closely resembles the p30 structural proteins than the other gag gene products of mammalian retroviruses. It was found that BLV p24 shares the common NH2-terminal proline and COOH-terminal leucine but lacks the common prolylleucylarginine tripeptide and the larger conserved region found near the NH2 terminus of all mammalian type C viral p30s. Alignment of the amino acid sequence of BLV p24 with the previously determined sequence of feline leukemia virus p27 revealed a statistically significant sequence homology. A more distant relationship was found between BLV p24 and other mammalian p30s. The finding of a definite sequence homology between BLV p24 and mammalian type C virus p30s clearly establishes the origin of these contemporary viral proteins from common progenitor genes.
Evidence for internalization of the recognition site of β-adrenergic receptors during receptor subsensitivity induced by (-)-isoproterenol
Authors: Chuang De-Maw , Costa E.
Published: May 2006

In the supernatant (30,000 ×
g
) of frog erythrocyte homogenates, by using gel filtration we detected a protein that could bind [
3
H]dihydroalprenolol ([
3
H]DHA) with high affinity. This binding was greatly enhanced when the erythrocytes were preincubated with (-)-isoproterenol. After various periods of incubation with (-)-isoproterenol, the extent of the increase in the density of [
3
H]DHA binding sites in the cytosol was paralleled by a proportional decrease in the number of [
3
H]DHA binding sites in the corresponding pellet; both events peaked after 2-3 hr of incubation with (-)-isoproterenol. The
K
a
of the (-)-isoproterenol-induced increase in [
3
H]DHA binding in cytosol and the decrease in this binding in the membrane ranged between 60 and 90 nM. The changes in the cytosol and particulate [
3
H]DHA binding sites were independent of RNA and protein synthesis. The increase in cytosol binding elicited by (-)-isoproterenol was blocked by exposure of the cells to (-)-alprenolol which
per se
failed to change the cytosol binding of [
3
H]DHA. Scatchard analysis revealed that the enhanced [
3
H]DHA binding to cytosol material was due to a 4-fold increase in the
B
max
with little or no change in
K
d
(≈9 nM). Binding displacement data show that these soluble [
3
H]DHA binding sites resemble the surface membrane recognition sites. Moreover, the ability of various β-adrenergic agents to increase [
3
H]DHA binding to cytosol after they were incubated with frog erythrocytes paralleled their affinity for membrane-bound β receptors. These findings support the view that the β-adrenergic receptor desensitization caused by prolonged exposure to (-)-isoproterenol is due, at least in part, to an internalization of the recognition site of β-adrenergic receptors.
Middle ear muscles of the frog.
Authors: Wever E G
Published: May 2006

The anuran middle ear in its complete form includes two skeletal elements, the columella and operculum, each occupying a portion of the oval window of the otic capsule and each provided with a middle ear muscle. The two elements have an interlocking arrangement of a form that makes it possible for these muscles to exercise a high degree of control of sound transmission from tympanic membrane to inner ear receptors. From the anatomical relations it is inferred that the two muscles operate as antagonists so that contraction of the opercular muscle and relaxation of the columellar muscle leave the columella free to move in and out of the oval window in response to sound vibrations, whereas a contraction of the columellar muscle and relaxation of the opercular muscle tend to immobilize the columella and reduce the transmission inward. The frog thus achieves a degree of control of sound reception that probably is unmatched among vertebrate ears. The purpose of the middle ear mechanism is no doubt the protection of the inner ear receptors (the amphibian and basilar papillae) from overstimulation by sounds, including the animal's own cries and the intense clamor produced by a group of frogs calling in chorus.
Affinity labeling of the catalytic subunit of cyclic AMP-dependent protein kinase by N alpha-tosyl-L-lysine chloromethyl ketone.
Authors: Kupfer A , Gani V , Jiménez J S , Shaltiel S
Published: May 2006

The catalytic subunit of cyclic AMP-dependent protein kinase (from rabbit skeletal muscle; ATP:protein phosphotransferase, EC 2.7.1.37) was found to be irreversibly inactivated by chloromethyl ketone derivatives of lysine and phenylalanine, chemical reagents originally designed for labeling the active sites of the proteolytic enzymes trypsin and chymotrypsin. This inactivation was shown to occur at pH 7.5 and 22 degrees C, conditions under which chemically related alkylating reagents such as chloroacetamide and chloroacetic acid (which do not possess the amino acid side chain) fail to inactivate the enzyme. In the case of the chloromethyl ketone derivative of N alpha-tosyl-L-lysine, the enzyme could be protected by its nucleotide substrate (MgATP), by one of its protein substrates (histone H2b), and by its regulatory subunit which, upon binding, shields the active site of the catalytic subunit. Differential labeling experiments, together with kinetic studies of the rates of modification of the sulfhydryl groups in the enzyme before and after inactivation with the chloromethyl ketone, suggest that the loss of activity is associated with one (kinetically characterized) sulfhydryl group present either at the active site of the enzyme or at a site intimately associated with it. The general implications of these results regarding the interpretation of affinity labeling experiments carried out in complex mixtures of proteins or under in vivo conditions are discussed.
Sequence relationships among defective interfering influenza viral RNAs.
Authors: Davis A R , Nayak D P
Published: May 2006

Each clone of ts-52 and ts+ WSN influenza virus, when serially passaged at high multiplicity, gives rise to defective interfering (DI) virus with a unique set of new RNA species. The new RNAs (DI RNA) from several DI viruses were examined by the technique of RNase T1 oligonucleotide two-dimensional electrophoresis. It was found that each DI RNA arises from a specific segment of standard viral RNA. All DI RNA studied arose from the viral polymerase genes (P1, P2, and P3). DI RNAs originating from the same polymerase gene were interrelated. Certain of these DI RNAs appeared to contain completely overlapping nucleotide sequences. Others contained both overlapping and nonoverlapping nucleotide sequences. The latter DI RNAs may be formed from the progenitor viral RNA segment by a mechanism other than a common initiation (or termination) point and a simple deletion from one end.
Isolation and mapping of plasmids containing the Salmonella typhimurium origin of DNA replication.
Authors: Zyskind J W , Deen L T , Smith D W
Published: May 2006

A purified EcoRI restriction endonuclease fragment that determines resistance to kanamycin and is incapable of self-replication was used to select autonomously replicating fragments from an EcoRI digest of a Salmonella typhimurium F' plasmid containing the chromosomal region believed to include the S. typhimurium origin of DNA replication. Both the F factor and S. typhimurium chromosome replication origins were cloned by this procedure. The EcoRI fragmentment containing the S. typhimurium origin of replication is 19.4 kilobase pairs long and includes functional asp+ and uncB+ genes. Restriction endonuclease analysis of deletions obtained from the S. typhimurium origin plasmid indicated that the replication origin (ori region) is contained within a 3.3-kilobase pair region. Comparison with Escherichia coli origin plasmids shows colinearity of gene arrangement on the chromosomes in this region and suggests that some, but not all, regions of the nucleotide sequence in the origin region may be conserved (identical) in these two bacterial species.
In vitro core particle and nucleosome assembly at physiological ionic strength.
Authors: Ruiz-Carrillo A , Jorcano J L , Eder G , Lurz R
Published: May 2006

Nucleosome core particles have been efficiently assembled in vitro by direct interaction of histones and DNA at physiological ionic strength, as assayed by digestion with DNases, supercoiling of relaxed circular DNA, and electron microscopy. Reconstitution was achieved either by the simultaneous addition of all core histones, or by the sequential binding of H3 . H4 tetramer and H2A . H2B dimer to DNA. Micrococcal nuclease digestion and electron microscopy studies indicated that there is heterogeneity in the spacings at which core particles are assembly on the DNA. Length measurements of oligomeric DNA produced during the course of the digestion suggest that the core histone octamer can organize 167 (+/- 4) rather than 145 base pairs of DNA, the extra 20 base pairs being quickly digested. Binding of histone H1 to core particles resulted in the protection of about 165 base pairs of DNA from nuclease attack. Because the core histone octamer is fully dissociated into H3 . H4 tetramer and H2A . H2B dimer at physiological ionic strength, our results would suggest that in vivo core particle assembly may also occur by interaction of these two complexes on the nascent DNA.
Increase of normal myeloblast viability and multiplication without blocking differentiation by type C RNA virus from myeloid leukemic cells.
Authors: Liebermann D , Sachs L
Published: May 2006

Clones of mouse myeloid leukemic cells that differ in their competence to be induced for normal cell differentiation by the protein inducer MGI produce type C virus. These viruses have been studied for their effect on the viability, multiplication, and differentiation of normal bone marrow cells either with or without the addition of MGI. Virus from leukemic clones that can differentiate normally to mature macrophages and granulocytes (MGI+D+ clones) induced some multiplication of myeloblasts in the bone marrow, but the cells did not differentiate without adding MGI. In the presence of MGI, this virus then induced an increased number of colonies whose cells differentiated to mature macrophages or granulocytes as in colonies of uninfected cells. Virus infection also resulted in a decrease in the amount of MGI and fetal calf serum that was required for colony formation. Virus from MGI+D+ clones, in the presence of MGI, was 500-fold more effective in increasing colony formation than virus from the differentiation-defective MGI-D- clones, although both types of virus replicated with equal efficiency in the normal bone marrow cells. No such increase was obtained after infection with the Friend leukemic virus complex or the Moloney murine leukemia virus. Infection with virus from a MGI+D+ clone that was differentiated by MGI mainly to macrophages induced a higher percentage of macrophage colonies than virus from MGI+D+ clones that were differentiated by MGI to granulocytes and macrophages. Studies with isolated myeloblast colony-forming cells from the bone marrow have indicated that these are the target cells for the virus. Infections of these isolated myeloblasts with virus from MGI+D+ clones induced some multiplication without differentiation in the absence of MGI, and increased the viability and multiplication of the myeloblasts without inhibiting their ability to differentiate in the presence of MGI. The results, therefore, indicate that virus from MGI+D+ cells can increase the viability and multiplication of normal myeloblasts in the bone marrow without blocking the ability of these cells to be induced to differentiate by MGI, and that this effect was directly related to the competence of the leukemic host cells to be induced for normal differentiation. It is suggested that the difference between the effect of virus from MGI+D+ and MGI-D- cells may be due to a difference in their integration sites in relation to the genes that control cell viability, multiplication, and differentiation.
Assembly and secretion of pentameric IgM in a fusion between a nonsecreting B cell lymphoma and an IgG-secreting plasmacytoma.
Authors: Raschke W C , Mather E L , Koshland M E
Published: May 2006

A new immunoglobulin product has been obtained by hybridization of mouse cell lines arrested at different stages in B lymphocyte development. One line was shown to have the characteristics of an undifferentiated B cell that synthesizes monomeric IgM as a membrane receptor but does not express J chain. The second line was represent of a fully differentiated plasma cell synthesizing large amounts of IgG and J chain, but no IgM. Fusion of the two cell types yielded independent hybrid clones that secreted pentameric IgM, normally the first product of antigen-driven B cell differentiation. Analyses of the hybrid cells indicated that the IgM was expressed as a result of complementation between the synthetic capacities of the parental lines. The hybrid cells synthesized both monomeric IgM and J chain and assembled these components into a pentameric molecule with the expected stoichiometry of one J chain per five monomeric units. These findings provided further evidence that the induction of B cell differentiation includes a signal for de novo synthesis of the J chain. Moreover, the complementation achieved by this hybridization provides a system for identifying other intracellular events in B cell differentiation to IgM secretion.
Distribution of 5'-nucleotidase in human lymphoid tissues.
Authors: Edwards N L , Gelfand E W , Burk L , Dosch H M , Fox I H
Published: May 2006

Low activity of 5'-nucleotidase (5'-ribonucleotide phosphohydrolase, EC 3.1.3.5) in T lymphoblasts may explain the marked sensitivity of this cell to deoxynucleotide accumulation when compared to B lymphoblasts. The relevance of such observations with cultured cells to the normal immune system requires the demonstration of similar differences in the 5'-nucleotidase activity of normal human lymphocyte subpopulations. Sheep erythrocyte (E) rosette-forming cells from normal thymus, tonsil, and peripheral mononuclear cells have 5'-nucleotidase activities of 1.7, 11.3, and 21.2 nmol/hr per 10(6) cells. Non-E-rosette forming cells from the peripheral blood or tonsil have 5'-nucleotidase activity comparable to the higher levels found in the peripheral E-RFC. Increased levels of 5'-nucleotidase activity may be a marker for post-thymic T lymphocytes. T lymphoblasts have 5'-nucleotidase activity similar to values demonstrated for E-RFC in thymus, whereas cultured B lymphoblasts have 5'-nucleotidase activity 15 times greater than that of T lymphoblasts. On the basis of these observations, the 5'-nucleotidase deficiency in congenital agammaglobulinemia has been reevaluated. In these patients the data indicate that peripheral E-rosette forming cells have the enzyme deficiency, demonstrating an abnormality of T lymphocytes in this disorder of immunoglobulin production.
Characterization of double-stranded ribonucleic acid in tobacco leaves
Authors: Ikegami M. , Fraenkel-Conrat H.
Published: May 2006

Double-stranded RNA was isolated from tobacco leaves and characterized in terms of base composition, density, and nuclease resistance. Although its role in the plant's physiology is not clear, evidence was adduced that it is the product of the RNA-dependent RNA polymerase previously shown to occur in this and other plants. The fact that twice as much fully than partially double-stranded RNA appears to be made favors a regulatory role for the double-stranded RNA rather than a transcriptional intermediate role.
Comparison of mRNA precursors in plasmacytomas producing closely related κ chains
Authors: Perry Robert P. , Kelley Dawn E. , Schibler Ueli
Published: May 2006

To help elucidate the mechanisms of formation and expression of active immunoglobulin genes, we have made a systematic study of the processing patterns of the mRNAs that code for a closely related family of κ chains. Among the members of this family, represented by the V
κ
21 group of plasmacytomas, are examples in which six different germ-line
V
genes are joined to four different J segments in various combinations. The mRNA precursors were identified by hybridizing a cloned κ-cDNA probe to poly(A)-containing nuclear RNAs that were size fractionated on methylmercury-agarose gels and transferred to diazotized paper. Based on the length of the segment excised in the last detectable processing step, which presumably represents the removal of the J-C intron, the precursor patterns were classified into four primary categories that correlated well with the type of J segment being expressed. The J segments were thus located at distances ranging from 2.4 to 4.8 kilobases from the constant-region gene. Different
V
genes joined to the same J segment exhibited similar precursor patterns, suggesting that the size of the translocated V segment may be relatively uniform among members of the V
κ
21 group. A large (9.1 kilobases) component, which is likely to represent a primary transcription product, was observed in all processing categories, regardless of which J segment was being utilized. This surprising observation leads to some interesting predictions about the mechanism of V-J translocation.
Titin: major myofibrillar components of striated muscle.
Authors: Wang K , McClure J , Tu A
Published: May 2006

Electrophoretic analyses of protein components of striated muscle myofibril purified from various vertebrate and invertebrate species revealed that proteins much larger than myosin heavy chain are present in significant amounts. To define possible roles of these heretofore unidentified proteins, we purified a combination of two uncommonly large proteins, designated as titin, from chicken breast myofibrils. Chemical and immunological studies indicated that titin is distinct from myosin, actin, and filamin. Specific titin anti body crossreacts with similar protein in both skeletal and cardiac myofibrils of many vertebrate and invertebrate species. Immunofluorescent staining of glycerinated chicken breast myofibrils indicated that titin is present in M lines, Z lines, the junctions of A and I bands, and perhaps throughout the entire A bands. Similar staining studies of myofibrils from other species suggest that titinlike proteins may be organized in all myofibrils according to a common architectural plan. We conclude that titin is a structurally conserved myofibrillar component of vertebrate and invertebrate striated muscles.
Production and characterization of a monoclonal antibody to chicken type I collagen.
Authors: Linsenmayer T F , Hendrix M J , Little C D
Published: May 2006

We have shown that lymphocyte-myeloma cell hybridization can be used to produce large amounts of extremely high-titer specific antibodies against type I collagen, a macromolecule normally of low immunogenicity. In a passive hemagglutination assay the antibody had a high titer against chicken type I collagen but showed no activity against chicken type II or rat type I collagen. By using a two-step fluorescence histochemical procedure on sections of embryonic chicken tibia, strong fluorescence was observed in the perichondrium and surrounding connective tissue (known to contain type I collagen) but not over the cartilage (characterized by type II collagen). When used in conjunction with Staphylococcus aureus as a solid phase immunoadsorbant, the antibody was shown to bind to labeled collagen synthesized in vitro by embryonic chicken calvaria.
Reverse transcriptase pauses at N2-methylguanine during in vitro transcription of Escherichia coli 16S ribosomal RNA.
Authors: Youvan D C , Hearst J E
Published: May 2006

A restriction fragment strand complementary to a sequence near the 3' end of Escherichia coli 16S rRNA has been used to prime reverse transcriptase (avian myeloblastosis virus RNA-directed DNA nucleotidyltransferase; deoxynucleosidetriphosphate:DNA deoxynucleotidyltransferase, EC 2.7.7.7). In addition to transcripts that were extended to the 5' end of the RNA, two major transcription intermediates were observed. These discrete-sized cDNA intermediates are the result of a kinetic barrier imposed by monomethylation of the amino group on guanine that participates in base-pairing. Both major transcription intermediates correspond to attenuation at the known positions of N2-methylguanine (m2G) in the rRNA sequence. The relaxation time for elongation of the cDNA through m2G is approximately 3 min. No other major kinetic pauses were observed in the 1340 bases transcribed.
Primary structure of the NH2-terminal extra piece of the precursor to human placental lactogen.
Authors: Sherwood L M , Burstein Y , Schechter I
Published: May 2006

The cell-free translation product of human placental lactogen mRNA is a precursor molecule larger than the mature hormone that circulates in plasma. To determine the structure of pre-placental lactogen, the poly(A)-rich RNA fraction of term placenta was isolated and translated in a wheat germ cell-free system. The mRNA programmed the synthesis of a major protein, 3000 daltons larger than placental lactogen, that was specifically precipitated by hormone antibodies. The immunoprecipitated protein was labeled separately with 20 radioactive amino acids and subjected to sequence analysis. The results showed the synthesis of pre-placental lactogen in which an extra piece 25 residues long preceded the NH2 terminus of the mature protein. The structure of the extra piece is as follows: Met-Pro-Gly-Ser-Arg-Thr-Ser-Leu-Leu-Ala-Phe-Ala-Leu-Leu-Cys-Leu-Pro-Trp-Leu-Gln-Glu-Ala-Gly-Ala-. Met1 is the initiator residue because only initiator [35S]Met-tRNAMet1, but not internal [35S]Met-tRNA2Met, donated NH2-terminal methionine. The structure of the extra piece showed little homology with that of unrelated hormones but striking homology (64%) with the extra piece of rat pre-growth hormone. Most amino acid substitutions involved a single base change in the codon. Mature human placental lactogen and rat growth hormone have 59% homology in sequence. Thus, our findings provide additional evidence to support the common evolutionary origin of these hormones, not only of the mature proteins but also of the extra piece segments.
High-frequency transformation of yeast by plasmids containing the cloned yeast
ARG4
gene
Authors: Hsiao Chu-Lai , Carbon John
Published: May 2006

Hybrid ColE1 plasmids, containing cloned DNA from the yeast
ARG4
region [e.g., pYe(
arg4
)1], transform yeast
arg4
mutants to
ARG4
+
with a frequency of 10
-4
(about 10
3
transformants per μg of plasmid DNA) and can replicate autonomously without integrating into the yeast genome. The yeast transformants are genetically unstable when grown on nonselective medium, but can be readily grown and maintained on minimal medium lacking arginine. The existence of unintegrated replicating plasmid DNA in the yeast transformants was demonstrated by Southern gel hybridization and by transformation of
Escherichia coli argH
mutants with DNA preparations from yeast transformants and subsequent recovery of intact plasmid DNA from the bacterial transformants. Plasmid DNAs recovered from the
E. coli
-yeast-
E. coli
“shuttle” remain essentially unchanged, as judged by DNA restriction fragment patterns. Some plasmid mutations leading to increased efficiency of expression of the
ARG4
gene in
E. coli
do not appear to affect expression of the cloned
ARG4
gene in yeast. Appropriate derivatives of these
ARG4
plasmids are of potential usefulness as vectors for cloning genes in yeast and for studying the mechanism of yeast DNA replication.
Methylation of
Herpesvirus saimiri
DNA in lymphoid tumor cell lines
Authors: Desrosiers Ronald C. , Mulder Carel , Fleckenstein Bernhard
Published: May 2006

Several continuous lymphoid cell lines have been established from tumors induced by
Herpesvirus saimiri
. At least a portion of the viral DNA in the marmoset lymphoid cell line 1670, which does not produce detectable virus, is present as covalently closed circular episomal DNA. The use of restriction endonuclease digestion, transfer to nitrocellulose filters, and hybridization of the virus-specific DNA has produced strong evidence that viral DNA sequences present in total 1670 cell DNA and in isolated episomes are extensively methylated. The restriction endonuclease
Hpa
II has the same recognition sequence as
Msp
I but, unlike
Msp
I, fails to cleave when the C of the C-G dinucleotide is methylated. Viral DNA sequences of 1670 cells are refractory to cleavage by
Hpa
II but not
Msp
I; greater than 80% of the
Hpa
II cleavage sites appear to be methylated. Similarly, viral DNA sequences of 1670 cells are refractory to cleavage by
Sma
I (C-C-C-G-G-G) and
Sac
II (C-C-G-C-G-G) but not
Sac
I,
Pvu
II, or
Pst
I, which lack the dinucleotide C-G in their recognition sequences. Methylation of mammalian DNA has been previously found exclusively at C residues in the dinucleotide C-G.
H. saimiri
DNA sequences of another nonproducer cell line, 70N2, also appeared to be extensively methylated, but analysis of total cell DNA extracted from three virus-producing lymphoid lines revealed no evidence of methylation of viral DNA sequences. It remains to be seen if methylation of viral DNA plays a role in the lack of complete expression of
H. saimiri
genome information in nonproducing lymphoid cell lines.
Torsional stress and local denaturation in supercoiled DNA.
Authors: Benham C J
Published: May 2006

It is shown that local denaturation can be a natural consequence of supercoiling, even in environments where base pairing of linear DNA is energetically favored. Any change in the molecular total twist from its unstressed value is partitioned between local denaturation and smooth twisting in both the native and coil regions so as to minimize the total conformational free energy involved. Threshold degrees of torsional deformation are found for the existence of stable, locally melted conformations. As these thresholds are surpassed, the number of denatured bases increase smoothly from zero. Existing experimental evidence regarding denaturation in supercoiled DNA is in good agreement with the predictions of this theory. In addition, from existing data one can estimate the partitioning of superhelicity between twisting and writhing. Possible consequences of stress-induced strand separation on the accessibility of the DNA to enzyme attack are discussed. Control of local melting by DNA topoisomerases and DNA gyrases could regulate diverse events involved in transcription, replication, recombination, and repair.
Antitubulin agents enhance the stimulation of DNA synthesis by polypeptide growth factors in 3T3 mouse fibroblasts.
Authors: Friedkin M , Legg A , Rozengurt E
Published: May 2006

Colchicine and other antitubulin agents markedly enhanced the stimulation of DNA synthesis by combinations of various growth factors such as epidermal growth factor, insulin, fibroblast-derived growth factor, and vasopressin in serum-free cultures of several quiescent 3T3 mouse fibroblast cell lines. Enhancing effects were observed based on continuous incorporation of [3H]thymidine into DNA as well as by autoradiographic labeling of cell nuclei. The concentration of colchicine and podophyllotoxin required to produce half-maximal enhancement of DNA synthesis stimulated by epidermal growth factor and insulin was 25-50 nM. Lumicolchicine did not produce enhancing effects. The disassembly of microtubules resulting from the action of colchicine, Colcemid, and vinblastine did not inhibit the stimulation of DNA synthesis in quiescent Swiss 3T3 fibroblasts by fetal bovine serum. We conclude that the cytoplasmic microtubule network in 3T3 mouse fibroblasts does not exert a positive regulatory function in the initiation of DNA synthesis but rather can produce a constraint on the initial action of the peptide growth factors in serum-free media.
Segregation of pre-stalk and pre-spore cells of Dictyostelium discoideum: observations consistent with selective cell cohesion.
Authors: Feinberg A P , Springer W R , Barondes S H
Published: May 2006

Aggregating Dictyostelium discoideum cells were dissociated and separated into two populations, pre-stalk and pre-spore cells, by centrifugation in a Percoll gradient. After harvesting, one population of cells was labeled with fluorescein isothiocyanate and the other with tetramethylrhodamine isothiocyanate. Equal numbers of the two cell populations were then mixed and observed while they aggregated and differentiated to form fruiting bodies. Within minutes after mixing, the two populations showed evidence of segregation and tended to form separate streams of cells as they migrated toward aggregation centers. Many separate clusters of tetramethylrhodamine isothiocyanate-labeled or fluorescein isothiocyanate-labeled cells were found within an aggregation center. Thereafter there was further segregation. The denser cells from the gradient tended to assume the position of stalk cells whereas the lighter cells migrated to the position characteristic of spore cells. The patterns of segregation suggest that selective cohesiveness of one or both cell types plays a role in morphogenesis.
Quantitation of phosphatidylcholine secretion in lung slices and primary cultures of rat lung cells
Authors: Keller George H. , Ladda Roger L.
Published: May 2006

Rat lung slices and isolated rat lung cells were used to study the secretion of phosphatidylcholine by the lung
in vitro
. The rate of incorporation of [
3
H]choline by lung slices was 20-fold greater than by liver slices and 4-fold greater in lung cells compared to confluent skin fibroblasts. Labeling lung slices or cells with [
3
H]choline for up to 8 hr failed to reveal a significant amount of labeled phosphatidylcholine in the medium of either system compared to the medium from liver slice or fibroblast controls. Labeling of isolated lung cells for up to 24 hr, with or without 10% fetal calf serum, also showed no significant difference in the amount of labeled phosphatidylcholine in the medium compared to control fibroblast cultures. Washing labeled lung slices or cells with a nonlysing concentration of Triton X-100 (0.05%) did not selectively release labeled phosphatidylcholine, indicating that any secreted phosphatidylcholine did not adhere to the surface of the lung slices or cells. Experiments were performed to determine whether the small amount of phosphatidylcholine in the medium and detergent-released phosphatidylcholine was similar to the tissue and cell phosphatidylcholine. The saturated fatty acid composition of the phosphatidylcholine released by Triton X-100 and in the medium (from lung slices) was identical to that of the tissue phosphatidylcholine. In addition, the relative labeling rates of the phospholipids released by Triton X-100 and in the medium (labeled with [
14
C]glycerol) were identical to those of the tissue and cell phospholipids. Based on these results, we conclude that phosphatidylcholine is not secreted by lung slices and lung cells in large amounts compared to controls. The implication of these data is that pulmonary surfactant material may actually not be secreted by the lung
in vitro
, and perhaps
in vivo
, in the manner that is currently generally accepted.
1H nuclear magnetic resonance investigation of flexibility in DNA.
Authors: Early T A , Kearns D R
Published: May 2006

In this paper we report successful observations of proton NMR spectra of native double helical salmon sperm and calf thymus DNA of various lengths. Measurements of the linewidths arising from proton--proton dipolar interactions are used to obtain information about the dynamic behavior of DNA helices in solution. Depending upon which protons are used to monitor the local internal motions of the DNA, different results are obtained. The lowfield resonances from hydrogen-bonded imino protons in the base pairs indicate that the correlation time for reorientation of base pairs is less than 3 x 10(-7) sec, whereas correlation times for motion of neighboring sugar protons relative to the aromatic protons are less than 5 x 10(-8) sec for DNA that is over 200 base pairs long. These observations indicate that there is considerably more internal flexibility in the DNA molecues, especially in the backbone, than is indicated by classic hydrodynamic studies of DNA.
Structural geology of the Earth's interior
Authors: Jordan Thomas H.
Published: May 2006

Seismology is providing a more sharply focused picture of the Earth's internal structure that should lead to improved models of mantle dynamics. Lateral variations in seismic wave speeds have been documented in all major layers of the Earth external to its core, with horizontal scale lengths ranging from 10 to 10
4
km. These variations can be described in terms of three types of heterogeneity: compositional, aeolotropic, and thermobaric. All three types are represented in the lithosphere, but the properties of the deeper inhomogeneities remain hypothetical. It is argued that sublithospheric continental root structures are likely to involve compositional as well as thermobaric heterogeneities. The high-velocity anomalies characteristic of subduction zones—seismic evidence for detached and sinking thermal boundary layers—in some areas appear to extend below the seismicity cutoff and into the lower mantle or mesosphere. Mass exchange between the upper and lower mantles is implied, but the magnitude of the flux relative to the total mass flux involved in plate circulations is as yet unknown. Other observations, such as the vertical travel time anomalies seen in the western Pacific, may yield additional constraints on the flow geometries, but further documentation is necessary. Thermobaric heterogeneities associated with a thermal boundary layer at the base of the mantle could provide the explanation for some of the observations of heterogeneities in the deep mantle. The evidence for very small scale inhomogeneities (<50 km) in region D″ and for topography on the core-mantle interface motivate the speculation that there is a chemical boundary layer at this interface, as well as a thermal one.