bluuebunny/crossref_metadata_2025 huggingface dataset:
Photorespiration mutants of
Arabidopsis thaliana
deficient in serine-glyoxylate aminotransferase activity
Authors: Somerville C. R. , Ogren W. L.
Published: May 2006

Three mutants of the crucifer
Arabidopsis thaliana
(Linnaeus) Heynhold were isolated that are completely lacking in activity catalyzed by serine-glyoxylate aminotransferase (EC 2.6.1.45), a peroxisomal enzyme involved in photorespiratory carbon metabolism. These mutants were viable and exhibited normal photosynthesis under conditions that suppressed photorespiration, but they were inviable and photosynthesized at greatly reduced rates under conditions that promoted photorespiration. Serine and glycine accumulated as end products of photosynthesis in the mutants, mostly at the expense of starch and sucrose. The mutants are allelic, and the segregation patterns of plant viability, photosynthetic activity, and enzyme activity in the F
1
and F
2
generations indicated that all the observed effects were caused by a single recessive nuclear mutation. This conclusion was confirmed by the isolation of seven revertants in which viability, photosynthetic capacity, and enzyme activity were simultaneously restored. Mutants of the type described here, in which photorespiration is changed from a merely wasteful process into one that is lethal, may permit the direct selection of secondary mutations that reduce photorespiration.
Isolation of a Chinese hamster fibroblast mutant defective in hexose transport and aerobic glycolysis: its use to dissect the malignant phenotype.
Authors: Pouysségur J , Franchi A , Salomon J C , Silvestre P
Published: May 2006

A procedure is described for the selection of glucose uptake mutants based upon radiation suicide of Chinese hamster fibroblasts by 2-deoxy[3H]glucose. In one of these mutants, DS 7, the ability to transport either 2-deoxyglucose or 3-O-methylglucose was decreased to one-fifth to one-fourth. Besides this defect, DS7 produces 1/14th the lactic acid produced by the parent when grown on 5 mM glucose. This block in aerobic glycolysis is due to a mutation that affects the expression of the phosphoglucose isomerase gene because no isomerase activity is detected in cell extracts of DS7. This glycolytic block makes that cell line dependent exclusively on respiration for its energy requirement. Consequently, DS7 survives well after removal of glucose but dies quickly in the presence of oligomycin. The parental line O23 (subclone of CCl39) grows at low serum concentration, is anchorage-independent, and is tumorigenic in nude mice. The derived glycolytic mutant DS7 has retained both the in vitro transformed phenotype (low serum dependence and loss of anchorage dependence) and the tumor-forming capability. The tumor cells derived from the injection of DS7 cells have kept the original glycolytic defect. This finding suggests that the transformed properties (high hexose transport and aerobic glycolysis) that can be uncoupled from abnormal growth control are not necessary for the expression of the malignant phenotype in fibroblasts.
Rare structural variants of human and murine uroporphyrinogen I synthase.
Authors: Meisler M H , Carter M L
Published: May 2006

An isoelectric focusing method for detection of structural variants of the enzyme uroporphyrinogen I synthase [porphobilinogen ammonia-lyase (polymerizing), EC 4.3.1.8] in mammalian tissues has been developed. Mouse and human erythrocytes contain one or two major isozymes of uroporphyrinogen I synthase, respectively. Other tissues contain a set of more acidic isozymes that are encoded by the same structural gene as the erythrocyte isozymes. Mouse populations studied with this method were monomorphic for uroporphyrinogen I synthase, with the exception of one feral mouse population. The pedigree of a human family with a rare structural variant is consistent with autosomal linkage of the structural gene. This system provides a convenient isozyme marker for genetic studies and will facilitate determination of the chromosomal location of the uroporphyrinogen I synthase locus.
Specific receptors for the serum thymic factor (FTS) in lymphoblastoid cultured cell lines.
Authors: Pléau J M , Fuentes V , Morgat J L , Bach J F
Published: May 2006

The interaction of the synthetic serum thymic factor (FTS, "facteur thymique sérique") with human T lymphocytes from two established T cell lines (1301 and HSB2) was studied by using [3H]FTS. At 30 degrees C, in the presence of 10 nM labeled FTS, a steady state was observed within 120 min. Bound labeled FTS was dissociated by simultaneous addition of an excess of unlabeled FTS (dissociation constant Kd = 3 nM). The binding of [3H]FTS was reduced to 10-20% when unlabeled FTS was added at 20 microgram/ml (20 micro M), but not when unrelated peptides or FTS analogues differing from FTS by only one amino acid residue were added. No FTS binding was detectable on B and null cell lines or on two T cell lines other than 1301 and HSB2. These data indicate that only certain T cell subsets possess receptors with high affinity and specificity for FTS.
One-sided difference schemes and transonic flow
Authors: Engquist Bjorn , Osher Stanley
Published: May 2006

Two one-sided conservation form difference approximations to a scalar one-dimensional convex conservation law are introduced. These are respectively of first- and second-order accuracy and each has the minimum possible band-width. They are nonlinearly stable, they converge only to solutions satisfying the entropy condition, and they have sharp monotone profiles. No such stable approximation of order higher than two is possible. Dimensional splitting algorithms are constructed and used to approximate the small-disturbance equation of transonic flow. These approximations are also nonlinearly stable and without nonphysical limit solutions.
Mechanism of thermal rearrangement of the spiro bicyclo[2.1.0]-pentane-5,2′-methylenecyclopropanes to 6- and 7- methylenebicyclo[3.2.0]hept-1-enes
Authors: Lokensgard David M. , Dougherty Dennis A. , Hilinski Edwin F. , Berson Jerome A.
Published: May 2006

The thermal rearrangements of the bicyclo[2.1.0]pentane-5,2′-methylenecyclopropanes fall into two classes. The first occurs near 80°C and consists of a double epimerization (“bridge flip”) which is initiated by cleavage of the bridge bond. An alternative mechanism by way of a trimethylenemethane intermediate is ruled out by an isotopic position-marking experiment. The second rearrangement begins to be detected above 120°C. It gives the isomeric 6- and 7-methylenebicyclo[3.2.0]hept-1-enes. Two possible mechanisms can operate in this complex change, but a choice between them is not yet possible.
Dielectric constant of atomic fluids with variable polarizability
Authors: Alder B. J. , Beers J. C. , Strauss H. L. , Weis J. J.
Published: May 2006

The Clausius-Mossotti function for the dielectric constant is expanded in terms of single atom and pair polarizabilities, leading to contributions that depend on both the trace and the anisotropy of the pair-polarizability tensor. The short-range contribution of the anisotropic part to the pair polarizabilities has previously been obtained empirically from light scattering experiments, whereas the trace contribution is now empirically determined by comparison to dielectric experiments. For helium, the short-range trace part agrees well with electronic structure calculations, whereas for argon qualitative agreement is achieved.
Internal supersymmetry and unification
Authors: Ne'eman Yuval , Sternberg Shlomo
Published: May 2006

We construct a family of finite-dimensional representations of the superalgebra
sl
(
n
/
m
) that depend on an integer parameter for
m
> 1 and on a complex parameter,
b
, for
m
= 1. We describe some models of elementary particles for
sl
(2/1),
sl
(3/1), and
sl
(5/1). This involves the choice of the parameter
b
and the choice of the operators
I
3
(the third component of the weak left-handed isospin) and
U
(the weak hypercharge). These must commute, and are related to the electric charge by the usual formula
Q
=
I
3
+ ½
U
. In particular, taking
I
3
to be in its standard form in
su
(2) ⊂
sl
(5) ⊂
sl
(5/1) and requiring that
U
commute with color
su
(3) ⊂
sl
(5) ⊂
sl
(5/1) leaves three free parameters, two for the choice of
U
and one for the choice of
b
. We show that there are just two possible choices of these parameters yielding exactly all 32 quark and lepton charges: the Georgi-Glashow
U
∈
su
(5), corresponding to
U
(1,-⅔) and arbitrary
b
and
U
(0,⅓) ∉
su
(5), with
b
= 2. We provide a general construction of representations of
sl
(
n
/1) consisting exactly of sequences of generations of quarks and leptons.
Codon recognition rules in yeast mitochondria.
Authors: Bonitz S G , Berlani R , Coruzzi G , Li M , Macino G , Nobrega F G , Nobrega M P , Thalenfeld B E , Tzagoloff A
Published: May 2006

The mitochondrial genome of Saccharomyces cerevisiae codes for 24 tRNAs. The nucleotide sequences of the tRNA genes suggest a unique set of rules that govern the decoding of the mitochondrial genetic code. The four codons of unmixed fmilies are recognized by single tRNAs that always have a U in the wobble position of the anticodon. The codons of the mixed families are read by two different tRNAs. Codons terminating in a C or U are recognized by tRNAs with a G and codons terminating in a G or A are recognized by tRNAs with a U in the corresponding positions of the anticodons. There are two exceptions to these rules. In the AUN family for isoleucine and methionine, the isoleucine tRNA has a G and the methionine tRNA has a C in the wobble position. The tRNA for the arginine CGN family also has an A in the wobble position of the anticodon. It is of interest that the CGN codons have not been found in the mitochondrial genes sequenced to date. The simplified decoding system of yeast mitochondria allows all the codons to be recognized by only 24 tRNAs.
High-resolution fractionation of nucleosomes: minor particles, "whiskers," and separation of mononucleosomes containing and lacking A24 semihistone.
Authors: Levinger L , Varshavsky A
Published: May 2006

Staphyloccal nuclease digests of HeLa chromatin fractionated on low ionic strength nucleoprotein gels have been further analyzed by second-dimension DNA and protein gel electrophoresis. In vivo radioactive labeling of chromatin components and use of longer gels allowed a higher sensitivity and resolution than has been previously reported for this approach. A number of nonhistone protein spots and about 20 DNA spots can be detected in the mononucleosomal region of the second-dimension gel. In particular, there are three DNA spots identical in DNA size that correspond to three discrete kinds of core mononucleosomes resolved on the first-dimension nucleoprotein gel. Analysis of protein composition shows that the most rapidly migrating particle contains all four core histones but no A24 semihistone (A24 is a covalent conjugate of histone H2A and a specific nonhistone protein, ubiquitin), whereas the other two core mononucleosomes contain A24 semihistone. Thus, one can now quantitatively separate the A24-lacking core mononucleosomes from those containing A24, making it possible to directly address the question of whether A24 is associated with nucleosomes containing a specific subset of DNA sequences. Additional features of two-dimensional nucleoprotein-DNA patterns are "whiskers," which run slower than core mononucleosomes in the nucleoprotein dimension and both faster and slower than core-length DNA in the DNA dimension. In more extensive digests, "secondary whiskers" are observed, which run faster than core mononucleosomes in both dimensions and appear to coincide with previously described subnucleosomal particles SN7 and SN8 [Bakayev, V., Bakayeva, T. & Varshavsky, A. (1977) Cell 11, 619-629]. Possible mechanisms of whisker formation are discussed.
5,6-dichloro-1-beta-ribofuranosylbenzimidazole enhances premature termination of late transcription of simian virus 40 DNA.
Authors: Laub O , Jakobovits E B , Aloni Y
Published: May 2006

Short RNA chains initiating at the major promoter sites for simian virus 40 (SV40) late transcription are elongated to approximately 450 nucleotides in a molar ammount greater than that from any other region of the viral DNA. This conclusion is based on the following observations: (i) Transcriptional complexes isolated by Sarkosyl and by hypotonic leaching (minichromosomes) from nuclei of cells infected with SV40 as well as intact nuclei were pulse labeled in vitro with [alpha-32P]TUP and were observed to synthesize short RNA transcripts that hybridized predominantly to a SV40 DNA fragment spanning between 0.67 and 0.76 map units. (ii) In the presence of 5,6-dichloro-1-beta-D-ribofuranosylbenzimidazole (DRB), a drug known to accentuate premature transcriptional termination, accumulation of these short SV40 RNA chains was enhanced. When SV40-infected cells were pretreated with DRB and then labeled in vivo or in vitro, they synthesized short labeled viral RNAs that hydridized almost exclusively with the DNA fragment spanning between 0.67 and 0.76 map units. These observations suggest a mechanism in the regulation of SV40 late transcription.
Multienzyme complex for metabolic channeling in mammalian DNA replication.
Authors: Prem veer Reddy G , Pardee A B
Published: May 2006

In the DNA-synthesizing phase (S phase) of CHEF/18 Chinese hamster embryo fibroblast cells, six enzymes associated with DNA metabolism, including DNA polymerase (deoxynucleoside triphosphate:DNA deoxynucleotidyl-transferase, EC 2.7.7.7), were largely localized in the nuclear region (karyoplasts). By contrast, in quiescent and G1 phase cells these enzymatic activites were mainly absent from the nucleus and were recovered in the cytoplasmic portion (cytoplasts). These nuclear (but not cytoplasmic) enzymatic activities cosedimented rapidly on sucrose density gradients. Further, the rapidly sedimenting enzyme activities were unique to cells in S phase. An organized supramolecular structure that allows channeling of metabolites into DNA was demonstrated by kinetics of nucleotide incorporation. "Permeabilized" cells selectively channeled incorporation of ribonucleoside diphosphates into DNA in preference to deoxyribonucleoside triphosphates. Deoxyribonucleoside triphosphate incorporation occurred when ribonucleoside-diphosphate reductase (2'-deoxyribonucleoside-diphosphate: oxidized-thioredoxin 2'-oxidoreductase, EC 1.17.4.1) activity was abolished by hydroxyurea. Our interpretation is that during DNA replication, the nucleus contains a complex of DNA precursor-synthesizing enzymes juxtaposed with the "replication apparatus" comprising DNA polymerase, other enzymes, and structural proteins. Functional integrity of this structure is impaired when one of its essential components is inactivated. We propose the name "replitase" for this multienzyme complex for DNA replication and suggest that it incorporates precursors rapidly and efficiently. Possibly its assembly signals the initiation of the S phase of the cell cycle.
Rabbit reticulocyte initiation factor 2 contains two polypeptide chains of molecular weights 48,000 and 38,000.
Authors: Stringer E A , Chaudhuri A , Valenzuela D , Maitra U
Published: May 2006

Eukaryotic initiation factor 2 (eIF-20) purified from rabbit reticulocyte lysates consists of equimolar amounts of two polypeptide chains of Mr 48,000 and 38,000. Determination of the molecular weight of the native factor gave a value which is consistent with a Mr of 86,000 indicating that the factor is composed of one Mr 48,000 and one Mr 38,000 polypeptide. The purified factor exhibited all the binding activities characteristic of eIF-2. The factor formed ternary complexes with Met-tRNAfMet and GTP; it bound GDP to form a binary complex; and it also possessed the property of binding a wide variety of RNA species, including reoviral mRNA, phage T3 mRNA, rRNAs, and tRNA. Furthermore, the ternary complex formed by purified eIF-2 interacted with the 40S ribosomal subunit in the presence of AUG codon to form a 40S initiation complex. These results indicate that all binding activities attributed to eIF-2 are contained in the 48,000- and 38,000-dalton polypeptides.
Two control regions for eukaryotic tRNA gene transcription.
Authors: DeFranco D , Schmidt O , Söll D
Published: May 2006

Two Drosophila tRNALys genes with identical coding sequences were shown to transcribe with very different efficiences in nuclear extracts from Xenopus oocytes. The use of recombinant plasmids in which the 5'-flanking sequences of these genes were either "switched" or replaced by defined pBR322 sequences revealed two control regions for tRNA gene transcription. An internal control region comprising the mature tRNA coding sequence (and possibly its 3'-flanking sequences) is sufficient for transcription initiation, and an external control region comprising the 5'-flanking sequences represses this transcription. All transcripts have short leader sequences. Altered precursor tRNAs transcribed from truncated tRNALys genes (missing a single base pair in the acceptor stem) are not processed well in vitro.
Eukaryotic signal sequence transports insulin antigen in Escherichia coli.
Authors: Talmadge K , Stahl S , Gilbert W
Published: May 2006

We made a series of plasmids with unique Pst restriction sites within or near the DNA that encodes the penicillinase signal sequence. Inserted DNA can be read in all three frames both within and immediately after the signal sequence. We cloned Pst-terminated DNA copies of the structural information for rat proinsulin and preproinsulin into these plasmids, forming a large number of hybrid penicillinase (bacterial) and insulin (eukaryotic) signal sequences. We then compared the levels of insulin antigen in the Escherichia coli periplasm with those inside the cells. We conclude that either the bacterial or the eukaryotic signal is sufficient to transport rat insulin antigen into the periplasmic space.
Mobility, clustering, and transport of nerve growth factor in embryonal sensory cells and in a sympathetic neuronal cell line.
Authors: Levi A , Shechter Y , Neufeld E J , Schlessinger J
Published: May 2006

We have prepared a fluorescent conjugate of nerve growth factor (NGF) containing 8--10 rhodamine molecules attached to free carboxyl groups of the protein. This analogue retained full binding capacity toward NGF receptors, full antigenic properties, and the potency to stimulate the differentiation of embryonal chicken sensory ganglia cells in vitro. We have used this analogue to study the mobility and distribution of NGF receptors on embryonal chicken sensory cells from dorsal root ganglia and on a pheochromocytoma cell line (PC-12) that responds to NGF by differentiating along a neuronal pathway. The rhodamine conjugate of nerve growth factor (R-NGF) binds initially to diffusely distributed mobile receptors (D approximately 8 X 10(-10) cm2/sec) on immature sensory and PC-12 cells. At 37 degrees C, the NGF receptor complexes cluster and form immobile visible patches. These patches undergo endocytosis in a process that consumes metabolic energy. Methylamine blocks the formation of visible patches of NGF and the receptors remain dispersed and mobile at 37 degrees C. On differentiated chicken sensory cells, R-NGF binds to diffusely distributed mobile receptors and to aggregated immobile binding sites. These clusters are localized at the tip of the axon, along the axon, and in the main body. The NGF molecules that are internalized at the tip of the axon are transported retrogradely from the peripherey to the cell body.
Subpopulations of human peripheral granulocyes and monocytes express receptors for IgA.
Authors: Fanger M W , Shen L , Pugh J , Bernier G M
Published: May 2006

Receptors for the Fc portion of immunoglobin on human peripheral blood cells were enumerated by rosette formation with ox erythrocytes sensitized with rabbit IgG, IgA, and IgM. A large percentage of purified polymorphonuclear leukocytes and monocytes were found to express receptors for IgA. These receptors were also found to exist on a significantly greater percentage of lymphocytes than was previously observed. The receptors for IgA were specific, as verified by blocking studies using purified human immunogloblins. In addition, some polymorphonuclear leukocytes and monocytes were observed concomitantly to posses independent receptors for both IgG and IgA. These studies may indicate that IgA can cooperate with monocytes or polymorphonuclear leukocytes through receptors for IgA on these cells and perhaps mediate immune defense on mucosal surfaces. Initial studies on antibody-dependent cellular cytotoxicity suggested that IgA alone is ineffectual in supporting cytolysis by nonactivated human peripheral blood cells.
Isolation and partial chemical characterization of the IgG Fc receptor of human T lymphocytes and production of an antiserum.
Authors: Cunningham-Rundles C , Lawless D , Gupta S , Galanos C , Good R A
Published: May 2006

We report here the isolation of an IgG Fc receptor from normal human T lymphocytes. The purified receptor has a nonreduced and a reduced component of molecular weights 120,000 and 60,000, respectively, and it was functionally active in the in vitro blocking of rosette formation between T lymphocytes and IgG-coated ox erythrocytes. An antiserum raised to the Fc receptor and an isolated F(ab')2 fragment of this antiserum, also blocked rosette formation between T cells and IgG-coated ox erythrocytes. In contrast, rosette formation between T lymphocytes and IgM-coated ox or sheep erythrocytes was not blocked by the F(ab')2 fragment, demonstrating the marked specificity of this antiserum for the IgG Fc receptor. In addition, this antiserum did not block the Fc receptors of non-T cells, indicating that the T-cell IgG Fc receptor has unique antigenic determinants not shared with B cells.
Graded synaptic transmission between spiking neurons.
Authors: Graubard K , Raper J A , Hartline D K
Published: May 2006

Graded synaptic transmission occurs between spiking neurons of the lobster stomatogastric ganglion. In addition to eliciting spike-evoked inhibitory potentials in postsynaptic cells, these neurons also release functionally significant amounts of transmitter below the threshold for action potentials. The spikeless postsynaptic potentials grade in amplitude with presynaptic voltage and can be maintained for long periods. Graded synaptic transmission can be modulated by synaptic input to the presynaptic neuron.
A theoretical study of the structure of parathyroid hormone.
Authors: Zull J E , Lev N B
Published: May 2006

Theoretical analysis of the tertiary and secondary structure of parathyroid hormone was conducted. By combining interpretations from this analysis with chemical data available in the literature, certain structural features of the hormone are consistently predicted. The proposed model for the hormone contains two domains dominated by hydrophobic clustering of critical residues within each domain and separated by an exposed linker region. In the prediction of two domains with a linker region, the model is similar to that proposed by Fiskin et al. [Fiskin, A.M., Cohn, D.M. & Peterson, G.S. (1977) J. Biol. Chem. 252, 8261-8268], but it differs significantly in other respects. The proposed structural features are apparent in the bovine, human, and porcine species of hormone.
Nucleotide sequences of integrated Moloney sarcoma provirus long terminal repeats and their host and viral junctions.
Authors: Dhar R , McClements W L , Enquist L W , Vande Woude G F
Published: May 2006

Integrated Moloney murine sarcoma provirus (MSV) has direct terminal repeat sequences (TRS). We determined the nucleotide sequence of both 588-base-pair TRS elements and the adjacent host and viral junctions of an integrated MSV cloned in bacteriophage lambda. Sequences were identified corresponding to the tRNAPro primer binding site in genomic RNA and the reverse-transcribed minus strong stop DNA. Each 588-base-pair repeat contains putative sites for promoting RNA synthesis and RNA polyadenylylation. The first and last 11 nucleotides of the TRS are inverted with respect to each other, and the same four-nucleotide host sequence is found bracketing integrated MSV. Some similarities of TRS and prokaryotic insertion sequence elements are discussed.
Transformation of rat embryo fibroblasts by cloned polyoma virus DNA fragments containing only part of the early region.
Authors: Hassell J A , Topp W C , Rifkin D B , Moreau P E
Published: May 2006

Recombinant plasmids containing either the entire polyoma viral genome or one or the other of the two HindIII fragments of polyoma virus DNA were constructed and cloned in Escherichia coli X1776, and their DNAs were individually tested for the capacity to transform an established line of rat cells. The recombinant plasmids containing the entire polyoma genome and those containing the HindIII-1 fragment of polyoma DNA (45-1.4 map units) efficiently transform rat cells, whereas the plasmids containing the HindIII-2 fragment (1.4-45.0 map units) do not. The properties of many independent transformed cell lines established by infection with the cloned HindIII-1 fragment were determined. In contrast to the parent cell line, rat cells transformed with the cloned HindIII-1 fragment grow to high saturation densities, form colonies with high efficiency in dilute agar suspension, produce high levels of plasminogen activator, and display a disorganized arrangement of actin cables. By all criteria examined, these cells transformed by fragments are indistinguishable from cells transformed by whole polyoma viral DNA. Cellular DNA prepared from many HindIII-1 fragment-transformed cell lines was analyzed for the presence and arrangement of polyoma viral sequences by Southern blot-hybridization. In all cases examined, only those viral sequences contained within the HindIII-1 fragment of polyoma DNA were detected. These data establish a strong correlation between polyoma DNA sequences mapping within a restricted portion of the early region and the induction and maintenance of the transformed phenotype.
Bacteria mature preproinsulin to proinsulin.
Authors: Talmadge K , Kaufman J , Gilbert W
Published: May 2006

By inserting the rat preproinsulin gene into the bacterial prepenicillinase gene, we formed a variety of hybrid bacterial-eukaryotic signal sequences attached to proinsulin. Among these were the four following constructions: rat proinsulin attached to the entire penicillinase signal sequence and rat preproinsulin fused to all of, to half of, or only to the first four amino acids of the bacterial signal sequence. In all four cases, more than 90% of the rat insulin antigen appeared in the periplasmic space. By immunoprecipitation and determination of the amino acid sequences of the radiolabeled products, we show that the bacteria correctly process both the bacterial and the eukaryotic signal sequences of these hybrid proteins. The cleavage of the eukaryotic signal by bacterial peptidase, in this case, generates proinsulin.
Cytoplasmically made subunits of yeast mitochondrial F1-ATPase and cytochrome c oxidase are synthesized as individual precursors, not as polyproteins.
Authors: Lewin A S , Gregor I , Mason T L , Nelson N , Schatz G
Published: May 2006

At least three subunits of yeast mitochondrial F1-ATPase (ATP phosphohydrolase, EC 3.6.1.3) and at least two subunits of cytochrome c oxidase (ferrocytochrome c:oxygen oxidoreductase, EC 1.9.3.1) are synthesized outside the mitochondria and imported into the organelles as individual precursors that are between 2000 and 6000 daltons larger than the mature subunits. These precursors were shown to be primary translation products. Therefore, neither the five F1 subunits nor the four small cytochrome c oxidase subunits are synthesized as a single polyprotein.
Stopped-flow x-ray scattering: the dissociation of aspartate transcarbamylase.
Authors: Moody M F , Vachette P , Foote A M , Tardieu A , Koch M H , Bordas J
Published: May 2006

A combination of stopped-flow and x-ray scattering techniques was used to study the dissociation of aspartate transcarbamylase (carbamoylphosphate:L-aspartate carbamoyltransferase, EC 2.1.3.2) with a 2:1 excess of p-chloromercuribenzenesulfonic acid (the ratio being calculated on a basis of reactive sites), in the presence and absence of the transition state analogue N-(phosphonacetyl)-L-aspartate. At 10 mg of protein per ml, the scattering curves allowed some details of the reaction to be followed with a time resolution down to 1 sec. The curves showed not only the dissociation of the enzyme complex but also the formation of the subunits. These results show that, with present facilities, x-ray scattering could be used to study dissociation or reassociation reactions with a time resolution of the order of 100 msec.
Compositional domain structure in phosphatidylcholine--cholesterol and sphingomyelin--cholesterol bilayers.
Authors: Snyder B , Freire E
Published: May 2006

the lateral distribution of cholesterol in phospholipid bilayers has been investigated through a method of Monte Carlo calculations, using interaction energies deduced from calorimetric results for cholesterol-phospholipid mixtures. Analysis of computer-generated bilayer configurations allows calculation of the spatial localization and relative abundance of distinct regions of varying cholesterol content along the plane of the bilayer. An interfacial phospholipid region between cholesterol-bound and cholesterol-free domains is found to extend one lipid beyond the cholesterol-bound domain for mixtures of cholesterol with palmitoyl sphingomyelin, lignoceroyl sphingomyelin, and dipalmitoyl phosphatidylcholine. The results indicate that the degree of nonideality in the mixing of cholesterol is dependent on fatty acid chain length and that cholesterol mixes more ideally in sphingomyelins than in phosphatidylcholines of equal chain length. It is found that at approximately 20 mol % cholesterol the cholesterol-rich areas suddenly become connected, forming a network that extends over the entire bilayer. This change in the lateral connectivity of the cholesterol-rich domains occurs over a narrow concentration interval and is presumably responsible for the abrupt change in the lateral diffusion coefficient observed at this concentration.
Prevalent deficiency in tumor cells of cycloheximide-induced cycle arrest.
Authors: Medrano E E , Pardee A B
Published: May 2006

Mammalian cell growth is regulated by a process that is completed at a restriction point in the late G1 part of the cycle. This process is highly sensitive to serum concentration and to moderate inhibition of protein synthesis by cycloheximide (CHM) or other agents. We have proposed that a cell must accumulate a labile protein in a critical amount before events related to its DNA synthesis can start. The accumulation of this protein requires conditions suitable for growth, including sufficient amounts of serum-derived factors. An important criterion for attributing a major role to such a regulatory mechanism is that cells whose growth control is modified--e.g., by mutation--should be defective in this process. Cells of this kind are produced by tumorigenic transformation. We show here that mouse 3T3 cells, human fibroblasts, and Chinese hamster CHEF/18 cells have stringent G1 growth control by CHM. In contrast, tumorigenic lines obtained from these cells by transformation with varius agents (DNA tumor virus, RNA tumor virus, chemical carcinogens) or spontaneously all showed relaxed growth control under the influence of CHM. In these lines, growth control was relaxed to different degrees; some lines were held in G1 by a combination of low serum concentration and CHM, but others were not. Serum concentration showed a synergistic effect with CHM. Low serum concentrations did not limit growth only by affecting the rate of protein synthesis. The labile-protein mechanism is likely to be basic to growth control by serum factors. Transformed tumorigenic cells in general may have relaxed this mechanism.
Most sequence differences between the genomes of the Akv virus and a leukemogenic Gross A virus passaged in vitro are located near the 3' terminus.
Authors: Buchhagen D L , Pedersen F S , Crowther R L , Haseltine W A
Published: May 2006

The 70S genomic RNA of nonleukemogenic AKR(Akv) virus was compared to that of an in vitro passaged, cloned, leukemogenic Gross A virus by fingerprint and sequence analysis. Fifty-seven of the large ribonuclease T1-resistant oligonucleotides of each virus have the same electrophoretic mobility and sequence. Thirteen large ribonuclease T1 oligo nucleotides are unique to the Gross A virus, whereas five are unique to Akv. Four of the oligonucleotides unique to each virus are related by one or two simple base changes. Five of the differences in oligonucleotides are located in the region of the genome that codes for the gag and pol genes. Eight of the differences are located near the 3' poly(A) terminus of the virus. The origins and biological consequences of these differences are discussed.
Asymptotic form for random walk survival probabilities on three-dimensional lattices with traps
Authors: Weiss George H.
Published: May 2006

The problem of calculating statistics of time-to-trapping of a random walker on a trap-filled lattice is of interest in solid state physics. Several authors have suggested approximate methods for calculating the average survival probabilities. Here, an exact asymptotic form for the probability that an
n
step random walk visits

S
n

distinct sites is used to ascertain the validity of a simple approximation suggested by Rosenstock. For trap concentrations below 0.05, the relative error in using Rosenstock's approximation is less than 10%.
Asymptotic behavior of atomic and molecular wave functions
Authors: Katriel J. , Davidson E. R.
Published: May 2006

The asymptotic form of bound-state wave functions is derived by analytic continuation of asymptotic scattering-state wave functions. The result is also regorously derived by using an approach that is independent of scattering theory. One aspect of the result is that the
N
electron wave function becomes the lowest accessible exact wave function for the remaining
N
— 1 electrons when one electron is far away from all the nuclei. This shows that the recently developed extended Koopmans' procedures are in principle exact for the first ionization energy.
Characterization of rat calcitonin mRNA.
Authors: Amara S G , David D N , Rosenfeld M G , Roos B A , Evans R M
Published: May 2006

A chimeric plasmic containing cDNA complementary to rat calcitonin mRNA has been constructed. Partial sequence analysis shows that the insert contains a nucleotide sequence encoding the complete amino acid sequence of calcitonin. Two basic amino acids precede and three basic amino acids follow the hormone sequence, suggesting that calcitonin is generated by the proteolytic cleavage of a larger precursor in a manner analogous to that of other small polypeptide hormones. The COOH-terminal proline, known to be amidated in the secreted hormone, is followed by a glycine in the precursor. The cloned calcitonin DNA was used to characterize the expression of calcitonin mRNA. Cytoplasmic mRNAs from calcitonin-producing rat medullary thyroid carcinoma lines and from normal rat thyroid glands contain a single species, 1050 nucleotides long, whch hybridizes to the cloned calcitonin cDNA. The concentration of calcitonin mRNA sequences is greater in those tumors that produce larger amounts of immunoreactive calcitonin. RNAs from other endocrine tissues, including anterior and neurointermediate lobes of rat pituitary, contain no detectable calcitonin mRNA.
Collagen-tailed and hydrophobic components of acetylcholinesterase in Torpedo marmorata electric organ.
Authors: Bon S , Massoulié J
Published: May 2006

We have distinguished three fractions of acetylcholinesterase (AcChoE; acetylcholine acetylhydrolase, EC 3.1.1.7) from Torpedo marmorata electric organs, according to their solubilization characteristics. The low-salt-aggregating collagen-tailed forms are soluble in high-salt buffers; their hydrodynamic properties ae not modified in the presence of detergents. They constitute the A fraction, which amounts to about a third of the tissue's AcChoE activity. The low-salt-soluble (LSS) and detergent-soluble (DS) fractions are not sensitive to ionic strength and collagenase. In the presence of nonionic detergents or bile salts, both fractions behave as a monodisperse "6.3S" form, the properties of which have been investigated mostly in the case of Triton X-100. Disulfide bond reduction dissociates the detergent form into a smaller "5S" form. These two forms are thought to be, respectively, detergent-associated dimers and monomers. In the absence of detergent, the LSS fraction is polydisperse: it contains a major 8S component, 11S and 14S components, and faster-sedimenting aggregates, which appear to represent dimers, tetramers, and higher polymers. The heterogeneity of the 8S component in gel filtration suggests that it also contains variable noncatalytic elements. Upon removal of the detergent the DS fraction forms ill-defined aggregates. Trypsin induces quaternary rearrangements of part of the 8S component into 11S and 14S components, which are still convertible into the detergent form; therefore trypsin probably digests noncatalytic elements. Pronase and proteinase K, on the other hand, convert the enzyme into a dimeric form, G2, that does not interact with detergents, probably by cleaving a minor fragment of the subunit that is involved in hydrophobic interactions.
Excretion of hepatitis B surface antigen particles from mouse cells transformed with cloned viral DNA.
Authors: Dubois M F , Pourcel C , Rousset S , Chany C , Tiollais P
Published: May 2006

A plasmid containing two cloned hepatitis B virus genomes in a tandem head-to-tail arrangement has been introduced into mouse fibroblasts by using cotransformation with the cloned herpes simplex virus thymidine kinase gene. Several copies of the plasmid were integrated into high molecular weight cellular DNA. The original tandem structure of the hepatitis B virus DNA was conserved. Hepatitis B surface antigen was synthesized by all the 15 clones examined. The other viral antigens were not detected. The surface antigen was excreted into the cell culture medium as particles having the same characteristics as those found in human serum. It is estimated that 2-4 X 10(4) particles were produced per mouse cell per 24 hr in two clones. This value corresponds to approximately 2-4 X 10(6) surface antigen polypeptides per cell per 24 hr.
Eukaryotic DNA segments capable of autonomous replication in yeast.
Authors: Stinchcomb D T , Thomas M , Kelly J , Selker E , Davis R W
Published: May 2006

A selective scheme is presented for isolating sequences capable of replicating autonomously in the yeast Saccharomyces cerevisiae. YIp5, a vector that contains the yeast gene ura3, does not transform a ura3 deletion mutant to Ura+. Hybrid YIp5-Escherichia coli DNA molecules also fail to produce transformants. However, collections of molecular hybrids between YIp5 and DNA from any of six eukaryotes tested (S. cerevisiae, Neurospora crassa, Dictyostelium discoideum Ceanhorabditis elegans, Drosophila melanogaster, and Zea mays) do transform the deletion mutant. The Ura+ transformants grow slowly, are unstable under nonselective conditions, and carry the transforming DNA as autonomously replicating, supercoiled circular molecules. Such a phenotype is qualitatively identical to that of strains transformed by molecules containing a yeast chromosomal origin of replication. Thus, these DNA hybrid molecules may contain eukaryotic origins of replication. The isolated sequences may be useful in determiing the signals controlling DNA replication in yeast and in studying both DNA replication and transformation in other eukaryotic organisms.
Hormonal and immunological aspects of the phylogeny of sex steroid binding plasma protein.
Authors: Renoir J M , Mercier-Bodard C , Baulieu E E
Published: May 2006

Sex steoid binding plasma protein (Sbp) in man and in monkeys binds the androgens dihydrotestosterone and testosterone and the estrogen estradiol with high affinity (Kd approximately 0.5, 1, and 2 nM, respectively). Detailed studies of steroid binding specificity give the same results in all primates, except that in humans and chimpanzees estrone does not compete for dihydrotestosterone binding. In other mammals, Sbps of Artiodactyla and Lagomorpha have the same range of affinities for androgens but they do not bind estradiol to any significant extent (Kd > 280 nM). The dog has an unusual Sbp (Kd for dihydrotestosterone, 7.1 nM; for estradiol, 125 nM), and rodents do not have a specific dihydrotestosterone-binding plasma protein. Gel filtration and immunoelectrophoretic experiments have been performed with a monospecific antiserum against human Sbp. The results indicate variable crossreactivities with Sbps of primates (from complete in chimpanzee and gorilla to weak in Prosimii). No crossreaction was observed with specific androgen-binding plasma proteins of other species. These results suggest the evolutionary emergence of bifunctional Sbp.
Genomic organization of rat prolactin and growth hormone genes.
Authors: Chien Y H , Thompson E B
Published: May 2006

Five overlapping cloned DNAs containing the rat prolactin gene and its flanking sequences, as well as one cloned DNA containing the rat growth hormone gene and its flanking sequences, were isolated from a chromosomal DNA library. They were characterized by restriction enzyme mapping and electron microscopy. In each gene, the structural gene sequence coding for mature mRNA of a length of about 1 kilobase is split into at least five segments by a minimum of four intervening sequences. The two genes are similar in the length and organization of their coding regions, consistent with the suggestion that they are derived from a common ancestral gene. However, the two genes differ greatly in the lengths of their intervening sequences. That leads to a total gene length of 10 kilobase pairs for the prolactin and 2.1 kilobase pairs for the growth hormone gene. At least one intervening sequence appears to be in the 5' nontranslated regions of the prolactin and growth hormone mRNA coding sequences.
beta-Endorphin: stability, clearance behavior, and entry into the central nervous system after intravenous injection of the tritiated peptide in rats and rabbits.
Authors: Houghten R A , Swann R W , Li C H
Published: May 2006

Rabbits and rats were given intravenous injections of tritiated human beta-endorphin. The levels of beta-endorphin were followed by the decrease in radioactivity in the plasma of rats or rabbits and by the increase in radioactivity in the cerebrospinal fluid of the rabbit. The results were identical with the tritium label on either tyrosine-1 or -27. The plasma distribution times were 2 and 5 min in the rat and rabbit, respectively, with a later clearance time of approximately 1-8 hr. In the rat, approximately 50% of the radioactivity in the plasma was found to be intact human beta-endorphin 45 min after injection. Radioactivity appeared in the cerebrospinal fluid of the rabbit within 30 sec after injection and reached a plateau in approximately 60-90 min after injection. Approximately 75% of the radioactivity in the cerebrospinal fluid of the rabbit was intact human beta-endorphin. In the brain hemispheres of the rat and the rabbit, the only significant radiolabeled product was found to be radioactive tyrosine. Moreover, rat plasma levels of beta-endorphin decreased dramatically after hypophysectomy, which only slightly lowered the levels in the brain. It appears that beta-endorphin, upon entry into the plasma, is either not significantly taken up into the brain or is broken down with extreme rapidity upon entry into the brain, although it apparently does enter the cerebrospinal fluid.
Amino acid sequence of the T4 DNA helix-destabilizing protein.
Authors: Williams K R , LoPresti M B , Setoguchi M , Konigsberg W H
Published: May 2006

The primary structure of the T4 single-stranded DNA-binding protein coded by gene 32 has been determined by manual and autoated sequencing of peptides derived from partial proteolysis, cyanogen bromide cleavage, and digestion with trypsin, chymotrypsin, and staphylococcal protease. Tryptic digestion of citraconylated or succinylated gene 32 protein yields five peptides containing 4, 27, 42, 65, and 163 residues, which can be separated by Sephadex chromatography. Each of the tryptic peptides was subjected to automated sequencing and, if necessary, more extensive cleavage. The intact protein contains 301 amino acids, has a molecular weight of 33,487, and can be specifically cleaved at lysines 21 and 253 by limited trypsin digestion. Previous studies have shown that the "B" region (residues 1-21), which has a charge of +4, is important for the protein-protein interactions involved in gene 32 protein self-association and cooperaive binding to single-stranded DNA. The "A" region (residues 254-301) has been implicated in controlling the helix-destabilizing "activity" of gene 32 protein and in interacting with other T4 DNA replication proteins. The A region has a charge of -10 and, in addition, contains two unusual stretches of four serine residues separated by glycine 284. The region between positions 73 and 115 contains 75% of the tyrosine residues and may be important for DNA binding.
Mapping of transforming region of the Harvey murine sarcoma virus genome by using insertion-deletion mutants constructed in vitro.
Authors: Wei C M , Lowy D R , Scolnick E M
Published: May 2006

Circular DNA intermediates of Harvey murine sarcoma virus (Ha-MuSV) have been cloned in lambda gtWES . lambda B and shown to be capable of transforming mouse NIH 3T3 cells [Hager, G. L., Chang, E. H., Chan, H. W., Garon, C. F., Israel, M. A., Martin, M. A., Scolnick, E. M. & Lowy, D. R. (1979) J. Virol. 31, 795-809]. By using the cloned Ha-MuSV DNA insert as a parental genome, we have constructed a series of insertion-deletion mutants by inserting an octomer containing the Sal I linker sequence (G-G-T-C-G-A-C-C) into various regions of the Ha-MuSV genome after partial digestion with Hae III. After ligation into lambda gtWES . lambda B-Sal I vector molecules, the mutant Ha-MuSV DNAs were cloned. Fourteen insertion-deletion mutants have been mapped by restriction enzyme digestion, and their biological activities have been correlated with the locations of mutations. The mutants whose lesion mapped within 3.0 kilobases (kb) frm the 3'-end of the Ha-MuSV genome retained full transforming ability. The mutants containing the Sal I linker insertion at 0.4 or 1.5 kb from the 5'-end also retained transforming ability, but the number of foci induced by the DNAs in transfection assays was greatly reduced. However, a mutant containing a deletion of 1.5 kb at the 5'-end and a mutant with a deletion of the sequences between 1.0 and 1.5 kb from the 5'-end completely lost their transforming potential. A model for the transforming region of Ha-MuSV is discussed. Furthermore, because Ha-MuSV sequences can be rescued from the mouse cells transformed by these mutants using Moloney murine leukemia virus as a helper virus, it implies that the in vitro modified DNAs may be converted into genuine mutant viruses.