bluuebunny/crossref_metadata_2025 huggingface dataset:
Mutation rate varies among alleles at a microsatellite locus: Phylogenetic evidence
Authors: Jin Li , Macaubas Claudia , Hallmayer Joachim , Kimura Akinori , Mignot Emmanuel
Published: July 2002

The understanding of the mutational mechanism that generates high
levels of variation at microsatellite loci lags far behind the
application of these genetic markers. A phylogenetic approach was
developed to study the pattern and rate of mutations at a dinucleotide
microsatellite locus tightly linked to HLA-DQB1 (DQCAR). A random
Japanese population (
n
= 129) and a collection of
multiethnic samples (
n
= 941) were typed at the DQB1
and DQCAR loci. The phylogeny of DQB1 alleles was then reconstructed
and DQCAR alleles were superimposed onto the phylogeny. This approach
allowed us to group DQCAR alleles that share a common ancestor. The
results indicated that the DQCAR mutation rate varies drastically among
alleles within this single microsatellite locus. Some DQCAR alleles
never mutated during a long period of evolutionary time. Sequencing of
representative DQCAR alleles showed that these alleles lost their
ability to mutate because of nucleotide substitutions that shorten the
length of uninterrupted CA repeat arrays; in contrast, all mutating
alleles had relatively longer perfect CA repeat sequences.
Domains of P2X receptors involved in desensitization
Authors: Werner Pia , Seward Elizabeth P. , Buell Gary N. , North R. Alan
Published: July 2002

ATP-gated ion channels (P2X receptors) are abundantly expressed in
both neuronal and nonneuronal tissues, where they can serve as
postsynaptic receptors. The response to ATP shows marked
desensitization in some tissues but not others. Currents induced by ATP
in
Xenopus
oocytes expressing cloned P2X
1
(or P2X
3
) receptors had strong desensitization, whereas
currents in cells expressing P2X
2
receptors desensitized
relatively little (90% vs. 14% decline of current in a 10-s
application). In chimeric receptors, substitution into the
P2X
1
receptor of either one of two 34-residue segments from
the P2X
2
receptor removed the desensitization; these
segments included the first or the second hydrophobic domain. In
contrast, desensitization was introduced into the P2X
2
receptor only by providing both these segments of the P2X
1
(or P2X
3
) receptor. This suggests that desensitization
requires interaction between the two hydrophobic domains of the
receptor, and supports the view that these are membrane-spanning
segments.
Scale dependence in earthquake phenomena and its relevance to earthquake prediction.
Authors: Aki K
Published: July 2002

The recent discovery of a low-velocity, low-Q zone with a width of 50-200 m reaching to the top of the ductile part of the crust, by observations on seismic guided waves trapped in the fault zone of the Landers earthquake of 1992, and its identification with the shear zone inferred from the distribution of tension cracks observed on the surface support the existence of a characteristic scale length of the order of 100 m affecting various earthquake phenomena in southern California, as evidenced earlier by the kink in the magnitude-frequency relation at about M3, the constant corner frequency for earthquakes with M below about 3, and the sourcecontrolled fmax of 5-10 Hz for major earthquakes. The temporal correlation between coda Q-1 and the fractional rate of occurrence of earthquakes in the magnitude range 3-3.5, the geographical similarity of coda Q-1 and seismic velocity at a depth of 20 km, and the simultaneous change of coda Q-1 and conductivity at the lower crust support the hypotheses that coda Q-1 may represent the activity of creep fracture in the ductile part of the lithosphere occurring over cracks with a characteristic size of the order of 100 m. The existence of such a characteristic scale length cannot be consistent with the overall self-similarity of earthquakes unless we postulate a discrete hierarchy of such characteristic scale lengths. The discrete hierarchy of characteristic scale lengths is consistent with recently observed logarithmic periodicity in precursory seismicity.
Slip complexity in earthquake fault models.
Authors: Rice J R , Ben-Zion Y
Published: July 2002

We summarize studies of earthquake fault models that give rise to slip complexities like those in natural earthquakes. For models of smooth faults between elastically deformable continua, it is critical that the friction laws involve a characteristic distance for slip weakening or evolution of surface state. That results in a finite nucleation size, or coherent slip patch size, h*. Models of smooth faults, using numerical cell size properly small compared to h*, show periodic response or complex and apparently chaotic histories of large events but have not been found to show small event complexity like the self-similar (power law) Gutenberg-Richter frequency-size statistics. This conclusion is supported in the present paper by fully inertial elastodynamic modeling of earthquake sequences. In contrast, some models of locally heterogeneous faults with quasi-independent fault segments, represented approximately by simulations with cell size larger than h* so that the model becomes "inherently discrete," do show small event complexity of the Gutenberg-Richter type. Models based on classical friction laws without a weakening length scale or for which the numerical procedure imposes an abrupt strength drop at the onset of slip have h* = 0 and hence always fall into the inherently discrete class. We suggest that the small-event complexity that some such models show will not survive regularization of the constitutive description, by inclusion of an appropriate length scale leading to a finite h*, and a corresponding reduction of numerical grid size.
Linking topography of its potential surface with the dynamics of folding of a protein model
Authors: Berry R. Stephen , Elmaci Nuran , Rose John P. , Vekhter Benjamin
Published: July 2002

The “3-color, 46-bead” model of a folding polypeptide is the vehicle for adapting to proteins a mode of analysis used heretofore for atomic clusters, to relate the topography of the potential surface to the dynamics that lead to formation of selected structures. The analysis is based on sequences of stationary points—successive minima, joined by saddles—that rise monotonically in energy from basin bottoms. Like structure-seeking clusters, the potential surface of the model studied here is staircase-like, rather than sawtooth-like, with highly collective motions required for passage from one minimum to the next. The surface has several deep basins whose minima correspond to very similar structures, but which are separated by high energy barriers.
Superactivation of an immune response triggered by oligomerized T cell epitopes
Authors: Rötzschke Olaf , Falk Kirsten , Strominger Jack L.
Published: July 2002

The peptides bound to class II major histocompatibility complex (MHC) molecules extend out both ends of the peptide binding groove. This structural feature provided the opportunity to design multivalent polypeptide chains that cross-link class II MHC molecules through multiple, repetitive MHC binding sites. By using recombinant techniques, polypeptide oligomers were constructed that consist of up to 32 copies of an HLA-DR1-restricted T cell epitope. The epitope HA306–318, derived from influenza virus hemagglutinin, was connected by 12- to 36-aa long spacer sequences. These oligomers were found to cross-link soluble HLA-DR1 molecules efficiently and, upon binding to the MHC molecules of a monocyte line, to trigger signal transduction indicated by the enhanced expression of some cell surface molecules. A particularly strong effect was evident in the T cell response. A hemagglutinin-specific T cell clone recognized these antigens at concentrations up to three to four orders of magnitude lower than that of the peptide or the hemagglutinin protein. Both signal transduction in the monocyte and the proliferative response of the T cell were affected greatly by the length of the oligomer (i.e., the number of repetitive units) and the distance of the epitopes within the oligomer (spacing). Thus, the formation of defined clusters of T cell receptor/MHC/peptide antigen complexes appears to be crucial for triggering the immune response and can be used to enhance the antigenicity of a peptide antigen by oligomerizing the epitope.
Ethylene can stimulate
Arabidopsis
hypocotyl elongation in the light
Authors: Smalle Jan , Haegman Mira , Kurepa Jasmina , Van Montagu Marc , Straeten Dominique Van Der
Published: July 2002

Ethylene inhibits hypocotyl elongation in etiolated
Arabidopsis
seedlings. However, when
Arabidopsis
was grown in the light in the presence of ethylene or its precursor 1-aminocyclopropane-1-carboxylic acid (ACC), a marked induction of hypocotyl elongation occurred. This resulted from an increase in cell expansion rather than cell division. The effects of ethylene and ACC were antagonized by the ethylene action inhibitor Ag
+
. The elongation response was absent or weakened in a set of ethylene-insensitive mutants (
etr1-3
,
ein2-1
,
ein3-1
,
ein4
,
ain1-10
,
ein7
). With the exception of
ein4
, the degree of inhibition of hypocotyl elongation was correlated with the strength of the ethylene-insensitive phenotype based on the triple response assay. In addition, the constitutive ethylene response mutant
ctr1-1
, grown in the light, had a longer hypocotyl than the wild type. Exogenous auxin also induced hypocotyl elongation in light-grown
Arabidopsis
. Again, the response was abolished by treatment with Ag
+
, suggesting that ethylene might be a mediator. The results showed that, depending on light conditions, ethylene can induce opposite effects on cell expansion in
Arabidopsis
hypocotyls.
Variable expression of myoglobin among the hemoglobinless Antarctic icefishes
Authors: Sidell Bruce D. , Vayda Michael E. , Small Deena J. , Moylan Thomas J. , Londraville Richard L. , Yuan Meng-Lan , Rodnick Kenneth J. , Eppley Zoe A. , Costello Lori
Published: July 2002

The important intracellular oxygen-binding protein, myoglobin (Mb), is thought to be absent from oxidative muscle tissues of the family of hemoglobinless Antarctic icefishes,
Channichthyidae
. Within this family of fishes, which is endemic to the Southern Ocean surrounding Antarctica, there exist 15 known species and 11 genera. To date, we have examined eight species of icefish (representing seven genera) using immunoblot analyses. Results indicate that Mb is present in heart ventricles from five of these species of icefish. Mb is absent from heart auricle and oxidative skeletal muscle of all species. We have identified a 0.9-kb mRNA in Mb-expressing species that hybridizes with a Mb cDNA probe from the closely related red-blooded Antarctic nototheniid fish,
Notothenia coriiceps
. In confirmation that the 0.9-kb mRNA encodes Mb, we report the full-length Mb cDNA sequence of the ocellated icefish,
Chionodraco rastrospinosus
. Of the eight icefish species examined, three lack Mb polypeptide in heart ventricle, although one of these expresses the Mb mRNA. All species of icefish retain the Mb gene in their genomic DNA. Based on phylogeny of the icefishes, loss of Mb expression has occurred independently at least three times and by at least two distinct molecular mechanisms during speciation of the family.
MurineNkg2dandCd94are clustered within the natural killer complex and are expressed independently in natural killer cells
Authors: Ho Emily L. , Heusel Jonathan W. , Brown Michael G. , Matsumoto Keiko , Scalzo Anthony A. , Yokoyama Wayne M.
Published: July 2002

Natural killer (NK) cells express C-type lectin-like receptors, encoded in the NK gene complex, that interact with major histocompatibility complex class I and either inhibit or activate functional activity. Human NK cells express heterodimers consisting of CD94 and NKG2 family molecules, whereas murine NK cells express homodimers belonging to the Ly-49 family. The corresponding orthologues for other species, however, have not been described. In this report, we used probes derived from the expressed sequence tag database to clone C57BL/6-derived cDNAs homologous to human NKG2-D and CD94. Among normal tissues, murine NKG2-D and CD94 transcripts are highly expressed only in activated NK cells, including both Ly-49A+and Ly-49A−subpopulations. Additionally, mNKG2-D is expressed in murine NK cell clones KY-1 and KY-2, whereas mCD94 expression is observed only in KY-1 cells but not KY-2. Last, we have finely mapped the physical location of theCd94(centromeric) andNkg2d(telomeric) genes betweenCd69and theLy49cluster in the NK complex. Thus, these data indicate the expanding complexity of the NK complex and the corresponding repertoire of C-type lectin-like receptors on murine NK cells.
The crucial role of polymorphonuclear leukocytes in resistance toSalmonella dublininfections in genetically susceptible and resistant mice
Authors: Vassiloyanakopoulos Antonis P. , Okamoto Sharon , Fierer Joshua
Published: July 2002

Macrophages are considered to be the mediators of resistance to extra-intestinalSalmonellainfections. Nevertheless, the initial cellular response toSalmonellainfections consists primarily of polymorphonuclear leukocytes (PMN). To determine whether PMN serve an important function for the infected host, we made mice neutropenic with the rat mAb to RB6–8C5 and infected them i.v. with ≈103Salmonella dublinor an isogenic derivative that lacks the virulence plasmid (LD842). We infected BALB/c mice, which have a point mutation in the macrophage-expressed geneNramp1that makes them susceptible toSalmonella, and BALB/c.D2 congenic mice, which have the wild-typeNramp1gene that makes them resistant toSalmonella. Both mouse strains were resistant to LD842, and neutropenia made only the BALB/c strain susceptible to this infection. Neutropenic congenic mice, however, were susceptible only to wild-typeS. dublin(plasmid+). These results show a complex interplay between plasmid-virulence genes inSalmonella,host macrophages, and PMN. Mice with normal macrophages need PMN to defend against nontyphoidSalmonellathat carry a virulence plasmid but not againstSalmonellawithout virulence plasmids. Mice with a mutantNramp1gene need PMN to defend against allSalmonella, even those that lack virulence plasmids. These results, plus the evidence that PMN killSalmonellaefficientlyin vitro, suggest thatSalmonellahave adapted to grow inside macrophages where they are relatively sheltered from PMN. The adaptations that allowSalmonellato survive in macrophages do not protect them from PMN.
Mammalian glycophosphatidylinositol anchor transfer to proteins and posttransfer deacylation
Authors: Chen Rui , Walter Elizabeth I. , Parker Gregory , Lapurga John P. , Millan Jose L. , Ikehara Yukio , Udenfriend Sidney , Medof M. Edward
Published: July 2002

The glycophosphatidylinositol (GPI) anchors of proteins expressed on human erythrocytes and nucleated cells differ with respect to acylation of an inositol hydroxyl group, a structural feature that modulates their cleavability by PI-specific phospholipase C (PI-PLC). To determine how this GPI anchor modification is regulated, the precursor and protein-associated GPIs in two K562 cell transfectants (ATCC and .48) exhibiting alternatively PI-PLC-sensitive and resistant surface proteins were analyzed and the temporal relationship between GPI protein transfer and acquisition of PI-PLC sensitivity was determined. Nondenaturing PAGE analyses demonstrated that, whereas in .48 transfectants the GPI anchors in decay accelerating factor (DAF) and placental alkaline phosphatase (PLAP) were >95% acylated, in ATCC transfectants, they were 60 and 33% unsubstituted, respectively. In contrast, TLC analyses revealed that putative GPI donors in the two lines were identical and were ≥95% acylated. Studies ofde novoDAF biosynthesis in HeLa cells bearing proteins with >90% unacylated anchors showed that within 5 min at 37°C (or at 18°C, which does not permit endoplasmic reticilum exit), >50% of the anchor in nascent 44-kDa proDAF protein exhibited PI-PLC sensitivity.In vitroanalyses of the microsomal processing of miniPLAP, a truncated PLAP reporter protein, demonstrated that the anchor donor initially transferred to prominiPLAP was acylated and then progressively was deacylated. These findings indicate that (i) the anchor moiety that initially transfers to nascent proteins is acylated, (ii) inositol acylation in mature surface proteins is regulated via posttransfer deacylation, which in general is cell-specific but also can be protein-dependent, and (iii) deacylation occurs in the endoplasmic reticulum immediately after GPI transfer.
Mutation frequency declines during spermatogenesis in young mice but increases in old mice
Authors: Walter Christi A. , Intano Gabriel W. , McCarrey John R. , McMahan C. Alex , Walter Ronald B.
Published: July 2002

Five percent of live-born human offspring will have a genetic disorder. Of these, 20% are because of germ-line
de novo
mutations. Several genetic diseases, such as neurofibromatosis and Duchenne muscular dystrophy, are associated with a high percentage of
de novo
germ-line mutations. Until recently, a direct analysis of spontaneous mutation frequencies in mammalian germ cells has been prevented by technical limitations. We have measured spontaneous mutation frequencies in a
lacI
transgene by using enriched populations of specific spermatogenic cell types. Similar to previously published results, we observed a lower mutation frequency for seminiferous tubule cell preparations, which contain all stages of spermatogenesis, relative to somatic tissues. We made the unexpected observation of a decline in mutation frequency during spermatogenesis, such that the mutation frequencies of type B spermatogonia and all subsequent stages of spermatogenesis are lower than the frequency for primitive type A spermatogonia. In addition, spermatogenic cells from old mice have significantly increased mutation frequencies compared with spermatogenic cells from young or middle-aged mice. Finally, the mutation frequency was observed to increase during spermiogenesis in postreplicative cell types when spermatogenic cells were obtained from old mice.
Identification of the lactococcal exonuclease/recombinase and its modulation by the putative Chi sequence
Authors: Karoui Meriem El , Ehrlich Dusko , Gruss Alexandra
Published: July 2002

Studies of RecBCD–Chi interactions in
Escherichia coli
have served as a model to understand recombination events in bacteria. However, the existence of similar interactions has not been demonstrated in bacteria unrelated to
E. coli
. We developed an
in vivo
model to examine components of dsDNA break repair in various microorganisms. Here, we identify the major exonuclease in
Lactococcus lactis
, a Gram-positive organism evolutionarily distant from
E. coli
, and provide evidence for exonuclease–Chi interactions. Insertional mutants of
L. lactis
, screened as exonuclease-deficient, affected a single locus and resulted in UV sensitivity and recombination deficiency. The cloned lactococcal genes (called
rexAB
) restored UV resistance, recombination proficiency, and the capacity to degrade linear DNA, to an
E. coli recBCD
mutant. In this context, DNA degradation is specifically blocked by the putative lactococcal Chi site (5′-GCGCGTG-3′), but not by the
E. coli
Chi (5′-GCTGGTGG-3′) site. RexAB-mediated recombination was shown to be stimulated ≈27-fold by lactococcal Chi. Our results reveal that RexAB fulfills the biological roles of RecBCD and indicate that its activity is modulated by a short DNA sequence. We speculate that exonuclease/recombinase enzymes whose activities are modulated by short DNA sequences are widespread among bacteria.
A cytochrome P450 terpenoid hydroxylase linked to the suppression of insect juvenile hormone synthesis
Authors: Sutherland T. D. , Unnithan G. C. , Andersen J. F. , Evans P. H. , Murataliev M. B. , Szabo L. Z. , Mash E. A. , Bowers W. S. , Feyereisen R.
Published: July 2002

A cDNA encoding a cytochrome P450 enzyme was isolated from a cDNA library of the corpora allata (CA) from reproductively active
Diploptera punctata
cockroaches. This P450 from the endocrine glands that produce the insect juvenile hormone (JH) is most closely related to P450 proteins of family 4 and was named CYP4C7. The
CYP4C7
gene is expressed selectively in the CA; its message could not be detected in the fat body, corpora cardiaca, or brain, but trace levels of expression were found in the midgut and caeca. The levels of CYP4C7 mRNA in the CA, measured by ribonuclease protection assays, were linked to the activity cycle of the glands. In adult females,
CYP4C7
expression increased immediately after the peak of JH synthesis, reaching a maximum on day 7, just before oviposition. mRNA levels then declined after oviposition and during pregnancy. The CYP4C7 protein was produced in
Escherichia coli
as a C-terminal His-tagged recombinant protein. In a reconstituted system with insect NADPH cytochrome P450 reductase, cytochrome
b
5
, and NADPH, the purified CYP4C7 metabolized (2
E
,6
E
)-farnesol to a more polar product that was identified by GC-MS and by NMR as (10
E
)-12-hydroxyfarnesol. CYP4C7 converted JH III to 12-
trans
-hydroxy JH III and metabolized other JH-like sesquiterpenoids as well. This ω-hydroxylation of sesquiterpenoids appears to be a metabolic pathway in the corpora allata that may play a role in the suppression of JH biosynthesis at the end of the gonotrophic cycle.
Assembly of cyclin D-dependent kinase and titration of p27
Kip1
regulated by mitogen-activated protein kinase kinase (MEK1)
Authors: Cheng Mangeng , Sexl Veronika , Sherr Charles J. , Roussel Martine F.
Published: July 2002

A constitutively active form of mitogen-activated protein kinase kinase (MEK1) was synthesized under control of a zinc-inducible promoter in NIH 3T3 fibroblasts. Zinc treatment of serum-starved cells activated extracellular signal-regulated protein kinases (ERKs) and induced expression of cyclin D1. Newly synthesized cyclin D1 assembled with cyclin-dependent kinase-4 (CDK4) to form holoenzyme complexes that phosphorylated the retinoblastoma protein inefficiently. Activation of the MEK1/ERK pathway neither triggered degradation of the CDK inhibitor kinase inhibitory protein-1 (p27
Kip1
) nor led to activation of cyclin E- and A-dependent CDK2, and such cells did not enter the DNA synthetic (S) phase of the cell division cycle. In contrast, zinc induction of active MEK1 in cells also engineered to ectopically overexpress cyclin D1 and CDK4 subunits generated levels of cyclin D-dependent retinoblastoma protein kinase activity approximating those achieved in cells stimulated by serum. In this setting, p27
Kip1
was mobilized into complexes containing cyclin D1; cyclin E- and A-dependent CDK2 complexes were activated; and serum-starved cells entered S phase. Thus, although the activity of p27
Kip1
normally is canceled through a serum-dependent degradative process, overexpressed cyclin D1-CDK complexes sequestered p27
Kip1
and reduced the effective inhibitory threshold through a stoichiometric mechanism. A fraction of these cells completed S phase and divided, but they were unable to continuously proliferate, indicating that other serum-responsive factors ultimately became rate limiting for cell cycle progression. Therefore, the MEK/ERK pathway not only acts transcriptionally to induce the cyclin D1 gene but functions posttranslationally to regulate cyclin D1 assembly with CDK4 and to thereby help cancel p27
Kip1
-mediated inhibition.
Plasmodium gallinaceum
preferentially invades vesicular ATPase-expressing cells in
Aedes aegypti
midgut
Authors: Shahabuddin Mohammed , Pimenta Paulo F. P.
Published: July 2002

Penetration of the mosquito midgut epithelium is obligatory for the further development of
Plasmodium
parasites. Therefore, blocking the parasite from invading the midgut wall disrupts the transmission of malaria. Despite such a pivotal role in malaria transmission, the cellular and molecular interactions that occur during the invasion are not understood. Here, we demonstrate that the ookinetes of
Plasmodium gallinaceum
, which is related closely to the human malaria parasite
Plasmodium falciparum
, selectively invade a cell type in the
Aedes aegypti
midgut. These cells, unlike the majority of the cells in the midgut, do not stain with a basophilic dye (toluidine blue) and are less osmiophilic. In addition, they contain minimal endoplasmic reticulum, lack secretory granules, and have few microvilli. Instead, these cells are highly vacuolated and express large amounts of vesicular ATPase. The enzyme is associated with the apical plasma membrane, cytoplasmic vesicles, and tubular extensions of the basal membrane of the invaded cells. The high cost of insecticide use in endemic areas and the emergence of drug resistant malaria parasites call for alternative approaches such as modifying the mosquito to block the transmission of malaria. One of the targets for such modification is the parasite receptor on midgut cells. A step toward the identification of this receptor is the realization that malaria parasites invade a special cell type in the mosquito midgut.
Subsurface tumor progression investigated by noninvasive optical second harmonic tomography
Authors: Guo Yici , Savage Howard E. , Liu Feng , Schantz Stimson P. , Ho P. P. , Alfano R. R.
Published: July 2002

Nonlinear optical imaging with femtosecond (10
−15
-second) laser technology was used to evaluate the subsurface tumor progression in control, dysplasia, and cancerous 7,12-dimethylbenz[
a
]anthracene-treated hamster cheek pouch mucosa tissues. Two-dimensional images of hamster cheek pouch mucosa tissues were obtained by scanning the second harmonic signal at various sagittal and axial positions. The spatial mapping of the second harmonic signals showed depth differentiation between normal, dysplasia, and a more advanced cancerous state. This nonlinear optical method offers a noninvasive
in situ
imaging tool to the medical community.
Peroxynitrite reaction products of 3′,5′-di
-O-
acetyl-8-oxo-7,8-dihydro-2′-deoxyguanosine
Authors: Niles Jacquin C. , Burney Samar , Singh Sukhjeet P. , Wishnok John S. , Tannenbaum Steven R.
Published: July 2002

Of the DNA bases, peroxynitrite (ONOO
−
) is most reactive toward 2′-deoxyguanosine (dGuo), but even more reactive with 8-oxo-7,8-dihydro-2′-deoxyguanosine (8-oxodGuo), requiring a 1,000-fold excess of dGuo to provide 50% protection against the reaction with 8-oxodGuo. Therefore, it seems reasonable that 8-oxodGuo is a potentially important target in DNA and that the structures of the reaction products with ONOO
−
should be characterized. Using 3′,5′-di
-O-
Ac-8-oxodGuo as a model compound, the reaction products with ONOO
−
have been isolated and identified under simulated physiological reaction conditions (phosphate/bicarbonate buffer at pH 7.2). The major reaction product, II, is unstable and undergoes base-mediated hydrolysis to 2,5-diaminoimidazol-4-one, IIa, and 3-(3,5-di
-O-
Ac-2-deoxy-β-
d
-
erythro
-pentofuranosyl)-5-iminoimidazolidine-2,4-dione, IIb. The latter compound further hydrolyzes to 3-(3,5-di
-O-
Ac-2-deoxy-β-
d
-
erythro
-pentofuranosyl)oxaluric acid, IIc. Other products include 3-(3,5-di
-O-
Ac-2-deoxy-β-
d
-
erythro
-pentofuranosyl)-2,4,6-trioxo-[1,3,5]triazinane-1-carboxamidine, I, which further hydrolyzes to 1-(3,5-di
-O-
Ac-2-deoxy-β-
d
-
erythro
-pentofuranosyl)cyanuric acid, Ia. 1-(3,5-di
-O-
Ac-2-deoxy-β-
d
-
erythro
-pentofuranosyl)parabanic acid, III, is a minor product that also may contribute to formation of IIc. The major products formed in these reactions are biologically uncharacterized but are similar to modified DNA bases that have been shown to be both premutagenic and blocks to DNA polymerization.
Long-term expression of protein kinase C in adult mouse hearts improves postischemic recovery
Authors: Tian Rong , Miao Wenfeng , Spindler Matthias , Javadpour Maryam M. , McKinney Ronald , Bowman Joel C. , Buttrick Peter M. , Ingwall Joanne S.
Published: July 2002

Activation of protein kinase C (PKC) protects the heart from ischemic injury; however, its mechanism of action is unknown, in part because no model for chronic activation of PKC has been available. To test whether chronic, mild elevation of PKC activity in adult mouse hearts results in myocardial protection during ischemia or reperfusion, hearts isolated from transgenic mice expressing a low level of activated PKCβ throughout adulthood (β-Tx) were compared with control hearts before ischemia, during 12 or 28 min of no-flow ischemia, and during reperfusion. Left-ventricular-developed pressure in isolated isovolumic hearts, normalized to heart weight, was similar in the two groups at baseline. However, recovery of contractile function was markedly improved in β-Tx hearts after either 12 (97 ± 3% vs. 69 ± 4%) or 28 min of ischemia (76 ± 8% vs. 48 ± 3%). Chelerythrine, a PKC inhibitor, abolished the difference between the two groups, indicating that the beneficial effect was PKC-mediated.
31
P NMR spectroscopy was used to test whether modification of intracellular pH and/or preservation of high-energy phosphate levels during ischemia contributed to the cardioprotection in β-Tx hearts. No difference in intracellular pH or high-energy phosphate levels was found between the β-Tx and control hearts at baseline or during ischemia. Thus, long-term modest increase in PKC activity in adult mouse hearts did not alter baseline function but did lead to improved postischemic recovery. Furthermore, our results suggest that mechanisms other than reduced acidification and preservation of high-energy phosphate levels during ischemia contribute to the improved recovery.
Critical role of conserved proline residues in the transmembrane segment 4 voltage sensor function and in the gating of L-type calcium channels
Authors: Yamaguchi Hiroshi , Muth James N. , Varadi Maria , Schwartz Arnold , Varadi Gyula
Published: July 2002

The fourth transmembrane segment (S4) has been shown to function as
a voltage sensor in voltage-gated channels. On membrane depolarization,
a stretch of S4 moves outward and initiates a number of conformational
changes that ultimately lead to channel opening. Conserved proline
residues are in the middle of the S4 of motifs I and III in
voltage-dependent Ca
2+
channels. Because proline often
introduces a “kink” into a helical structure of proteins, these
residues might have an intrinsic function in the voltage sensor. Here,
we report that the removal of S4 prolines results in a dramatic
shortening of channel open time whereas the introduction of extra
prolines to the corresponding positions in motif IIS4 and IVS4
lengthens channel open time. The number of S4s with a proline residue
showed a clear positive correlation with the mean open time of the
channel. The mean open time was >11-fold longer for a channel
mutagenized to have prolines in all four S4s compared with a channel
that had no prolines in the S4 region. Additionally, prolines in the
S4s slowed activation kinetics and shifted the voltage dependence of
activation and inactivation in a hyperpolarized direction. Our results
strongly suggest that proline residues in the S4s are critical for
stabilizing the open state of the channel. Moreover, it is suggested
that motif IS4 and IIIS4 contribute to the channel opening more
efficiently than motif IIS4 and IVS4.
A wound- and systemin-inducible polygalacturonase in tomato leaves
Authors: Bergey Daniel R. , Orozco-Cardenas Martha , de Moura Daniel S. , Ryan Clarence A.
Published: July 2002

Oligogalacturonide fragments that activate defensive genes in plant
leaves heretofore have been thought to be generated only by
pathogen-derived pectin-degrading enzymes, because polygalacturonase
(PG) activity has not been reported in leaves. Here, we report that
mRNAs encoding a PG catalytic subunit protein and its regulatory
(β-subunit) protein are expressed in tomato leaves in response to
wounding, systemin, and oligosaccharide elicitors. Synthesis of the two
subunits in response to wounding is systemic and is accompanied by an
increase in PG activity in extracts from both wounded and unwounded
leaves. The finding that PG subunit mRNAs and PG enzyme activity are
induced by wounding indicates that herbivore attacks can produce
endogenous oligogalacturonide elicitors that may be
involved in the local and systemic activation of defense responses
against both herbivores and pathogens.
Polarity of recombination in transformation of
Streptococcus pneumoniae
Authors: Pasta Franck , Sicard Michel A.
Published: July 2002

In transformation of
Streptococcus pneumoniae
DNA enters the cell as single-strand fragments and integrates into the chromosome by homologous recombination. Deletions and insertions of a few hundred base pairs frequently stop the recombination process of a donor strand. In this work we took advantage of such interruptions of recombination to compare the transformation efficiencies of the segments 5′- and 3′-ward from a deletion. The deletion was created in the center of a fragment of the
ami
locus, and sites around the deletion were labeled by a frameshift generating a restriction site. Heteroduplexes were constructed containing two restriction sites on one strand and two different ones on the complementary strand.
ami
+
bacteria were transformed with such heteroduplexes.
ami
−
transformants were isolated and individually underwent amplification of the transformed
ami
region. We have obtained two kinds of amplification products: short when the deletion was integrated, long when recombination stops at the deletion. Each long fragment was tested by the four restriction enzymes to detect which strand and which side of the deletion had recombined. We found that 80% of the cuts were located 5′ to the deletion, showing that,
in vivo
, the 5′ side is strongly favored by recombination. Further results suggest that exchanges occurring from 5′ to 3′ relative to the donor strand are more efficient than in the opposite direction, thus accounting for the 5′ preference.
Targeted disruption of an erythrocyte binding antigen in
Plasmodium falciparum
is associated with a switch toward a sialic acid-independent pathway of invasion
Authors: Reed Michael B. , Caruana Sonia R. , Batchelor Adrian H. , Thompson Jennifer K. , Crabb Brendan S. , Cowman Alan F.
Published: July 2002

Erythrocyte invasion by
Plasmodium
requires molecules present both on the merozoite surface and within the specialized organelles of the apical complex. The
Plasmodium
erythrocyte binding protein family includes the
Plasmodium falciparum
sialic acid-binding protein, EBA-175 (erythrocyte binding antigen-175), which binds sialic acid present on glycophorin A of human erythrocytes. We address the role of the conserved 3′-cysteine rich region, the transmembrane, and cytoplasmic domains through targeted gene disruption. Truncation of EBA-175 had no measurable effect on either the level of EBA-175 protein expression or its subcellular localization. Similarly, there appears to be no impairment in the ability of soluble EBA-175 to be released into the culture supernatant after schizont rupture. Additionally, the 3′-cys rich region, transmembrane, and cytoplasmic domains of EBA-175 are apparently non-essential for merozoite invasion. In contrast, erythrocyte invasion via the EBA-175/glycophorin A route appears to have been disrupted to such a degree that the mutant lines have undergone a stable switch in invasion phenotype. As such, EBA-175 appears to have been functionally inactivated within the truncation mutants. The sialic acid-independent invasion pathway within the mutant parasites accounts for approximately 85% of invasion into normal erythrocytes. These data demonstrate the ability of
P. falciparum
to utilize alternate pathways for invasion of red blood cells, a property that most likely provides a substantial survival advantage in terms of overcoming host receptor heterogeneity and/or immune pressure.
Phosphatase activity of histidine kinase EnvZ without kinase catalytic domain
Authors: Zhu Yan , Qin Ling , Yoshida Takeshi , Inouye Masayori
Published: July 2002

Most histidine kinases are bifunctional enzymes having both kinase and phosphatase activities. The cytoplasmic kinase domain of EnvZ, a transmembrane histidine kinase functioning as an osmosensor in
Escherichia coli
, consists of two distinct functional subdomains: domain A [EnvZc(223–289)] and domain B [EnvZc(290–450)]. NMR studies demonstrated that domain A consists of a four-helix bundle serving as a dimerization and phosphotransfer domain, and domain B functions as the ATP-binding and catalytic domain. Here we demonstrate that domain A by itself has the phosphatase activity both
in vitro
and
in vivo
. This phosphatase activity is Mg
2+
dependent but is not activated by ADP, ATP, or adenosine 5′-[β,γ-imido]triphosphate (AMPPNP), each of which may serve as a cofactor for the EnvZ phosphatase activity. Domain B showed a small but distinct effect on the domain A phosphatase activity only in the presence of ADP or AMPPNP. However, when domain B was covalently linked to domain A, dramatic cofactor-dependent enhancement of the phosphatase activity was observed. Extending domain A for another 75 residues at the C terminus or 44 residues at the N terminus did not enhance its phosphatase activity. Substitution mutations at His-243, the autophosphorylation site, demonstrate that the His residue plays an essential role in the phosphatase activity. The so-called X-region mutant L288P that is known to specifically abolish the phosphatase activity in EnvZ had no effect on the domain A phosphatase function. We propose that the EnvZ phosphatase activity is regulated by relative positioning of domains A and B, which is controlled by external signals. We also propose that the His-243 residue participates in both kinase and phosphatase reactions.
Prevention of passively transferred experimental autoimmune myasthenia gravis by a phage library-derived cyclic peptide
Authors: Venkatesh Natarajan , Im Sin-Heyog , Balass Moshe , Fuchs Sara , Katchalski-Katzir Ephraim
Published: July 2002

Many pathogenic antibodies in myasthenia gravis (MG) and its animal model, experimental autoimmune MG (EAMG), are directed against the main immunogenic region (MIR) of the acetylcholine receptor (AcChoR). These antibodies are highly conformation dependent; hence, linear peptides derived from native receptor sequences are poor candidates for their immunoneutralization. We employed a phage-epitope library to identify peptide-mimotopes capable of preventing the pathogenicity of the anti-MIR mAb 198. We identified a 15-mer peptide (PMTLPENYFSERPYH) that binds specifically to mAb 198 and inhibits its binding to AcChoR. A 10-fold increase in the affinity of this peptide was achieved by incorporating flanking amino acid residues from the coat protein as present in the original phage library. This extended peptide (AEPMTLPENYFSERPYHPPPP) was constrained by the addition of cysteine residues on both ends of the peptide, thus generating a cyclic peptide that inhibited the binding of mAb 198 to AcChoR with a potency that is three orders of magnitude higher when compared with the parent library peptide. This cyclic peptide inhibited thein vitrobinding of mAb 198 to AcChoR and prevented the antigenic modulation of AcChoR caused by mAb 198 in human muscle cell cultures. The cyclic peptide also reacted with several other anti-MIR mAbs and the sera of EAMG rats. In addition, this peptide blocked the ability of mAb 198 to passively transfer EAMG in rats. Further derivatization of the cyclic peptide may aid in the design of suitable synthetic mimotopes for modulation of MG.
Family business in Russia: the path to middle class?
Authors: Barkhatova Nonna , McMylor Peter , Mellor Rosemary
Published: July 2002

The paper seeks to explore via a series of interview‐based case studies aspects of the emergence of an entrepreneurial middle‐class in Russia. The paper notes the origins of those studied in the professional or highly skilled workers in the former Soviet Union. The paper reveals the complexity and fragility of the circumstances of these entrepreneurs and suggests that commentary in both Russia and the West that pins its hopes for social stability on the emergence of a new property owning middle class in Russia are, at best, premature.
Effet d'un scénario d'interaction dans la résolution d'un problème chez des enfants de 5–6 ans
Authors: Demerval René
Published: July 2002

Cette étude a pour objectif de spécifier l'hypothèse selon laquelle les progrès individuels consécutifs à une corèsolution de problème sont liés aux rôles que s'attribuent spontanément les partenaires. Des enfants de 5–6 ans sont répartis en trois groupes expérimentaux. Dans un groupe, dit en interaction socio‐règulée, des dyades sont constituées et chaque partenaire se voit attribuer un rôle ajusté à la résolution de problème. Dans un autre groupe, également constitué de dyades, les sujets sont libres d'organiser leur activité de résolution. Enfin, le dernier groupe est composé de sujets ayant à résoudre seuls le problème. Au cours du traitement expérimental, la résolution de problème est facilitée par la présence d'un outil qui régule l'activité des sujets. Il est supposé que les rôles attribués aux sujets du groupe en interaction socio‐régulée permettent la médiation sémiotique de la régulation et la différenciation des activités de résolution. Les résultats indiquent que les sujets en interaction libre ont les meilleures performances uniquement au cours du traitement expérimental et que les sujets en interaction socio‐régulée ont les meilleures performances uniquement lors du post‐test individuel différé. Les résultats sont discutés en référence aux systèmes de régulation de l'activité dans lesquels sont insérés les sujets et aux mécanismes permettant l'appropriation de cette régulation.
Muslim Identity in the Balkans before the Establishment of Nation States
Authors: Bieber Florian
Published: July 2002

In analyzing national and ethnic identities in the Balkans, one notices a “delay” in the development of the Muslim national identity. The Bosniaks and Albanians, for example, developed a national consciousness in the late nineteenth and early twentieth century. In contrast to the Southeastern European Christians, the Muslim inhabitants followed the official religion of the dominant political class of the Ottoman Empire—Islam—a faith that (theoretically, at least) privileged religious belief over ethnicity or nationalism. These two concepts, alien to Ottoman intellectual tradition, became fully understood by the Ottoman elite only in the early twentieth century. Although the Muslims under Ottoman rule often perceived themselves as different from their co-religionist rulers in Istanbul, as shall be demonstrated in this paper, they nevertheless shared the religion of the rulers of the Empire and practised a religion that suppressed the development of national identity far more explicitly than did Christianity. Thus, it was the decline of the Ottoman Empire in the nineteenth century, and the consequent recognition that this state was ceasing to protect the interests and identity of the Muslim population in Southeastern Europe, which led to the development of ethnic and national identity among the Muslims.
Women in Television in the Multi-Channel Age
Authors: Thynne Lizzie
Published: July 2002

This article explores the impact of structural and technological change on women's employment in the UK television industry. It looks at the challenges faced by women in working in what has become since the mid-1980s a largely freelance industry where short-term contracts, informal recruitment procedures and long, unpredictable work schedules mean that women find it increasingly difficult to combine a career and family. Through case studies of individual careers, of a women's magazine programme for S4C Digital and a survey of women's credits on a selection of the newer channels (Sky One, UK Living and Channel 5), it argues that technological advances in digital transmission and production will not improve working conditions and opportunities for women's participation in all areas of the industry if they continue to replicate existing practice.
Motherhood in the East–West Encounter: Pandita Ramabai's Negotiation of ‘Daughterhood’ and Motherhood
Authors: Kosambi Meera
Published: July 2002

The female East–West encounter often pivoted upon the motherhood role played by the representatives of the empire. This article aims to explore the complexities of the construction and enactment of this role. The analysis focuses on a cameo of triangular interpersonal relationships formed by Pandita Ramabai, an Indian Brahmin scholar who converted to Christianity in 1883 during her stay in England for higher studies, her little daughter Manorama who was baptized at the same time and Ramabai's spiritual mother, the Anglican Sister Geraldine who was deeply and possessively attached to Manorama. After situating motherhood in its international discursive context, the article examines the two tension-filled sets of motherhood and daughterhood inherent in this triad, with the help of Ramabai's published letters and correspondence which were compiled and edited by Geraldine (who made Ramabai's maternal inadequacies her dominant subtext) and of Manorama's unpublished letters to Geraldine, her ‘grandmother’. The article argues that a British missionary nun's successful exercise of the motherhood role which she spontaneously assumed towards an Indian convert was contingent upon the convert's adherence to the racially and culturally inferior stereotype and unquestioning submission to the new faith as well as to colonial authority. Such conformity and acceptance alone allowed deep ‘maternal’ bonding (overlooking racial differences) which was too fragile to withstand any contestation or exercise of agency by the convert. The overarching patriarchal ethos of the Church, internalized by the missionary nun, was also a significant determinant of her treatment of the women converts in various ways.
Freelancers, Temporary Wives, and Beach-Boys: Researching Sex Work in the Caribbean
Authors: Kempadoo Kamala
Published: July 2002

This article presents insights from a research project on sex work that took place in the Caribbean region during 1997–8. First it briefly summarizes common themes in historical and contemporary studies of sex work in the region, then describes the aims, methodology, and main trends of the project. It pays particular attention to the differences between definitions and experiences of sex work by female and male sex workers and of male and female sex tourists, as well as describing conditions in the Caribbean sex trade. Finally the article identifies some implications of the complexity in the region that were uncovered through the research project for feminist theorizing about sex work.
‘Been There, Seen it, Done it, I've Got the T-shirt’: British Sex Worker's Reflect on Jobs, Hopes, the Future and Retirement
Authors: Rickard Wendy
Published: July 2002

While analysis of what takes people into prostitution has been widely documented, this article explores the way adult ‘30 something’ prostitutes consider their futures and the ideas they have about leaving or staying in prostitution. Drawing on contested notions of prostitution as ‘work’ and the broader context of life-history research with sex workers, it explores the experiences that frame prostitutes’ own narratives about their working lives and futures. An illustrative range of five life-history accounts from British sex workers are analysed as ‘imagined’ curriculum vitae, listing emergent categories of: aliases, education, interests, thoughts on retirement, financial planning, getting older, hopes and ambitions and fantasy futures. These ‘stories’ are analysed looking at ways they inform on-going feminist debates about the realities of (voluntary adult) sex workers’ concerns. They point again to the relevance for sex workers and feminists of understanding sex work as ‘a job’.