bluuebunny/crossref_metadata_2025 huggingface dataset:
Differentiation and virus expression in BALB/Mo mice: endogenous Moloney leukemia virus is not activated in hematopoietic cells.
Authors: Fiedler W , Nobis P , Jähner D , Jaenisch R
Published: May 2006

The endogenous Moloney leukemia virus (M-MuLV) in the BALB/Mo substrain of mice is activated during the first week after birth. Virus replication occurs in cells of the lymphatic system. Lymphoid cells therefore represent the target cells for virus replication and leukemic transformation. To investigate whether virus activation occurs during lymphoid cell differentiation, hematopoietic stem cells carrying the endogenous Mov-1 genome were transplanted to sublethally irradiated BALB/c mice. Effective colonization of the recipients was demonstrated by Southern DNA hybridization. No activation of the endogenous Mov-1 genome occurred during a 4-month observation period after the transplantation. Thus the first step in development of disease in BALB/Mo mice involves activation of the Mov-1 locus in a nonhematopoietic cell followed by superinfection of lymphatic cells and subsequent virus replication and virus spread.
Synthesis of fucosyl-containing glycoproteins of the vitelline coat in oocytes of Ciona intestinalis (Ascidia).
Authors: Rosati F , Cotelli F , De Santis R , Monroy A , Pinto M R
Published: May 2006

The sperm receptors of the ascidian oocyte are located at the outer surface of the vitelline coat (formerly called the chorion). The fucose residues are the receptor's most important components for sperm recognition and binding. We asked whether the fucosyl-containing glycoproteins of the vitelline coat are a product of the oocyte, the follicle cells, or the test cells. Ovaries of Ciona intestinalis were injected with L-[3H]fucose and the progress of its incorporation was followed by using autoradiography and sodium dodecyl sulfate/polyacrylamide gel electrophoresis of the injected gonads and of the isolated vitelline coats. We found that incorporation of fucose begins within the vitellogenic oocytes, and fucose slowly accumulates in the differentiating vitelline coat. At no time could fucose incorporation be detected in the follicle cells or in the test cells. Sodium dodecyl sulfate/polyacrylamide gel electrophoresis of vitelline coats prepared from the injected ovaries showed fucose incorporation into the same three glycoproteins present in vitelline coats from mature oocytes and identified by their affinity for 125I-labeled fucose-binding protein [Pinto, M. R., De Santis, R., D'Alessio, G. & Rosati, F. (1981) Exp. Cell Res. 132, 289-295]. A radioactive band not found in the mature oocyte was also present.
Assignment of the gene for beta 2-microglobulin (B2m) to mouse chromosome 2.
Authors: Cox D R , Sawicki J A , Yee D , Appella E , Epstein C J
Published: May 2006

We have assigned the gene (B2m) coding for murine beta 2-microglobulin (B2M) to mouse chromosome 2 by using a novel panel of Chinese hamster-mouse somatic cell hybrid clones. Because of 35 independent primary hybrids used in this study were derived from two types of feral mice, each with a different combination of Robertsonian translocation chromosomes, as well as from mice with a normal complement of acrocentric chromosomes, analysis of 16 selected mouse enzyme markers provided data on the segregation of all 20 mouse chromosomes in these hybrids. Mouse B2M was identified in cell hybrids by immunoprecipitation with a species-specific anti-mouse B2M antiserum followed by two-dimensional polyacrylamide gel electrophoresis of the immunoprecipitated polypeptides. Enzyme analysis of the segregant clones excluded all chromosomes for B2m assignment except mouse chromosome 2, and karyotype analysis of nine informative hybrid clones confirmed the assignment of B2m to this chromosome. These results demonstrate that, in the mouse, as in man, B2m is not linked to the major histocompatibility or immunoglobulin loci.
Cloned cDNA sequences of the hypoxanthine/guanine phosphoribosyltransferase gene from a mouse neuroblastoma cell line found to have amplified genomic sequences.
Authors: Brennand J , Chinault A C , Konecki D S , Melton D W , Caskey C T
Published: May 2006

Cloned cDNA sequences of the murine hypoxanthine/guanine phosphoribosyltransferase (HPRT; EC 2.4.2.8) gene have been isolated by using a mouse neuroblastoma cell line containing increased levels of a variant HPRT protein. We have used these sequences as probes to demonstrate that protein overproduction in this cell line is a consequence of at least a 20-fold increase in HPRT mRNA levels resulting from approximately 50-fold amplification of HPRT genomic sequences. The largest cDNA insert so far characterized represents about 70% of the HPRT mRNA sequence. This cDNA is shown to possess regions of homology with mRNA and DNA from Chinese hamster, baboon, and human, thus facilitating detailed analysis of this locus in these four species.
Tolerance of thymic cytotoxic T lymphocytes to allogeneic H-2 determinants encountered prethymically: evidence for expression of anti-H-2 receptors prior to entry into the thymus.
Authors: Morrissey P J , Kruisbeek A M , Sharrow S O , Singer A
Published: May 2006

This study has assessed the possibility that anti-H-2 receptors are expressed on T-cell precursors prior to their entry into the thymus. Parental strain A thymus was transplanted into either normal or thymectomized (A x B)F1 mice which were then irradiated and reconstituted with strain A bone marrow. The cells repopulating the engrafted strain A thymus were shown to be of donor bone marrow origin. Thus, strain A thymocytes were differentiating within a syngeneic thymus, after exposure to allogeneic strain B major histocompatibility complex (MHC) determinants of the irradiated F1 host. The cells repopulating the engrafted thymus were assessed for their ability to generate alloreactive cytotoxic T lymphocyte responses and were found to be specifically tolerant to allogeneic strain B MHC determinants. This tolerance existed in the absence of detectable suppression and in the absence of detectable strain B MHC determinants intrathymically. These data are most consistent with the concept that precursor T cells express anti-MHC receptors prior to their entry into the thymus and that exposure to MHC determinants prethymically results in their functional inactivation.
mRNA for surface immunoglobulin gamma chains encodes a highly conserved transmembrane sequence and a 28-residue intracellular domain.
Authors: Tyler B M , Cowman A F , Gerondakis S D , Adams J M , Bernard O
Published: May 2006

To probe the structure of the gamma heavy chain of membrane IgG and the mRNA and gene segments that encode it, we have analyzed cDNA clones derived from a gamma 1 membrane RNA of B lymphoma 2PK-3. The nucleotide sequence of the clones indicated that membrane gamma 1 chains bear a COOH-terminal 71-residue segment that is absent from secretory gamma 1 chains. This terminus includes a 26-residue hydrophobic transmembrane region homologous to that of membrane mu chains and, significantly, a 28-residue intracellular domain found only on gamma chains. The extra domain suggests that receptor IgG, on memory B cells, may generate a different signal on binding antigen than does receptor IgM, on virgin B cells. The gamma 1 membrane terminus is encoded by two gene segments 1.5 and 2.4 kilobase pairs downstream from the C gamma 1 gene, and homologous segments occur 3' to the C gamma 2a and C gamma 3 genes. Small amounts of membrane gamma mRNAs persist in plasmacytomas secreting IgG1, IgG2a, or IgG2b, suggesting that competition between alternative RNA processing pathways governs the synthesis of membrane and secretory gamma chain mRNAs.
Nonselective expression of simian virus 40 large tumor antigen fragments in mouse cells.
Authors: Reddy V B , Tevethia S S , Tevethia M J , Weissman S M
Published: May 2006

To understand the role of various functional domains of simian virus 40 early tumor antigens, we have cloned and introduced into mouse cells portions of early simian virus 40 DNA. Two types of truncated large tumor antigen (33 and 12.3 kilodaltons), as well as small tumor antigen, were identified by immunoprecipitation. Both truncated large tumor antigens have been found to be overproduced with respect to the small tumor antigen, although the 12.3-kilodalton truncated large tumor antigen was more stable than the 33-kilodalton one. Nonviral 53-kilodalton protein was not found associated with either truncated large tumor antigen in immunoprecipitations.
gamma and alpha chains of human fibrinogen possess sites reactive with human platelet receptors.
Authors: Hawiger J , Timmons S , Kloczewiak M , Strong D D , Doolittle R F
Published: May 2006

Fibrinogen, a clottable plasma protein, agglutinates both prokaryotic cells (e.g., staphylococci) and eukaryotic cell fragments (e.g., platelets) through interaction with specific receptors. To identify the region of the fibrinogen molecule responsible for its interaction with human platelets, we prepared polypeptide chain subunits (alpha, beta, and gamma) of human fibrinogen by reduction and carboxymethylation. A mixture of the chains induced aggregation (clumping) of human platelets separated from plasma proteins and treated with ADP. When individual chains of fibrinogen were tested, gamma-chain multimers caused platelet aggregation at a molar concentration comparable with that of intact human fibrinogen. The beta chain remained inactive, and the alpha chain was 1/4th to 1/5th as reactive as the gamma chain. Monospecific antibody fragments against the gamma chain inhibited binding of 125I-labeled fibrinogen to the human platelet receptor and blocked aggregation of platelets induced by ADP in the presence of fibrinogen or gamma-chain multimers. These results indicate that the gamma chain of human fibrinogen bears the main site for interaction with the platelet receptor.
Fluid transport across retinal pigment epithelium is inhibited by cyclic AMP.
Authors: Miller S S , Hughes B A , Machen T E
Published: May 2006

Fluid transport across the retinal pigment epithelium (bullfrog) has been measured. These experiments were carried out by using a capacitance probe technique and a water-impermeable chamber that allowed the measurements to be made with an accuracy of 0.5-1.0 nl/min. With identical Ringer's solution on both sides of the epithelium, and in the absence of a hydrostatic driving force, the direction of net fluid movement is from the retina to the choroid (absorption). The net transport rate, approximately 10 nl/min (4.8 microliters/cm2 . hr), is comparable to that observed in other amphibian epithelia. It is reduced to zero by the mitochondrial uncoupler 2,4-dinitrophenol but is relatively unaffected by ouabain, which inhibits the Na+/K+-pump located on the apical membrane of this epithelium. A significant decrease in net fluid absorption was produced by dibutyryl cAMP and 3-isobutyl-1-methylxanthine (a potent phosphodiesterase inhibitor). This cAMP-dependent fluid transport may be an important mechanism for controlling the fluid volume in the subretinal space.
Amino acid sequence homology between pig heart lipoamide dehydrogenase and human erythrocyte glutathione reductase.
Authors: Williams C H , Arscott L D , Schulz G E
Published: May 2006

Extensive amino acid sequence homology has been found between nine tryptic peptides of pig heart lipoamide dehydrogenase (NADH:lipoamide oxidoreductase, EC 1.6.4.3] and the sequence of human erythrocyte glutathione reductase [NAD(P)H:glutathione oxidoreductase, EC 1.6.4.2]. The average homology is 40%. Six lipoamide dehydrogenase peptides are homologous with segments of the two parts of the FAD domain of glutathione reductase, one with the NADPH domain, and two with the interface domain. Thus, the homology extends throughout the molecule.
DNA precursor pool: a significant target for N-methyl-N-nitrosourea in C3H/10T1/2 clone 8 cells.
Authors: Topal M D , Baker M S
Published: May 2006

Synchronized C3H/10T1/2 clone 8 cells were treated in vitro with a nontoxic dose of N-methyl-N-nitrosourea during their S phase. Chromatographic isolation of the deoxyribonucleotide DNA precursor pool and measurement of the precursor content per cell showed that a nucleic acid residue in the precursor pool is 190-13,000 times more susceptible to methylation than a residue in the DNA duplex, depending on the site of methylation. This conclusion comes from measurements indicating that, for example, the N-1 position of adenine in dATP is 6.3 times more methylated than the same position in the DNA, even though the adenine content of the pool is only a fraction (0.0005) of the adenine content of the DNA helix. The comparative susceptibility between pool and DNA was found to vary with the site of methylation in the order the N-1 position of adenine greater than phosphate greater than the N-3 position of adenine greater than the O6 position of guanine greater than the N-7 position of guanine. The significance of these results for chemical mutagenesis and carcinogenesis is discussed.
The 48-base-long primordial building block of immunoglobulin light-chain variable regions is complementary to the primordial building block of heavy-chain variable regions.
Authors: Ohno S , Matsunaga T
Published: May 2006

The ancestral gene for immunoglobulin light-chain variable regions (Ig VLs) of the kappa as well as the lambda class apparently arose from about 12 tandem repeats of the 48-base-long primordial building block sequence TCT-TGC-GCA-GTA-AGT-CCA-CTC-CAG-GTC-ATA-TCC-AGT-CAG-GCT-GCT-GAA. Even today, amino acid residues 67 to 82 of each Ig V kappa L are still specified by a direct descendant in toto of the above-noted primordial building block, whereas amino acid residues 14 to 25 are invariably specified by its truncated copy. The Ig VL primordial building block presently identified is 100% complementary to the Ig VH (heavy-chain variable region) primordial building block previously identified. In the recognition of specific antigenic determinants by antibodies, Ig VL and Ig VH of light-chain--heavy-chain dimers have to complement each other. It is perhaps fitting that the primordial building blocks of the two are represented by the complementary strands of the same 48-base-pair-long DNA sequence.
Sequence-specific endonuclease BamHI: relaxation of sequence recognition.
Authors: George J , Chirikjian J G
Published: May 2006

The effect of glycerol on the specificity of DNA cleavage by the restriction endonuclease BamHI has been examined. In addition to the canonical G decreases from G-A-T-C-C site, BamHI cuts DNA at several sites that we have named noncanonical BamHI.1 sites. The number of BamHI.1 sites in simian virus 40 and pBR322 was determined to be 13 for each DNA. Cutting sites determined by DNA sequence analysis include G decreases from G-A-A-C-C, G decreases from G-C-T-C-C, G decreases from G-G-T-C-C, and G-A-A-T-C-C with the complementary strand sequence assignments of G-G-T-T-C-C, G-G-A-G-C-C, G-G-A-C-C-C, and G-G-A-T-T-C. The relaxation in specificity was related to hydrogen bond acceptor and donor sites in the recognition sequence, in an attempt to generate a model of BamHI recognition of cognate sites in DNA.
Nerve growth factor: activation of the classical complement pathway by specific substitution for component C1-.
Authors: Boyle M D , Young M
Published: May 2006

The interaction of homogeneous preparations of mouse submandibular gland nerve growth factor (NGF) with the classical complement pathway was studied. NGF was found to be capable of carrying out the enzyme activities of the first component (C1-) of the classical complement pathway (i.e., the cleavage of zymogen C4 and C2). NGF would not substitute for any other classical pathway component, C2-C9. The C1(-)-like activity of NGF was inhibited by human C1- inactivator. This interaction of NGF with the complement system may account for the previously described ability of NGF to accelerate the rate of contraction of experimentally induced wounds.
Mechanism of polypeptide chain initiation in eukaryotes and its control by phosphorylation of the alpha subunit of initiation factor 2.
Authors: Siekierka J , Mauser L , Ochoa S
Published: May 2006

Earlier, we isolated eukaryotic initiation factor 2 (eIF-2)-stimulating protein (SP) as a homogeneous complex with eIF-2 (eIF-2-SP) and showed that, in the presence of Mg2+, eIF-2-SP promotes formation of a ternary complex with GTP and eukaryotic initiator methionyl tRNA (Met-tRNAi) (eIF-2-GTP-Met-tRNAi) catalytically. We now show that SP-bound eIF-2 exchanges with eIF-2 (eIF-2 exchange). Furthermore, in the presence of Mg2+, eIF-2-SP catalyzes the exchange of eIF-2-bound [3H]GDP with unlabeled GDP or GTP (GDP exchange) and the release of [3H]GDP when the ternary complex is formed from eIF-2-[3H]GDP, GTP, and [35S]Met-tRNAi. All these reactions are blocked by alpha-subunit, but not by beta-subunit, phosphorylation of eIF-2. The eIF-2 and GDP exchanges are compatible with the reaction eIF-2-GDP + SP in equilibrium EIF-2-SP + GDP reminiscent of the exchange between the Tu and Ts components of prokaryotic elongation factor 1 (EF-Tu and EF-Ts, respectively) EF-Tu-GDP + EF-Ts in equilibrium EF-Tu-EF-Ts + GDP. Due to the high affinity of GDP (approximately 100 times greater than that of GDP) for eIF-2, 40S (eIF-2-GTP-Met-tRNAi-40S) to 80S (Met-tRNAi-mRNA-80S) initiation complex conversion, which is accompanied by GTP hydrolysis, probably releases eIF-2 as eIF-2-GDP. Our results suggest that, in the presence of Mg2+, GDP binding restricts the availability of eIF-2 for chain initiation and that SP relieves this restriction in a catalytic fashion, provided that the alpha subunit of eIF-2 is not phosphorylated.
Extrachromosomal mutator inducing point mutations and deletions in mitochondrial genome of fission yeast.
Authors: Seitz-Mayr G , Wolf K
Published: May 2006

We report the isolation and characterization of a mutator mutant in the fission yeast Schizosaccharomyces pombe. This mutator is of extrachromosomal, very likely mitochondrial, inheritance and acts exclusively on mitochondrial mtDNA. It greatly enhances the frequency of spontaneous mitochondrial drug-resistance mutants compared to the wild type, but it is not obligatory for their occurrence. In contrast, mitochondrial respiratory deficient mutants can only be isolated from mutator strains. It could be shown that this mutator induces point mutations as well as deletions in the mitochondrial genome which lead to respiratory deficiency. This mutator might prove to have a novel function encoded by the mtDNA.
Group selection for a polygenic behavioral trait: a differential proliferation model.
Authors: Crow J F , Aoki K
Published: May 2006

Conditions for natural selection to increase a polygenic behavioral trait are derived for a model in which the population is divided into a very large number of partially isolated groups of variable and varying size. Specifically, we consider an altruistic trait that is deleterious to the individual but raises the mean fitness of the group. We assume, for each generation, that all groups have the same proportion of males, k, at the time of migration and that each group contributes Mf females and Mm males to a pool of migrants, from which Mf females and Mm males are randomly parceled out to each group. This assumption ensures that at equilibrium between random drift and a low level of migration and neglecting the small per locus effect of selection, each group has the same expected value of Wright's fixation index, FST = F. AT equilibrium, this is approximately 1/(1 + 4Me), where Me = 2kMf + 2(1 - k)Mm. The trait will increase when (b - c)/c greater than (1-F)/2F=2Me, where b is the expected benefit to the group and c is the expected cost of a unit change in the mean value of the altruistic trait. In particular, the group selection analogue of Hamilton's inequality, c/b less than r, where r is the coefficient of relationship, is obtained. The effect of isolation is enhanced if migration is mainly between adjacent groups and if group splitting is along family lines, as data on population structure of primates seem to indicate.
Membrane antigen on Epstein--Barr virus-infected human B cells recognized by a monoclonal antibody.
Authors: Slovin S F , Frisman D M , Tsoukas C D , Royston I , Baird S M , Wormsley S B , Carson D A , Vaughan J H
Published: May 2006

This paper describes a monoclonal antibody (B532) that detects a membrane antigen present on greater than or equal to 95% of the B cells from lines carrying the Epstein-Barr virus (EBV) genome. Evidence suggesting that B532 is EBV-related was originally obtained by using a cell-binding radioassay with different cell line substrates. Immunofluorescence and cell-sorter analysis confirmed that the antigen was present in high density on all EBV-infected lymphoblastoid B-cell lines, but not on EBV-negative B-, T-, myeloid, or null cell lines. Isolated normal peripheral blood B and T lymphocytes and monocytes failed to bind B532. The monoclonal antibody did not inhibit in vitro EVB infection nor did it block the killing of EBV-infected targets by cytotoxic T lymphocytes. The cell surface antigen recognized by B532 was shown by immunoprecipitation to have a molecular weight of approximately 45,000.
Spontaneous genetic hypertension in the rat and its relationship to reduced ac cochlear potentials: implications for preservation of human hearing.
Authors: McCormick J G , Harris D T , Hartley C B , Lassiter R B
Published: May 2006

We present controlled laboratory studies of the spontaneously hypertensive rat which indicate that hypertension is an important pathophysiological risk factor in age-related hearing loss. Our results are in concert with previous retrospective clinical studies that pointed to this possibility in man. Hypertension as a risk factor for hearing loss is within the bounds of known measures of diagnosis, treatment, and even prevention, with monitoring early in life. Because hypertension is such a major public health problem in the United States, in view of our results it is possible that its treatment and early diagnosis will benefit a significant number of people who would otherwise lose their hearing with advancing age. We compared the round window ac cochlear potential-sensitivity and -intensity functions in 10 female spontaneously hypertensive rats and 10 female normotensive Wistar-Kyoto control rats. The animals were all 12 months old and weighed between 170 and 250 g. The normotensives had higher maximum cochlear potential-intensity values compared with the hypertensives: 1,000 Hz (P less than 0.005), 5,000 Hz (P less than 0.005), and 10,000 Hz (P less than 0.01). One-microvolt isopotential cochlear potentials for the low frequencies of the normotensives showed greater sensitivity than those of the hypertensives: 100 Hz (P less than 0.05), 200 Hz (P less than 0.10), 290 Hz (P less than 0.05), and 2,000 Hz (P less than 0.10). Blood pressure of the hypertensive group was significantly greater than that of the normotensive rats (P less than 0.001). The hearts and aortas of the hypertensive group were hypertrophied. Autonomic imbalance, platelet aggregation, decreased arterioles, and natriuretic hormone were discussed as possible etiologies for the measured sensory hearing loss.
Multiple gamma-crystallins of the mouse lens: fractionation of mRNAs by cDNA cloning.
Authors: Shinohara T , Robinson E A , Appella E , Piatigorsky J
Published: May 2006

cDNAs made from polyadenylylated RNAs of the mouse lens were cloned by the G.C tailing procedure in the bacterial plasmid pBR322. Four recombinant DNAs containing gamma-crystallin sequences were identified by hybrid selection and translation. Sequence analysis of the in vivo-labeled gamma-crystallin polypeptides that cofocused isoelectrically with the hybrid-selected translation products established that the four cloned cDNAs were derived from mRNAs encoding gamma-crystallin polypeptides with similar NH2 termini. The cDNA clones had different restriction maps and could discriminate among the different gamma-crystallin mRNAs under stringent hybridization conditions. Under relaxed hybridization conditions, the cDNA clones cross-hybridized with all gamma-crystallin mRNAs, and even slightly with beta-crystallin mRNAs, as judged by in vitro translation. RNA blot hybridization showed that the mouse lens gamma-crystallin mRNAs are 840 +/- 100 nucleotides long. These data indicate that there are at least four similar gamma-crystallin mRNAs and suggest (but do not establish) the existence of a closely related family of gamma-crystallin genes.
Biosynthesis of rat insulins I and II: evidence for differential expression of the two genes.
Authors: Kakita K , Giddings S , Permutt M A
Published: May 2006

The purpose of these experiments was to determine the relative content and biosynthetic rate of insulins I and II under various experimental conditions. The two insulins were quantitated by polyacrylamide gel electrophoresis, electrotransfer to nitrocellulose paper, photoaffinity crosslinking, and immunodetection with anti-insulin antibody and 125I-labeled protein A. The ratio (mean +/- SEM) of insulins, I/II, was 1.2 +/- 0.2 in Wistar-Furth rats fasted for 4 days, 1.6 +/- 0.2 in normal rats, and 5.5 +/- 0.8 in growth hormone-tumor-bearing hyperinsulinemic rats (P less than 0.01). The increase in content of rat insulin I compared to II in the growth hormone-tumor-bearing animals was confirmed by radioimmunoassay of gel slices. To determine whether the difference in contents of rat insulins I and II in the hyperinsulinemic rats was due to increased biosynthesis or a different turnover rate, isolated rat islets were incubated in [3H]leucine for 4 hr with 5.5 mM or 16.0 mM glucose in the incubation medium. Glucose stimulated insulin biosynthesis greater than 8-fold. The ratio of synthesis of rat insulin I relative to II was 0.9 +/- 0.1 at 5.5 mM glucose and 9.8 +/- 3.3 (P less than 0.01) at 16.0 mM glucose. Therefore, under conditions that stimulate insulin biosynthesis, there was a marked preferential synthesis of rat insulin I relative to II. These studies suggest that the two rat insulin genes are expressed independently and that, under stimulatory conditions, there is preferential expression of the rat insulin I gene.
Simple model for the chemical potential change of a transported ion in active transport.
Authors: Tanford C
Published: May 2006

The mechanism for active transport of ions across a membrane probably involves two distinct conformational states of the transport protein, in which the binding sites for the transported ion face opposite sides of the membrane. It is likely that the binding affinity for the ion changes in synchrony with the change in site orientation, such that the affinity is high on the uptake side of the membrane and low on the discharge side. A structural model is proposed for the transmembrane portion of such a protein, based on the known multihelical structure of bacteriorhodopsin. This structure is well adapted to a cyclical alternation between two conformations that differ simultaneously in orientation and binding affinity. No unfolding of the helices or other significant alterations in secondary structure is required. The model is explicitly intended as a hypothetical representation of the E1 and E2 states of ATP-driven Na+,K+ and Ca2+ pumps.
Induction of androgen receptor formation by epithelium-mesenchyme interaction in embryonic mouse mammary gland.
Authors: Heuberger B , Fitzka I , Wasner G , Kratochwil K
Published: May 2006

The role of tissue interaction in the development of hormone responsiveness was studied in the embryonic mammary gland of the mouse, which becomes sensitive to testosterone on day 14. Previously, the mesenchyme had been identified as the sole target tissue for the hormone, although it was also demonstrated that its response to testosterone required the presence of mammary epithelium. Using autoradiography, we now show that [3H]testosterone or [3H]5 alpha-dihydrotestosterone is bound only by those mesenchymal cells closest to the epithelial mammary bud. When mammary epithelia were experimentally associated with mesenchyme of the mammary region and cultured together for 3 days in vitro, they also became surrounded by several layers of [3H]testosterone-binding mesenchymal cells. Correspondingly, this tissue association was accompanied by a substantial increase of androgen-binding sites in the explants. No hormone-building mesenchymal cells were seen in combinations with epidermis or pancreas epithelium; only salivary epithelium showed a weak positive effect. From these results we conclude that mammary epithelium induces the formation of androgen receptors in adjacent mesenchyme and thereby controls the development of androgen responsiveness in this tissue.
Identification of a fourth class of proteins linked to the murine major histocompatibility complex.
Authors: Monaco J J , McDevitt H O
Published: May 2006

A series of proteins biochemically and genetically distinct from previously defined murine major histocompatibility complex class I and class II antigens is precipitated by a congeneic anti-H-2d antiserum. Sixteen such proteins have been defined, exhibiting a range of molecular weights (approximately 15,000-30,000) and isoelectric points (pI approximately 4-9). These proteins are not glycosylated, and they are probably not expressed at the cell surface. They are expressed most strongly in normal macrophages and macrophage cell lines and are also found in fibroblasts, B, T, and null cell lines. The genes controlling the expression of these proteins have been tentatively mapped within the H-2 complex, between the K and I-A subregions. Three alleles have been defined: mice of the H-2 haplotypes b and q possess a "null" allele, i.e., do not express any demonstrable protein product. Mice of the d haplotype cane be distinguished by their two-dimensional gel pattern from mice of all other positive H-2 types tested thus far (a, k, f, s, and ja).
5 alpha-Cholest-8(14)-en-3 beta-ol-15-one, a potent inhibitor of sterol biosynthesis, lowers serum cholesterol and alters distributions of cholesterol in lipoproteins in baboons.
Authors: Schroepfer G J , Parish E J , Kisic A , Jackson E M , Farley C M , Mott G E
Published: May 2006

5 alpha-Cholest-8(14)-en-3 beta-0l-15-one has been found to have significant hypocholesterolemic action on oral administration to baboons at dosages of 50 and 75 mg/kg of body weight. The 15-ketosterol decreased the levels of total serum cholesterol and low density lipoprotein plus very low density lipoprotein (LDL/VLDL) cholesterol and the percentage of total cholesterol associated with LDL/VLDL and increased the percentage of total cholesterol associated with high density lipoprotein (HDL). Moreover, administration of the steroid was associated with an absolute increase in the concentration of HDL cholesterol in those animals with low HDL levels (or with a low percentage of total serum cholesterol in the HDL fraction.
Detection of unique antigenic determinants on human plasma low density lipoprotein and on delipidated apolipoprotein B.
Authors: Watt T S , Watt R M
Published: May 2006

To obtain detailed information on the role played by apolipoprotein B (apo B) in determining the structural and functional properties of human plasma low density lipoprotein, we have initiated immunochemical studies of the polypeptide. We report here the establishment of six hybridoma lines that secrete monoclonal antibodies to low density lipoprotein. In addition to recognizing antigenic determinants on low density lipoprotein, all six monoclonal antibodies react with epitope(s) on very low density, but not high density, lipoproteins. The immunoreactivity of these antibodies with low density lipoprotein and with detergent-delipidated apo B was compared in an enzyme-linked immunosorbent assay. Although all six of the antibodies reacted with the apoprotein when it was prepared in a nonionic detergent known to maintain the secondary structure of the protein, three of the six antibodies showed partial or total loss of activity with NaDodSO4- delipidated apo B. The specificity of these antibodies was tested by the ability of affinity-purified biotinylated antibodies to compete with unlabeled antibodies for antigenic sites on low density lipoprotein in a competition enzyme-linked immunosorbent assay developed with avidin-peroxidase. This competition assay allowed us to divide the antibodies into a minimum of two groups (I and II) based on the antigenic determinants on apo B that they recognized. The epitope on apo B recognized by group II antibodies was perturbed in NaDodSO4, whereas the determinant(s) on the protein reactive with group I antibodies was unaffected.
Behavior of cells at fluid interfaces.
Authors: Giaever I , Keese C R
Published: May 2006

We have cultured the murine cell lines 3T3-L1 and SV-T2 using as a substrate the layer of denatured protein that forms at the phase boundary between culture medium and fluorocarbon fluids. The growth patterns observed on these interfaces differ from those seen on conventional solid substrates. Depending on the cell strain and the composition of the fluorocarbon fluid, cells will tend to clump into isolated aggregates or form nearly confluent cell monolayers containing "lake-like" openings. We demonstrate that these growth patterns can be attributed to the ability of cultured cells to stress and break the protein monolayer on which they grow.
Alternate model for the cooperative equilibrium binding of myosin subfragment-1-nucleotide complex to actin-troponin-tropomyosin.
Authors: Hill T L , Eisenberg E , Greene L E
Published: May 2006

In this paper we introduce an alternate model for the equilibrium binding of S-l-N (S-l, subfragment l of myosin; N, nucleotide) on the troponin-tropomyosin-actin complex, including the influence of Ca2+ on this binding. In our previous model [Hill, T. L., Eisenberg, E. & Greene, L. E. (1980) Proc. Natl. Acad. Sci. USA 77, 3186-3190], we assumed that each tropomyosin unit, including one troponin-tropomyosin molecule and seven actin sites on the actin filament, could exist in two conformational states which presumably differed in the position of the tropomyosin on the actin. The binding of S-l-N or Ca2+ to the tropomyosin unit shifted the equilibrium between the two states but did not affect the intrinsic conformation of each state. In contrast, in the present model, we assume that tropomyosin can in principle occupy a continuum of positions on the actin filament. However, in any particular circumstance (N, Ca2+, salt, temperature), the tropomyosin occupies only a single position rather than existing in a dynamic equilibrium between two positions as in our earlier model. The binding of S-l-N or Ca2+ changes the position of tropomyosin on the actin filament and the exact position that the tropomyosin occupies depends on the nucleotide bound to S-l.
Characterization of an antigenic determinant of the glycoprotein that correlates with pathogenicity of rabies virus.
Authors: Dietzschold B , Wunner W H , Wiktor T J , Lopes A D , Lafon M , Smith C L , Koprowski H
Published: May 2006

The pathogenicity of fixed rabies virus strains for adult mice depends on the presence of an antigenic determinant on the viral glycoprotein. Two virus-neutralizing monoclonal antibodies have been used to identify this determinant. All pathogenic strains of fixed rabies virus bind to these antibodies and are neutralized by them, whereas nonpathogenic strains fail to react with these monoclonal antibodies and are not neutralized by them. Antigenic variants of the rabies virus with altered glycoprotein were selected by growing virus in the presence of one monoclonal antibody, 194-2. All variants that lost their ability to react with this antibody and an additional antibody, 248-8, were found to be nonpathogenic for adult mice. Analysis of tryptic peptides of the glycoproteins of pathogenic parent virus and nonpathogenic variants and the amino acid sequence of a specific variant tryptic peptide revealed that the change in pathogenicity corresponded to an amino acid substitution at position 333 of the glycoprotein molecule. The nucleotide sequence of the nonpathogenic variant glycoprotein gene contained a base change that confirmed the single amino acid substitution in the tryptic peptide replacing arginine-333 in the parental glycoprotein. We conclude that arginine-333 is essential for the integrity of an antigenic determinant and for the ability of rabies viruses to produce lethal infection in adult mice.
A seven-base-pair deletion in an intron of the albumin gene of analbuminemic rats.
Authors: Esumi H , Takahashi Y , Sato S , Nagase S , Sugimura T
Published: May 2006

Analbuminemic rats, which genetically lack serum albumin, have a mutation affecting albumin mRNA processing. Serum albumin genes were cloned from analbuminemic and normal parental Sprague-Dawley rats. Structural analyses of the two albumin genes showed that the gene from analbuminemic rats had a seven-base-pair deletion in an intron. The deletion extended from base 5 to base 11 from the 5' end of intron HI of the albumin gene. This deletion converted the sequence, G-T-A-G-G-T, which is normally located at the 5' end of intron HI, to G-T-A-G-C-G. RNA blot hybridization of analbuminemic and normal rat liver nuclear RNA using a DNA fragment containing the intron HI as a probe showed that this intron sequence persisted in albumin mRNA precursors of analbuminemic rats.
Photoaffinity labeling of the beta-adrenergic receptor from cultured lymphoma cells with [125I]iodoazidobenzylpindolol: loss of the label with desensitization.
Authors: Rashidbaigi A , Ruoho A E , Green D A , Clark R B
Published: May 2006

The beta-adrenergic antagonist [125I]iodoazidobenzylpindolol ( [125I]IABP) specifically photolabeled two polypeptides in membrane preparations from wild-type (WT) and coupling protein-deficient cyc- cultured lymphoma cells. The molecular weights of the two polypeptides determined by sodium dodecyl sulfate/polyacrylamide gel electrophoresis were 65,000 and 55,000. They were labeled in a ratio of approximately 1:1. Pretreatment of intact WT or cyc- cells with 1.0 microM epinephrine for 15 min (desensitization) resulted in a greater loss of the 55,000 Mr polypeptide (40-60%) relative to the 65,000 Mr peptide (10-30% loss). An 18- to 24-hr pretreatment of WT cells with terbutaline (down-regulation) led to a greater than 90% reduction of the photolabeling of both polypeptides, whereas a similar pretreatment of cyc- cells resulted in no further loss of labeled receptor than that observed after only a 15-min pretreatment with epinephrine. There was no indication of a change in the electrophoretic mobility of the [125I]IABP-labeled receptors after either short- or long-term agonist pretreatment. These data provide direct evidence for heterogeneity of the beta-adrenergic receptor in lymphoma cells. The differential loss of the [125I]IABP labeling in the two polypeptides suggests a functional heterogeneity as well.
Gene and protein sequences of adenovirus protein VII, a hybrid basic chromosomal protein.
Authors: Sung M T , Cao T M , Coleman R T , Budelier K A
Published: May 2006

The sequences of both the gene and the corresponding protein of adenovirus major core protein VII have been determined. The precise location of this gene is between 43.37 and 44.90 map coordinates on the viral genome. Protein VII is 173 residues long and has a molecular weight of 19,258. Detailed analysis of its sequence has revealed four basic domains separated by several predicted alpha helices. It is proposed that intrachain folding of protein VII is driven by hydrophobic interactions of the alpha helices, leaving the basic domains of the protein to interact with DNA phosphates. Protein monomers may further associate with each other in the formation of hexameric nucleosome-like particles. The displacement and replacement of protein VII during the viral infectious cycle in the host cell appears to mimic the biology of nucleoprotamine during the processes of spermatogenesis and fertilization. The presence of a protamine-like domain affirms a hybrid histone/protamine molecular structure for protein VII, although it may resemble the protamine in function.
Regulation of human fibroblast growth rate by both noncycling cell fraction transition probability is shown by growth in 5-bromodeoxyuridine followed by Hoechst 33258 flow cytometry.
Authors: Rabinovitch P S
Published: May 2006

Growth of human diploid fibroblasts in the presence of 5-bromodeoxyuridine, followed by flow cytometric analysis of DNA-specific fluorescence with Hoechst 33258 dye, allows quantitation of the proportion of cells that have not cycled, as well as those in G1 and G2 of two subsequent cell cycles. This technique allows rapid and accurate quantitation of the growth fraction and G1/S transition rate of these cells. The cell cycle kinetics of human diploid fibroblasts at all population doubling levels reveal two components: cycling cells showing a probabilistic rate of G1/S transition, and a variable proportion of noncycling cells. Both the transition probability (rate of exit from G1) and the noncycling proportion of cells change systematically as a function of serum concentration and as a function of population doubling level. The data suggest the existence of an underlying heterogeneity in the population of human diploid fibroblasts with respect to the capacity to divide in the presence of a given concentration of mitogen. Models of cell cycle kinetics must be modified to include regulation of growth by changes in the fraction of cycling cells, as well as by changes in the rate of exit from G1.
Multiple origins of life.
Authors: Raup D M , Valentine J W
Published: May 2006

There is some indication that life may have originated readily under primitive earth conditions. If there were multiple origins of life, the result could have been a polyphyletic biota today. Using simple stochastic models for diversification and extinction, we conclude: (i) the probability of survival of life is low unless there are multiple origins, and (ii) given survival of life and given as many as 10 independent origins of life, the odds are that all but one would have gone extinct, yielding the monophyletic biota we have now. The fact of the survival of our particular form of life does not imply that it was unique or superior.
Functional clonal deletion of cytotoxic T-lymphocyte precursors in chimeric thymus produced in vitro from embryonic Anlagen.
Authors: Good M F , Pyke K W , Nossal G J
Published: May 2006

Chimeric thymus, formed by fusing the prelymphoid third pharyngeal pouches of fetal mice with fetal liver, have been allowed to develop entirely in vitro. Syngeneic and allogeneic chimeras were prepared and both types of thymus were shown to contain substantial numbers of functional cytotoxic T lymphocyte precursors reactive against "third party" alloantigens. However, alloreactivity specific for H-2 antigens present on either the third pharyngeal pouch or the fetal liver was minimal. In three different allogeneic chimeric thymuses, the frequencies of cytotoxic T lymphocyte precursors reactive to H-2 antigens present on the third pharyngeal pouches were reduced to 1%, 4%, and 0% of control values, whereas, in the one allogeneic chimera tested for alloreactivity to H-2 antigens present on the fetal liver, the cytotoxic T lymphocyte precursor frequency was reduced to less than 1% of control values. The phenotype of the H-2 tolerance is shown to be one of functional clonal deletion of the cytotoxic T lymphocyte precursor.
Regulation of rat urinary and renal kallikrein and prekallikrein by corticosteroids.
Authors: Noda Y , Yamada K , Igic R , Erdös E G
Published: May 2006

Rats were adrenalectomized and injected for 7 days with dexamethasone (DEX) or deoxycorticosterone. Kallikrein and prekallikrein were assayed in urine and in a basolateral membrane-enriched fraction. The activities of renin and phospholipase A2 were also determined in the fraction. Adrenalectomy significantly decreased active kallikrein in urine. Administration of deoxycorticosterone raised the level of active kallikrein in urine without affecting the concentration of prekallikrein. Rats treated with DEX only had high Na+ and low active kallikrein excretion. The total kallikrein level (active kallikrein together with prekallikrein), however, returned to normal because DEX elevated the prekallikrein level. DEX also increased the prekallikrein concentration in the membrane-enriched fraction. Renin activity in the membrane-enriched fraction was enhanced by adrenalectomy but suppressed by either corticosteroid. The changes in the concentration of plasma renin were qualitatively similar but quantitatively different. The activity of phospholipase A2 in the membrane-enriched fraction was enhanced only by deoxycorticosterone. Thus, both gluco- and mineralocorticoids increased kallikrein excretion in the adrenalectomized animals, but DEX was apparently effective at a lower dose than deoxycorticosterone. DEX increases the prekallikrein concentration in urine and on the basal membrane of distal tubular cells and, in addition, may prevent its conversion by releasing an inhibitor of a prekallikrein activator.
Multielectron storage and hydrogen generation with colloidal semiconductors
Authors: Grätzel Michael , Moser Jacques
Published: May 2006

Multielectron storage and hydrogen generation by light is achieved in aqueous dispersions of ultrafine TiO
2
particles (120-Å diameter) when the amphiphilic viologen derivative
N
-tetradecyl-
N
′-methyl-4,4′-dipyridinium dichloride (C
14
MV
2+
) is used as an electron relay. Consecutive reduction of C
14
MV
2+
to the radical ion (C
14
MV
+
) and neutral (C
14
MV
0
) was observed after band-gap excitation of the semiconductor particle. Through surface adsorption of the relay, these electron-transfer reactions can occur very rapidly and are completed within less than 100 μsec (pH 11). Two-electron reduction of C
14
MV
2+
can be coupled with H
2
generation in alkaline medium in the presence of Pt catalyst codeposited onto the TiO
2
particle. Electron-relay-free systems are 1/15th as efficient in producing H
2
at the same pH.
Olfactory receptors in the melon fly
Dacus cucurbitae
and the oriental fruit fly
Dacus dorsalis
Authors: Metcalf Robert L. , Mitchell Wallace C. , Metcalf Esther R.
Published: May 2006

Male melon flies (
Dacus cucurbitae
) from a colony in Hawaii were evaluated for limit of response to the olfactory stimulant raspberry ketone and to more than 40 related molecules. The results were compared with the limits of response of oriental fruit flies (
Dacus dorsalis
) under identical conditions. The nature of the response of the two species to attractive compounds appeared to be identical with regard to orientation, searching, pulsating mouthparts, and compulsive feeding. However, there was very little overlap in the response of the two species to phenylpropanoid-type compounds.
D. cucurbitae
responded most strongly to
p
-hydroxyphenylpropanoids while
D. dorsalis
responded most strongly to 3,4-dimethoxyphenylpropanoids. The results are discussed in terms of antennal receptor site geometry and with regard to the coevolution of two major groups of Dacini with plant kairomones.
Consistent association between sigma elements and tRNA genes in yeast.
Authors: Brodeur G M , Sandmeyer S B , Olson M V
Published: May 2006

Sigma is a recently described family of transposable elements in yeast (Saccharomyces cerevisiae). The most striking feature of the seven sigma elements that have been previously identified is that all are located 16-18 base pairs upstream from tRNA-encoding regions. Because these cases were all encountered in the process of studying specific tRNA genes, the full extent of the association between sigma elements and tRNA genes could not be assessed. In this paper, we report a more global characterization of the sigma family in a typical laboratory yeast strain: of the 30 copies of sigma that we estimate to be present in the haploid genome, we have cloned and analyzed 25 loci. Although in two cases a pair of sigma elements were found within several kilobases of each other, the majority occur as individual elements at widely dispersed sites. Moreover, in all 25 cases analyzed, the sigma elements are closely associated with tRNA genes. Thus, the sigma transposable element has been shown to have an absolute association with another gene family.