bluuebunny/crossref_metadata_2025 huggingface dataset:
Spatial pattern of cdc2 expression in relation to meristem activity and cell proliferation during plant development.
Authors: Martinez M C , Jørgensen J E , Lawton M A , Lamb C J , Doerner P W
Published: May 2006

The p34 protein kinase encoded by the cdc2 gene is a key component of the eukaryotic cell cycle required for the G1- to S-phase transition and entry into mitosis. To study the regulation of plant meristem activity and cell proliferation, we have examined the tissue-specific accumulation of cdc2 transcripts in Arabidopsis thaliana and the related crucifer radish (Raphanus sativus) by in situ hybridization using A. thaliana cdc2 cDNA sequences as a probe. cdc2 transcripts accumulated in leaf primordia and within the vegetative shoot apical meristem. During flower development, high levels of expression were observed in meristems, in the basal regions of developing organs, in the developing vasculature, and associated with rib meristems elaborated late in the development of some floral organs. In root tips, cdc2 transcripts accumulated in the meristematic region and adjacent daughter cells but were not detected in the quiescent center. There was strong hybridization throughout the pericycle, and a further localized accumulation of cdc2 transcripts was observed in the initial stages of the activation of a new meristem at sites of lateral root development. We conclude that cdc2 expression is a critical factor in the regulation of meristem activity and establishment of proliferative competence.
A carboxyl-terminal-domain kinase associated with RNA polymerase II transcription factor delta from rat liver.
Authors: Serizawa H , Conaway R C , Conaway J W
Published: May 2006

We previously purified RNA polymerase II transcription factor delta from rat liver and found that it has an associated DNA-dependent ATPase (dATPase) activity. In this report, we show that delta is also closely associated with a protein kinase activity that catalyzes phosphorylation of the largest subunit of RNA polymerase II. Kinase activity copurifies with transcription and DNA-dependent ATPase (dATPase) activities when delta is analyzed by anion- and cation-exchange HPLC as well as by sucrose gradient sedimentation, arguing that delta possesses all three activities. Phosphorylation of the largest subunits of both rat and yeast RNA polymerase II is stimulated by DNA, whereas phosphorylation of a synthetic peptide containing multiple copies of the carboxyl-terminal heptapeptide repeat is not. Although both ATP and GTP appear to function as phosphate donors, GTP is utilized less than 10% as well as ATP. These findings suggest that delta may exert its action in transcription at least in part through a mechanism involving phosphorylation of the largest subunit of RNA polymerase II.
Interleukin 2 stimulation of p70 S6 kinase activity is inhibited by the immunosuppressant rapamycin.
Authors: Calvo V , Crews C M , Vik T A , Bierer B E
Published: May 2006

Binding of interleukin 2 (IL-2) to its receptor generates intracellular signals, including the activation of tyrosine and serine/threonine kinases. In this study the activation of the serine/threonine-specific ribosomal protein S6 kinases in response to IL-2 was analyzed in the murine T-cell line CTLL-20, a model system of IL-2-dependent proliferation. Two major classes of S6 kinases have been characterized: the 90-kDa (rsk) family and the 70-kDa family. In response to the addition of recombinant IL-2, total S6 kinase activity was increased. This S6 kinase activity could not be immunoprecipitated by an antiserum specific for S6 kinases of the 90-kDa family, exhibited a chromatographic behavior characteristic of 70-kDa S6 kinases, and was recognized by a 70-kDa S6 kinase-specific antiserum. Thus, IL-2 binding to its receptor induces specific activation of the 70-kDa family of S6 kinases. Rapamycin, a macrolide immunosuppressant that inhibits IL-2-dependent proliferation, inhibited IL-2-stimulated 70-kDa S6 kinase activity subsequent to early increases in tyrosine kinase activity. These findings imply that the targets of rapamycin include molecules involved in the activation of 70-kDa S6 kinases. These observations further suggest that S6 kinases of the 70-kDa family participate in signal transmission pathways subsequent to IL-2 binding to its receptor.
Antiparallel side-by-side dimeric motif for sequence-specific recognition in the minor groove of DNA by the designed peptide 1-methylimidazole-2-carboxamide netropsin.
Authors: Mrksich M , Wade W S , Dwyer T J , Geierstanger B H , Wemmer D E , Dervan P B
Published: May 2006

The designed peptide 1-methylimidazole-2-carboxamide netropsin (2-ImN) binds specifically to the sequence 5'-TGACT-3'. Direct evidence from NMR spectroscopy is presented that this synthetic ligand binds DNA as a 2:1 complex, which reveals that the structure is an antiparallel dimer in the minor groove of DNA. This is in contrast to the 1:1 complexes usually seen with most crescent-shaped minor groove binding molecules targeted toward A+T-rich tracts but reminiscent of a dimeric motif found for distamycin at high concentrations. These results suggest that sequence-dependent groove width may play an important role in allowing an expanded set of DNA binding motifs for synthetic peptides.
S-nitrosylation of tissue-type plasminogen activator confers vasodilatory and antiplatelet properties on the enzyme.
Authors: Stamler J S , Simon D I , Jaraki O , Osborne J A , Francis S , Mullins M , Singel D , Loscalzo J
Published: May 2006

Tissue-type plasminogen activator (t-PA) reacts upon exposure to endothelium-derived relaxing factor (EDRF) by way of the enzyme's single free sulfhydryl (Cys-83) to form a stable S-nitrosothiol protein adduct. S-nitrosylation endows t-PA with potent vasodilatory and antiplatelet properties that are accompanied by elevations in intracellular cyclic GMP analogous to those induced by low molecular weight (e.g., S-nitroso amino acid) S-nitrosothiols. Moreover, this chemical modification does not adversely affect the catalytic efficiency of t-PA, the fibrin stimulation of this activity, the binding of t-PA to fibrinogen, or the interaction of the enzyme with its physiologic serine protease inhibitor, plasminogen-activator inhibitor type I. The coupling of vasodilatory, antiplatelet, and fibrinolytic properties in one molecule makes the S-nitrosylated t-PA a unique molecular species and may provide insight into the mechanisms by which the endothelium maintains vessel patency. These data also suggest a pharmacologic approach to treatment of thromboocclusive disorders.
Mutants of complement component C3 cleaved by the C4-specific C1-s protease.
Authors: Mathias P , Carrillo C J , Zepf N E , Cooper N R , Ogata R T
Published: May 2006

To identify some of the structural features determining specific protease recognition of complement components C3 and C4, we used site-specific mutagenesis to construct mutants of murine C3 that are cleaved by the C4-specific C1-s protease. Insertion of three amino acid residues corresponding to residues at the C1-s cleavage site of human C4 into murine C3 at the analogous C3 convertase cleavage site was adequate to render the mutant protein susceptible to C1-s cleavage. In addition, insertion of C3-specific residues at the same site or introduction of the C4-specific residues as substitutions rather than as an insertion also rendered the site susceptible to cleavage, but with 10- to 50-fold lower efficiencies, and insertion of even a single amino acid residue affected recognition by C1-s. Finally, insertion of amino acid residues into mC3 partially inhibited cleavage by the alternative-pathway C3 convertase, with insertion of C3- or C4-specific residues giving about the same level of inhibition. A simple interpretation of these data is that C1-s cleavage is dependent primarily on steric accessibility and on recognition of specific amino acid residues at the cleavage site, whereas C3 convertase cleavage is dependent primarily on specific interactions distal to the cleavage site, with only relatively weak, non-C3-specific interactions at the cleavage site itself.
Brain vascular endothelial cells express JC virus large tumor antigen in immunocompetent and cyclophosphamide-treated hamsters.
Authors: Ressetar H G , Webster H D , Stoner G L
Published: May 2006

When injected intracerebrally into newborn hamsters, the human polyomavirus JC virus (JCV) establishes a nonproductive infection resulting in brain tumor formation. Using immunostaining methods to detect the JCV regulatory protein, large tumor antigen (T antigen), we have now demonstrated JCV infection of brain vascular endothelial cells (EC) in infected hamsters. JCV T antigen was detected in lectin-labeled EC as well as in von Willebrand factor-expressing EC in both cyclophosphamide-treated and nonimmunosuppressed hamster brains 16, 21, and 31 days after birth. Cyclophosphamide-treated hamsters exhibited a greater number of JCV-infected EC, whereas T-antigen expression in nonvascular cells was not affected. The influence of cyclophosphamide was most pronounced in the cerebellum where increased numbers of JCV-infected EC were located predominantly at the internal granular layer-white matter junction, also a prominent location for T-antigen-expressing neoplastic foci. The hamster model demonstrates in vivo infection of EC by a human polyomavirus and directs interest toward the role of these cells in human JCV infection.
Specific complex formation between proteins encoded by the yeast DNA repair and recombination genes RAD1 and RAD10.
Authors: Bailly V , Sommers C H , Sung P , Prakash L , Prakash S
Published: May 2006

The RAD1 and RAD10 genes of Saccharomyces cerevisiae are required for excision repair of ultraviolet light-damaged DNA, and they also function in a mitotic recombination pathway that is distinct from the double-strand-break recombination pathway controlled by RAD52. Here, we show that the RAD1 and RAD10 proteins are complexed with each other in vivo. Immunoprecipitation of yeast cell extracts with either anti-RAD1 antibody or anti-RAD10 antibody coprecipitated quantitative amounts of both RAD1 and RAD10 proteins. The level of coprecipitable RAD1 and RAD10 increased when both proteins were overproduced together, but not if only one of the proteins was overproduced. The RAD1/RAD10 complex is highly stable, being refractory to 1 M NaCl and to low concentrations of SDS. By hydroxylamine mutagenesis, we have identified a rad1 mutant allele whose encoded protein fails to complex with RAD10. The interaction-defective rad1 mutant resembles the rad1 or rad10 null mutant in defective DNA repair and recombination, implying that complex formation is essential for the expression of biological activities controlled by RAD1 and RAD10.
Induction of antigen-specific class I-restricted cytotoxic T cells by soluble proteins in vivo.
Authors: Raychaudhuri S , Tonks M , Carbone F , Ryskamp T , Morrow W J , Hanna N
Published: May 2006

Cytotoxic T lymphocytes (CTL) are induced specifically against viral and tumor antigens presented by major histocompatibility complex class I molecules on the surface of infected or transformed cells. Intracellular synthesized antigens are processed and associated with class I antigens within cells before presentation on the cell surface. Because of this special requirement for CTL induction, exogenous soluble antigens do not, in general, induce specific CTL responses. To overcome this problem, various laboratories have resorted to the use of vaccinia virus and other replicating expression vectors for intracellular antigen delivery leading to the stimulation of humoral and cell-mediated immunity to specific proteins. However, for human use it is safer to use purified and defined antigens for inducing immune responses. Using soluble ovalbumin and human immunodeficiency virus glycoprotein gp120, we have explored the possibility of using an antigen formulation consisting of squalane and Tween 80 to elicit antigen-specific CTL responses in mice. We have demonstrated that this antigen formulation is a potent inducer of CD8+, class I-restricted, antigen-specific CTLs. The CTL priming induced by soluble antigen in squalane/Tween 80 resembles the reported response to the vaccinia recombinant containing human immunodeficiency virus envelope protein and by splenocytes cytoplasmically loaded with soluble ovalbumin. The ramifications of these findings for vaccine development are discussed.
Tetrapeptide inhibitors of protein farnesyltransferase: amino-terminal substitution in phenylalanine-containing tetrapeptides restores farnesylation.
Authors: Brown M S , Goldstein J L , Paris K J , Burnier J P , Marsters J C
Published: May 2006

Protein farnesyltransferase from rat brain transfers farnesyl residues to cysteine residues in tetrapeptides that conform to the sequence CA1A2X, where C is cysteine, A1 and A2 are aliphatic amino acids, and X is methionine or serine. When the A2 residue is aromatic [e.g., phenylalanine as in Cys-Val-Phe-Met (CVFM)], the tetrapeptide continues to bind to the enzyme, but it can no longer accept a farnesyl group, and it becomes a pure inhibitor. The current studies show that this resistance to farnesylation also requires a positive charge on the cysteine amino group. Derivatization of this group with acetyl, octanoyl, or cholic acid residues or extension of the peptide with an additional amino acid restores the ability of phenylalanine-containing peptides to accept a farnesyl residue. The same result was obtained when the amino group of cysteine was deleted (mercaptopropionyl-VFM). These data suggest that the positive change on the cysteine amino group acts in concert with an aromatic residue in the A2 position to render peptides resistant to farnesylation by the rat brain enzyme.
Either of two functionally redundant sensor proteins, NarX and NarQ, is sufficient for nitrate regulation in Escherichia coli K-12.
Authors: Rabin R S , Stewart V
Published: May 2006

Nitrate acts through the response regulator NarL to activate and repress anaerobic respiratory gene expression in Escherichia coli. The narX gene product encodes a cognate sensor (histidine protein kinase). However, previous work discovered that NarL-mediated nitrate regulation is essentially normal in delta narX deletion mutants. In other two-component regulatory systems studied, the cognate sensor gene is essential for normal regulation. We suggested that NarX-mediated signal transduction reactions are also provided by a functionally redundant nitrate sensor, NarQ. We report here the identification and analysis of narQ insertion mutants. In narX+ strains, a narQ::Tn10 insertion had no perceptible effect on nitrate regulation. However, the same narQ::Tn10 insertion eliminated nitrate regulation when present in delta narX deletion strains. Thus, either narX+ or narQ+ was sufficient for essentially normal NarL-mediated nitrate regulation. The narQ gene mapped to 53 minutes on the E. coli genetic map, a location distinct from all known nitrate regulatory or target genes. The predicted NarQ sequence shares substantial similarity with NarX, particularly in the histidine protein kinase region and in a region of shared similarity with the methyl-accepting chemotaxis proteins. Both NarQ and NarX apparently have N-terminal periplasmic domains, but the primary structures of these regions are largely dissimilar in the two sequences. Analysis of narX* and narL missense alleles in narQ+ versus narQ::Tn10 backgrounds suggests that NarQ and NarX may have subtle functional differences.
Termination of second messenger signaling in olfaction.
Authors: Boekhoff I , Breer H
Published: May 2006

By using isolated rat olfactory cilia and a fast kinetics methodology, it has been demonstrated that odorant-induced second messenger signaling in the millisecond time range is terminated via phosphorylation reactions catalyzed by specific protein kinases. The cyclic adenosine nucleotide pathway is turned off by kinase A activity, whereas the inositol trisphosphate cascade is terminated by kinase C. The data support the concept that desensitization of odorant responses involves phosphorylation of key elements in the transduction cascade.
Cloning and antisense oligodeoxynucleotide inhibition of a human homolog of cdc2 required in hematopoiesis.
Authors: Lapidot-Lifson Y , Patinkin D , Prody C A , Ehrlich G , Seidman S , Ben-Aziz R , Benseler F , Eckstein F , Zakut H , Soreq H
Published: May 2006

Mechanisms triggering the commitment of pluripotent bone marrow stem cells to differentiated lineages such as mononuclear macrophages or multinucleated megakaryocytes are still unknown, although several lines of evidence suggested correlation between cholinergic signaling and hematopoietic differentiation. We now present cloning of a cDNA coding for CHED (cholinesterase-related cell division controller), a human homolog of the Schizosaccharomyces pombe cell division cycle 2 (cdc2)-like kinases, universal controllers of the mitotic cell cycle. Library screening, RNA blot hybridization, and direct PCR amplification of cDNA reverse-transcribed from cellular mRNA revealed that CHED mRNA is expressed in multiple tissues, including bone marrow. The CHED protein includes the consensus ATP binding and phosphorylation domains characteristic of kinases, displays 34-42% identically aligned amino acid residues with other cdc2-related kinases, and is considerably longer at its amino and carboxyl termini. An antisense oligodeoxynucleotide designed to interrupt CHED's expression (AS-CHED) significantly reduced the ratio between CHED mRNA and actin mRNA within 1 hr of its addition to cultures, a reduction that persisted for 4 days. AS-CHED treatment selectively inhibited megakaryocyte development in murine bone marrow cultures but did not prevent other hematopoietic pathways, as evidenced by increasing numbers of mononuclear cells. An oligodeoxynucleotide blocking production of the acetylcholine-hydrolyzing enzyme, butyrylcholinesterase, displayed a similar inhibition of megakaryocytopoiesis. In contrast, an oligodeoxynucleotide blocking production of the human 2Hs cdc2 homolog interfered with production of the human 2Hs cdc2 homolog interfered with cellular proliferation without altering the cell-type composition of these cultures. Therefore, these findings strengthen the link between cholinergic signaling and cell division control in hematopoiesis and implicate both CHED and cholinesterases in this differentiation process.
Cloning of the alpha 1 subunit of a voltage-dependent calcium channel expressed in pancreatic beta cells.
Authors: Seino S , Chen L , Seino M , Blondel O , Takeda J , Johnson J H , Bell G I
Published: May 2006

The isoforms of the alpha 1 subunits of voltage-dependent Ca2+ channels expressed in human pancreatic islets were identified by using a pair of degenerate oligonucleotide primers and the polymerase chain reaction (PCR) to amplify mRNAs encoding alpha 1 subunit-like sequences. The sequences of the PCR products indicate that islets express the heart-type alpha 1 subunit as well as a second isoform whose complete sequence has not been previously reported. The sequences of cloned cDNAs encoding the human beta-cell, or neuroendocrine-type, alpha 1 subunit indicate that it is composed of 2181 amino acids. It shares 68%, 64%, and 41% identity with the sequences of the alpha 1 subunits of rabbit heart, skeletal muscle, and brain, respectively, and is predicted to have a similar structure including four homologous domains composed of six membrane-spanning segments each. RNA blotting studies indicate that the beta-cell-type alpha 1 subunit is also expressed in brain as well as in the insulin-producing cell lines RINm5F and beta TC-3; however, it could not be detected by RNA blotting in a third cell line, HIT-T15. In situ hybridization studies revealed expression of beta-cell-type alpha 1 subunit mRNA in beta cells of rat pancreatic islets, implying that this protein may play a role in the regulation of insulin secretion.
Identification of a 1,25-dihydroxyvitamin D3-response element in the 5'-flanking region of the rat calbindin D-9k gene.
Authors: Darwish H M , DeLuca H F
Published: May 2006

The rat calbindin D-9k gene is transcriptionally regulated by 1,25-dihydroxyvitamin D3 in the intestine. We have examined the 5'-flanking region of this gene and identified a 1,25-dihydroxyvitamin D3-responsive element (DRE) between nucleotides -489 and -445. This element confers 1,25-dihydroxyvitamin D3 responsiveness through its native promoter and the heterologous thymidine kinase promoter, and it contains the sequence GGGTGTCGGAAGCCC, which is homologous to the other previously identified DREs. Incubation of this element with the 1,25-dihydroxyvitamin D3 receptor produced a specific protein-DNA complex, which shifted to a higher molecular weight form upon the addition of a monoclonal antibody specific to the 1,25-dihydroxyvitamin D3 receptor. Therefore, the 5'-flanking region of the rat calbindin D-9k gene contains a DRE that mediates the enhanced expression of this gene by 1,25-dihydroxyvitamin D3 in the intestine.
Femtosecond spectral evolution of the excited state of bacterial reaction centers at 10 K.
Authors: Vos M H , Lambry J C , Robles S J , Youvan D C , Breton J , Martin J L
Published: May 2006

The femtosecond spectral evolution of reaction centers of Rhodobacter sphaeroides R-26 was studied at 10 K. Transient spectra in the near infrared region, obtained with 45-fs pulses (pump pulses centered at 870 nm and continuum probe pulses), were analyzed with associated kinetics at specific wavelengths. The t = 0-fs transient spectrum is very rich in structure; it contains separate induced bands at 807 and 796 nm and a bleaching near 760 nm, reflecting strong changes in interaction between all pigments upon formation of the excited state. A complex spectral evolution in the 800-nm region, most notably the bleaching of the 796-nm band, takes place within a few hundred femtosecond--i.e., on a time scale much faster than electron transfer from the primary donor P to the bacteriopheophytin acceptor HL. The remarkable initial spectral features and their evolution are presumably related to the presence of HL, as they were not observed in the DLL mutant of Rhodobacter capsulatus, which lacks this pigment. A simple linear reaction scheme with an intermediate state cannot account for our data; the initial spectral evolution must reflect relaxation processes within the excited state. The importance for primary photochemistry of long distance interactions in the reaction center is discussed.
Mutations in the Jun delta region suggest an inverse correlation between transformation and transcriptional activation.
Authors: Håvarstein L S , Morgan I M , Wong W Y , Vogt P K
Published: May 2006

The viral Jun protein (v-Jun) transforms chicken embryo fibroblasts (CEF) more effectively than its cellular counterpart (c-Jun). In certain cell types v-Jun is also a stronger transcriptional activator than c-Jun. These functional differences between v-Jun and c-Jun result from a deletion in v-Jun (referred to as "delta deletion") that seems to weaken the interaction of Jun with a negative cellular regulator molecule. These observations suggested that the oncogenicity of v-Jun may be due to an enhanced ability to activate transcription of target genes. To test this hypothesis, we constructed several deletions in the delta domain of chicken c-Jun and determined their transforming and transactivating properties. Surprisingly, we found an inverse correlation between the ability of the mutants to transform CEF and to transactivate the collagenase and transin promoters in CEF. In contrast, there was no significant effect of the delta mutations in c-Jun on transactivation in F9 murine embryonal carcinoma cells. The function of the delta region is therefore cell-type specific. The inverse correlation between transformation and transactivation in CEF suggests that the strong growth-promoting effect of v-Jun may be related to a failure to activate the transcription of growth attenuating genes.
Vaccinia virus complement-control protein prevents antibody-dependent complement-enhanced neutralization of infectivity and contributes to virulence.
Authors: Isaacs S N , Kotwal G J , Moss B
Published: May 2006

The role of a viral gene product in evasion of the host immune response was investigated. The antibody-dependent complement-enhanced neutralization of vaccinia virus infectivity was prevented by the culture medium from vaccinia virus-infected cells. The vaccinia virus complement-control protein (VCP) was identified as the secreted product of vaccinia virus gene C21L and has homology to a group of eukaryotic genes encoding regulators of complement activation. Thus, the culture medium from cells infected with a C21L deletion mutant was VCP deficient and had little or no effect on antibody-dependent complement-enhanced neutralization. In addition, the anticomplement effect was associated with the C21L-encoded protein partially purified from the medium of cells infected with wild-type virus. Antibody-dependent, complement-enhanced neutralization of vaccinia virus occurred with a complement source that was deficient in the classical pathway complement component C4 and required the alternative pathway complement factor B. Furthermore, the presence of VCP abrogated the complement-enhanced neutralization in C4-deficient serum. Together with previous hemolysis data, the present result suggests that VCP can inhibit both the classical and alternative pathways of complement activation. Skin lesions caused by the C21L deletion mutant were smaller than those caused by wild-type virus, demonstrating an important role for VCP in virulence. The C21L deletion mutant also was attenuated in C4-deficient guinea pigs, consistent with in vitro studies. Vaccinia virus appears to have acquired the ability to regulate the complement cascade for the purpose of evading the host immune response.
Expression and crystallization of a soluble and functional form of an Fc receptor related to class I histocompatibility molecules.
Authors: Gastinel L N , Simister N E , Bjorkman P J
Published: May 2006

Maternal transport of immunoglobulin to the newborn mammal is important for immune defense during the first weeks of independent life. Receptors for the Fc portion of IgG mediate the transfer of immunoglobulin from milk to the bloodstream of newborn mice and rats, by passage through intestinal epithelial cells. Neonatal Fc receptors (FcRn) isolated from intestinal epithelial cells of suckling rats bear a striking resemblance to class I histocompatibility molecules. The heavy chain of FcRn has sequence similarity in three extracellular domains to the corresponding domains of class I molecules, and the light chain of both types of molecules is beta 2-microglobulin. To facilitate biochemical characterization and crystallization of FcRn, we have expressed a secreted form, as well as two different lipid-linked forms solubilizable by phospholipase treatment. The lipid-linked forms are heterodimers consisting of beta 2-microglobulin and the extracellular portion of the heavy chain and are anchored to the membrane by a phosphatidylinositol linkage attached to either the heavy chain or beta 2-microglobulin. Cells expressing either lipid-linked form bind rat Fc, reproducing the known physiological pH dependence of binding. Secreted FcRn has been purified in yields up to 40 mg/liter from cell supernatants. Circular dichroism spectra of soluble FcRn appear similar to spectra of class I MHC molecules, suggesting that the similarities in primary sequence extend also to a similarity in secondary structure. Soluble FcRn crystallizes in a form amenable to a structure determination by x-ray diffraction methods, which will ultimately allow a detailed comparison of the two types of molecules.
Most gamma delta T cells develop normally in beta 2-microglobulin-deficient mice.
Authors: Correa I , Bix M , Liao N S , Zijlstra M , Jaenisch R , Raulet D
Published: May 2006

The specificity of T cells bearing gamma delta T-cell receptors (gamma delta+ T cells) is poorly characterized. Earlier studies suggest that like alpha beta+CD8+ T cells, some gamma delta+ T cells may recognize antigens associated with class I major histocompatibility complex molecules. alpha beta+CD8+ T cells are nearly absent in class I-deficient mice (mutant for beta 2-microglobulin), reflecting a requirement for intrathymic "positive selection" of these cells by class I molecules. Here, we examine whether the development of gamma delta+ T cells is altered in the beta 2-microglobulin mutant mice. We show that the cellularity, marker expression, repertoire, and functional competence of gamma delta+ T cells are not detectably deficient in beta 2-microglobulin mutant mice. We conclude that class I expression is unnecessary for the development of most gamma delta+ T cells.
Engineering of glucose-stimulated insulin secretion and biosynthesis in non-islet cells.
Authors: Hughes S D , Johnson J H , Quaade C , Newgard C B
Published: May 2006

The high-capacity glucose transporter known as GLUT-2 and the glucose phosphorylating enzyme glucokinase are thought to be key components of the "glucose-sensing apparatus" that regulates insulin release from the beta cells of the islets of Langerhans in response to changes in external glucose concentration. AtT-20ins cells are derived from anterior pituitary cells and are like beta cells in that they express glucokinase and have been engineered to secrete correctly processed insulin in response to analogs of cAMP, but, unlike beta cells, they fail to respond to glucose and lack GLUT-2 expression. Herein we demonstrate that stable transfection of AtT-20ins cells with the GLUT-2 cDNA confers glucose-stimulated insulin secretion and glucose regulation of insulin biosynthesis and also results in glucose potentiation of the secretory response to non-glucose secretagogues. This work represents a first step toward creation of a genetically engineered "artificial beta cell."
A DNA polymerase alpha pause site is a hot spot for nucleotide misinsertion.
Authors: Fry M , Loeb L A
Published: May 2006

In this study we examined whether the arrest of DNA polymerase alpha (pol alpha)-catalyzed DNA synthesis at template pause sites entails terminal nucleotide misincorporation. An approach was developed to identify the 3'-terminal nucleotide in nascent DNA chains that accumulate at pause sites. A radioactive 5'-end-labeled primer was annealed to a bacteriophage M13mp2 single-stranded DNA template and elongated by pol alpha. Individual DNA chains that were accumulated at pause sites were resolved by sequencing gel electrophoresis, isolated, and purified. These DNA chains were elongated by pol alpha by using four annealed synthetic DNA templates, each of which contained a different nucleotide at the position opposite the 3' terminus of the arrested chain. Owing to the high preference of pol alpha for matched-over-mismatched primer termini, only those templates that contain a nucleotide that is complementary to the 3' terminus of the isolated pause-site chain are copied. Electrophoresis of product DNA showed the extent of copying of each template and thus identified the 3'-terminal nucleotide of the pause-site chains. We found that product DNA chains terminate with a noncomplementary 3'-terminal nucleotide opposite pause sites within the sequence 3'-d(AAAA)-5' at positions 6272-6269 of the M13mp2 genome. pol alpha catalyzed misincorporation of dG or dA into the 3' terminus of nascent chains opposite two of the M13mp2 template dA residues. A similar analysis of a different pause site did not reveal significant misincorporation opposite template dC. These results suggest that some but not all sites at which pol alpha pauses may constitute loci of mutagenesis.
Peptoids: a modular approach to drug discovery.
Authors: Simon R J , Kania R S , Zuckermann R N , Huebner V D , Jewell D A , Banville S , Ng S , Wang L , Rosenberg S , Marlowe C K
Published: May 2006

Peptoids, oligomers of N-substituted glycines, are described as a motif for the generation of chemically diverse libraries of novel molecules. Ramachandran-type plots were calculated and indicate a greater diversity of conformational states available for peptoids than for peptides. The monomers incorporate t-butyl-based side-chain and 9-fluorenylmethoxy-carbonyl alpha-amine protection. The controlled oligomerization of the peptoid monomers was performed manually and robotically with in situ activation by either benzotriazol-1-yloxytris(pyrrolidino)phosphonium hexafluorophosphate or bromotris(pyrrolidino)phosphonium hexaflurophosphate. Other steps were identical to peptide synthesis using alpha-(9-fluorenylmethoxycarbonyl)amino acids. A total of 15 monomers and 10 oligomers (peptoids) are described. Preliminary data are presented on the stability of a representative oligopeptoid to enzymatic hydrolysis. Peptoid versions of peptide ligands of three biological systems (bovine pancreatic alpha-amylase, hepatitis A virus 3C proteinase, and human immunodeficiency virus transactivator-responsive element RNA) were found with affinities comparable to those of the corresponding peptides. The potential use of libraries of these compounds in receptor- or enzyme-based assays is discussed.
Foraging ability of rufous hummingbirds on hummingbird flowers and hawkmoth flowers.
Authors: Grant V , Temeles E J
Published: May 2006

We examine the suitability of ornithophilous flowers and sphingophilous flowers in Ipompsis and Aquilegia for nectar foraging by the hummingbird Selasphorus rufus. In S. rufus, bill length averages 18.9 mm in females and 17.3 mm in males. Maximal tongue extension approximates bill length, suggesting that birds can feed from floral tubes up to 33.5 mm in length. However, their ability to do so is limited by two factors. First, the maximal depth at which S. rufus can extract nectar decreases with the width of the floral tube. Second, feeding time is shortest in short floral tubes and progressively increases as the tubes lengthen because of increased time required for tongue extension and retraction. Hence, nectar foraging occurs with optimal efficiency in moderately broad floral tubes with lengths that do not exceed or only slightly exceed the bill length plus </=5-mm tongue extension. In most ornithophilous taxa of Ipomopsis and Aquilegia, the floral tubes have lengths and widths in the optimal range for nectar foraging by S. rufus, whereas in the sphingophilous taxa, the basal nectar either may be reached but at much higher cost or, more frequently, is beyond reach of bills and tongues. The flower-visiting habits of S. rufus and other hummingbirds in nature are generally congruent with these conclusions and support the case for coadaptation between these plants and pollinators.
Dominant negative selection of heterologous genes: isolation of Candida albicans genes that interfere with Saccharomyces cerevisiae mating factor-induced cell cycle arrest.
Authors: Whiteway M , Dignard D , Thomas D Y
Published: May 2006

We have used a genomic library of Candida albicans to transform Saccharomyces cerevisiae and screened for genes that act similarly to dominant negative mutations by interfering with pheromone-mediated cell cycle arrest. Six different plasmids were identified from 2000 transformants; four have been sequenced. One gene (CZF1) encodes a protein with structural motifs characteristic of a transcription factor. A second gene (CCN1) encodes a cyclin homologue, a third (CRL1) encodes a protein with sequence similarity to GTP-binding proteins of the RHO family, and a fourth (CEK1) encodes a putative kinase of the ERK family. Since CEK1 confers a phenotype similar to that of the structurally related S. cerevisiae gene KSS1 but cannot complement a KSS1 defect, it is evident that dominant negative selection can identify proteins that complementation screens would miss. Because dominant negative mutations exert their influence even in wild-type strain backgrounds, this approach should be a general method for the analysis of complex cellular processes in organisms not amenable to direct genetic analysis.
Three-dimensional structure of two crystal forms of FabR19.9 from a monoclonal anti-arsonate antibody.
Authors: Lascombe M B , Alzari P M , Poljak R J , Nisonoff A
Published: May 2006

The three-dimensional structure of FabR19.9 from a well-characterized anti-p-azobenzenearsonate monoclonal antibody has been determined by x-ray diffraction techniques in two crystalline forms (I and II) to a resolution of 2.8 and 2.7 A, respectively. Essentially the same tertiary and quaternary structure of the Fab is observed in the two forms. The major difference resides in the intermolecular contacts, which are interpreted to favor an irreversible transition from the metastable form I to the more stable form II. The third complementarity-determining region of the heavy chain (H3) folds back over the combining site and requires rearrangement for hapten binding. This dynamic requirement on H3 is consistent with its mobility in the structure and can explain hapten binding to an otherwise inaccessible antibody combining site.
Instability of assembled T-cell receptor complex that is associated with rapid degradation of zeta chains in immature CD4+CD8+ thymocytes.
Authors: Kosugi A , Weissman A M , Ogata M , Hamaoka T , Fujiwara H
Published: May 2006

The intracellular fate of newly synthesized T-cell receptor (TCR) chains was compared in CD4+CD8+ (double positive; DP) thymocytes and in CD4+CD8- or CD4-CD8+ (single positive; SP) thymocytes. Purified DP and SP thymocytes from normal adult mice were analyzed by pulse-chase metabolic labeling and immunoprecipitation with specific anti-TCR antibodies. Biosynthesis of invariant chains (CD3 gamma, -delta, -epsilon, and zeta) was comparable between DP and SP thymocytes, whereas DP thymocytes synthesized TCR alpha and TCR beta chains at lower and higher levels than SP thymocytes, respectively. These newly synthesized TCR chains were degraded at different rates in SP thymocytes based on their sensitivities for degradation as previously reported: TCR alpha, TCR beta, CD3 gamma, and CD3 delta chains were rapidly degraded and CD3 epsilon and zeta chains were stable. Although the degradation rates of clonotypic and invariant CD3 chains were similar in DP and SP thymocytes, the zeta subunit was rapidly degraded in DP thymocytes (t1/2, approximately 1.5 hr). Degradation of zeta was inhibited by NH4Cl, implicating lysosomes as the site of degradation. Comparison of TCR subunit assembly in DP and SP thymocytes demonstrated that, despite the same relative rate of formation of TCR complexes in a pulse period (30 min), complete complexes were unstable and degraded during the subsequent 6 hr of chase in DP thymocytes. This contrasted with the stability and a progressive increase in the levels of completely assembled complexes in SP thymocytes. Thus, these results demonstrate that a unique posttranslational regulation operates in the formation of TCR complexes in DP thymocytes and that lack of stability of complete TCR complexes is a crucial mechanism that may account for the limited surface TCR expression on this thymocyte subset.
Characterization of the genes encoding phycoerythrin in the red alga Rhodella violacea: evidence for a splitting of the rpeB gene by an intron.
Authors: Bernard C , Thomas J C , Mazel D , Mousseau A , Castets A M , Tandeau de Marsac N , Dubacq J P
Published: May 2006

The phycobilisome of the eukaryotic unicellular red alga Rhodella violacea presents in some respects an organization that is intermediate between those of the homologous counterparts found in cyanobacteria (the putative chloroplast progenitor) and more advanced, pluricellular red algae. This suggests evolutionary relationships that we investigated at the genome level. The present work describes the sequences of two rhodophytan phycobilisome genes, rpeA and rpeB. These chloroplast genes encode the alpha and beta subunits of phycoerythrin, the major component of the light-harvesting antennae and one of the most abundant cellular proteins in these algae. The amino acid sequences deduced from both rpeA and rpeB present strong homologies with those previously reported for phycoerythrin subunits of cyanobacteria, rhodophyta, and cryptomonads. The main difference with the corresponding cyanobacterial genes was the unexpected occurrence of an intervening sequence that split rpeB into two exons. This intervening sequence presents characteristics of group II introns but lacks several structural domains. Transcriptional analyses showed that the two rpe genes are cotranscribed and that the major RNA species detected corresponds to a mature mRNA lacking the intron. As the phycobiliproteins form a group of closely related polypeptides in cyanobacteria and rhodophyta, the molecular events affecting the corresponding genes, such as the rpeB intron, may be a clue to elucidate some aspects of the molecular processes involved in the evolution of plastid genes.
Reverse transcriptase of human immunodeficiency virus can use either human tRNA(3Lys) or Escherichia coli tRNA(2Gln) as a primer in an in vitro primer-utilization assay.
Authors: Kohlstaedt L A , Steitz T A
Published: May 2006

Although the reverse transcriptase (RT) of human immunodeficiency virus (HIV) uses human tRNA(3Lys) as a primer of viral genome DNA synthesis in vivo, HIV RT binds Escherichia coli glutamine tRNA and in vitro-made human lysine tRNA with nearly equivalent affinities. We show that HIV RT can use either tRNA(3Lys) or tRNA(2Gln) as a primer for DNA synthesis in vitro without the addition of any other host or viral proteins. E. coli tRNA(2Gln) can serve as a primer for HIV RT if a primer-binding site sequence complementary to the 3' end of tRNA(2Gln) is at the 3' end of the template. With this reduced template, the specificity of binding the proper tRNA is due to base-pairing between a bound tRNA to the primer-binding site of the viral RNA template rather than sequence-specific recognition of tRNA(3Lys) by RT. If an 8-nucleotide viral sequence 3' to the primer-binding site is included in the template, then addition of Zn2+ or Co2+ is required for tRNA(3Lys)-primed synthesis, and tRNA(2Gln) now fails to prime synthesis. The latter result implies that a template sequence adjacent to the primer-binding site and containing 6 nucleotides complementary to the anticodon loop of human tRNA(3Lys) plays an active role in tRNA discrimination.
Distinct binding sites on HLA-DR for invariant chain and staphylococcal enterotoxins.
Authors: Karp D R , Jenkins R N , Long E O
Published: May 2006

During biosynthesis, class II molecules of the major histocompatibility complex exist as complexes of the polymorphic alpha and beta chains in association with trimers of the invariant chain (Ii). The nonpolymorphic Ii contains sequences necessary for proper targeting of class II to endosomal compartments, where Ii is degraded. Ii also prevents the premature association of antigenic peptides with class II molecules. It is not known whether the effect of Ii on peptide binding extends to other ligands of class II, specifically exogenous superantigens. Cells expressing a mutant Ii molecule stably associated with HLA-DR at the cell surface were tested for their ability to interact with staphylococcal toxins. Most toxins (staphylococcal enterotoxins A-E and exfoliative toxin) were found to bind to cells expressing this alpha beta Ii complex with levels comparable to cells expressing only alpha beta chains at the cell surface. Cells expressing surface alpha beta Ii complexes stimulated polyclonal populations of peripheral blood T cells in association with these toxins. Binding of toxic shock syndrome toxin (TSST) and subsequent stimulation of T cells were reduced by the presence of the Ii. This reduction was not due to an alteration in the repertoire of T cells responding to TSST in the presence of Ii. Data from experiments with a T-cell clone suggest that interactions between class II molecules and T-cell antigen receptors occur during staphylococcal enterotoxin-mediated stimulation and that surface Ii does not interfere with such interactions.
Transfer and expression of the human multiple drug resistance gene into live mice.
Authors: Podda S , Ward M , Himelstein A , Richardson C , de la Flor-Weiss E , Smith L , Gottesman M , Pastan I , Bank A
Published: May 2006

The human multiple drug resistance (MDR) gene has been used as a selectable marker to increase the proportion of bone marrow cells that contain and express this gene by drug selection. By constructing retroviral vectors containing and expressing the MDR gene and a nonselectable gene such as the beta-globin gene, enrichment for cells containing both of these genes can be achieved. A retroviral construct containing MDR cDNA in a Harvey virus-based vector has been used to transfect our ecotropic 3T3 retroviral packaging line GP+E86. Clones have been isolated by exposure of the retrovirally transfected cells (MDR producer cells) to colchicine (60 ng/ml), a selective agent that kills MDR-negative cells. Flow cytometry analysis (fluorescence-activated cell sorting) with an antibody to MDR demonstrates expression of human MDR protein on the surface of these colchicine-resistant producer clones. Untransfected GP+E86 cells are negative. Colchicine-resistant clones were titered using clone supernatants and the highest titer clone (4 x 10(4) viral particles per ml) was cocultured with 10(6) donor mouse bone marrow cells for 24-48 hr. The donor cells were then injected into congenic irradiated mice, and the presence of the MDR gene was assayed by the polymerase chain reaction (PCR) analysis using MDR-specific primers. In one experiment eight of nine transduced mice were positive for MDR by PCR of peripheral blood 14 and 50 days posttransplantation; after 240 days three of nine transduced mice were positive. Bone marrow obtained from one of these positive animals was stained with the MDR monoclonal antibody and the granulocyte population was analyzed by FACS. Approximately 14% of the total granulocyte pool contain increased levels of MDR protein. In addition, the bone marrow cells of several mice initially positive for MDR gene by PCR, and subsequently negative, were exposed to taxol, a drug whose detoxification depends on MDR gene expression; a positive signal was obtained in all of these mice, indicating drug selection of MDR-positive marrow cells. Cell sorting studies of these mice also show an increased number of high-MDR-expressing marrow cells, selected after exposure to taxol. Thus, in this live animal model MDR transduction is effective in selecting a human MDR-expressing population of marrow cells resistant to taxol chemotherapy. This strategy may, thus, be useful in humans to prevent the marrow toxicity induced by anticancer agents such as taxol and as a selectable marker to enrich for cells simultaneously transduced with a nonselectable gene.