bluuebunny/crossref_metadata_2025 huggingface dataset:
Demographic viability of populations of Silene regia in midwestern prairies: relationships with fire management, genetic variation, geographic location, population size and isolation
Authors: Menges Eric S. , Dolan Rebecca W.
Published: May 2003

1  We studied the demographic viability of populations of a long‐lived iteroparous prairie perennial, Silene regia, in relation to management regimes, population sizes, geographical region (Ohio and Indiana vs. Missouri and Arkansas), degree of isolation and amount of genetic variation. Demographic data were collected from 16 populations for up to 7 years.

2  This species has high survivorship, slow growth, frequent flowering and episodic seedling recruitment. Matrix projection methods were used to summarize population performance with and without recruitment. Median finite rates of increase by population varied from 0.57 to 1.82 and from 0.44 to 0.99, respectively.

3  Populations with the highest rates of increase had been burned. Six of eight populations, for which stochastic modelling predicted persistence for 1000 years, included fire in their management. None of the five populations with predicted 100‐year extinction probabilities of 100% was managed for conservation or burned. An intermediate group of three populations with at least 10% probability of extinction between 100 and 1000 years was not managed, but was none the less kept open by mowing and herbicide application.

4  Analysis of composite elasticities showed that growth and fecundity terms were higher for growing (vs. declining) populations and that growth elasticity was higher in burned than unburned populations. Lack of burning shifts the elasticity spectrum from that typical of open habitat herbs (higher growth and fecundity elasticities) to values usually found for closed habitat herbs (higher survival elasticities).

5  In multivariate analyses predicting finite rates of increase (with and without recruitment), fire management and region were the strongest predictors, followed by genetic variation, population size, isolation and interactions of population size and fire, and region and fire. Populations with the highest rates of increase were burned, eastern, more genetically diverse, larger and less isolated. Discrimination of populations with different extinction risks (three classes) was related mainly to fire, genetic variation and region.

6  Most of these conclusions support conservation biology predictions that population viability will be highest in larger, less‐isolated, more genetically diverse populations. However, management and geographic trends have overriding roles affecting demographic viability. Habitat fragmentation and genetic depletion have the potential to threaten residual prairie populations of S. regia, but lack of fire management appears to be the primary short‐term threat.
Interactive effects of elevation and burial with wrack on plant community structure in some Rhode Island salt marshes
Authors: Brewer J. Stephen , Levine Jonathan M. , Bertness Mark D.
Published: May 2003

1  The effects of disturbances and elevation on marsh plant communities were examined using experimental disturbances along an elevation gradient in marshes with different disturbance histories. In addition, differences in species composition among five marshes were determined at elevations at which the greatest concentration of burial by wrack occurred.

2  Experimental wrack burial generally caused significant mortality of the high‐marsh competitive dominants, Juncus gerardi and Spartina patens, and strongly increased the abundance of the fugitive perennial, Distichlis spicata.

3  The effects of experimental wrack burial interacted strongly with abiotic factors associated with elevation to influence the distributions of both competitive dominants and annual fugitive plants.

4  Frequent wrack burial in a marsh appears to lead to a persistent assemblage of plants dominated by competitively subordinate fugitives. This assemblage of fugitives tends to occur at intermediate elevations within the marsh, where wrack gets stranded for long periods of time and where the resistance of Juncus gerardi to wrack burial is lowest.

5  We suggest that wrack‐burial disturbances interact strongly with marsh elevation to influence the zonation of plants in New England salt marshes, and discuss some implications of our results.
Flat colonic adenomas in Malaysia: Fact or fancy?
Authors: RAJENDRA SHANMUGARAJAH , KUTTY KANNAN , KARIM NORAIN
Published: May 2003

Background: Some two‐thirds of colorectal carcinomas arise from adenomatous polyps, and as such, screening by colonoscopy and polyp removal should significantly reduce colorectal cancer. This has not been the case, as evidenced by recent studies, which revealed that endoscopy failed to prevent up to 50% of all subsequent carcinomas. Flat or depressed adenomas, frequently reported from Japan but rarely elsewhere, might explain the ‘missed carcinomas.’ Detection of flat adenomas has not been previously reported from Malaysia.

Methods: In the present prospective study, 426 consecutive patients underwent colonoscopic examination between March 1997 and January 2000, for a variety of bowel symptoms. The examinations were performed by an experienced endoscopist using a standard colonoscope and methylene blue dye spraying technique. Macroscopically, flat adenomas were defined using the criteria proposed by Sawada.

Results: Twenty‐nine adenomas were identified in 12 patients, of which 15 were polypoid and 14 were flat, with no depressed lesions. Eight polypoidal lesions and all the flat adenomas contained mild or moderate areas of epithelial dysplasia. Seven severely dysplastic polyps were identified. One Duke's A polypoidal cancer and two advanced carcinomas were also found. All the severely dysplastic lesions and Duke's A carcinomas were found in polyps greater than 10 mm in mean size. The flat adenomas were all less than 5 mm in size.

Conclusions: A significant proportion of colonic adenomas in Malaysian patients appear as small flat lesions, which could easily be missed during endoscopy. Increased recognition and treatment of flat adenomas among colonoscopists is warranted.
Intrathoracic gastric volvulus mimicking pyloric stenosis
Authors: Munoz JJ , Mansul AJ , Malpas TJ , Steinbrecher HA
Published: May 2003

Abstract:  A 5‐week‐old‐infant presented to hospital following the acute onset of non‐bilious vomiting with clinical and acid−base features suggestive of pyloric stenosis. A chest radiograph obtained because of intercurrent infection unexpectedly revealed a left‐sided congenital diaphragmatic hernia. A barium meal demonstrated the presence of an intrathoracic gastric volvulus, requiring urgent surgical management. We discuss the presentation and management of this rare surgical cause of non‐bilious vomiting in infancy.
Epidemiology of childhood nocturnal enuresis in Malaysia
Authors: Kanaheswari Y
Published: May 2003

Objectives:  To estimate the prevalence of nocturnal enuresis in primary school children in Malaysia and to determine the factors associated with primary nocturnal enuresis.

Methods:  This was a cross‐sectional survey. A total of 3371 self‐administered questionnaires were distributed to parents of children aged 7, 9 and 12 years attending four primary schools in the city. The ICD‐10 definition of enuresis was used.

Results:  From an overall response rate of 73.8%, nocturnal enuresis was reported in 200 children (8%), primary nocturnal enuresis in 156 children (6.2%) and secondary nocturnal enuresis in 44 children (1.8%). Fifty‐three percent of those with primary enuresis had a positive family history, and 54% had two or more wet nights per week. Eighty‐seven percent had not sought any form of treatment despite 74% admitting to being embarrassed. Using logistic regression analysis, only three factors were significant predictors of primary nocturnal enuresis. These were: (i) younger age (P < 0.001); (ii) male sex (P < 0.033); and (iii) Indian ethnic group (P < 0.044) compared to Chinese.

Conclusion:  The prevalence of nocturnal enuresis in urban‐dwelling Malaysian children is similar to that reported from Korea and Taiwan but appears to be lower than that reported from developed countries. Predictive factors associated with primary nocturnal enuresis included lower age group, male sex and Indian ethnicity.
Acute administration of conjugated equine oestrogen does not improve exercise‐induced myocardial ischaemia in men with coronary artery disease
Authors: Davis S. R. , Bradbury J. , Bell R. , Johns J. A.
Published: May 2003

Background:  The parenteral administration of oestradiol acutely protects against exercise‐induced myocardial ischaemia in women, but whether this effect is sex ­specific is not known.

Aims:  The effects of acutely administered conjugated equine oestrogen on exercise‐induced myocardial ischaemia in men with established coronary heart disease were investigated in a randomized, placebo‐­controlled, double‐blind cross‐over trial.

Methods:  Twenty men, aged 62 ± 11.6 years, with reproducible exercise‐induced myocardial ischaemia were treated with either intravenous conjugated equine oestrogen (25 mg) or saline prior to undergoing an exercise stress test. Primary end‐points were total exercise time and time to 1 mm ST‐segment depression.

Results:  All participants completed the protocol. Total exercise time exceeded the baseline value in 17 of the 20 men following saline, and in 17 of the 20 men following oestrogen pretreatment. Time to 1 mm ST‐segment depression exceeded the baseline value in 14 of the 19 men following saline, and following oestrogen administration, exceeded baseline in 13 of the 19 men. There was no significant difference between the two treatments in either time to 1 mm ST‐segment depression or total exercise time. A period effect was apparent for total exercise time (P = 0.05) but not for time to ST‐segment depression.

Conclusion:  Acute parenteral oestrogen therapy did not increase total exercise time or time to the onset of electrocardiographic changes of ischaemia in men with chronic stable coronary artery disease. These findings contrast the favourable effects of oestrogen in women in comparable studies and indicate a sex specificity for the acute cardiovascular effects of oestrogen. (Intern Med J 2003; 33: 221−224)
Chronic renal insufficiency and renoprotective strategies
Authors: Wyburn K. R. , Horvath J. S.
Published: May 2003

The increasing incidence in the number of patients with end‐stage renal disease is a major public health and economic concern. There is growing awareness that early detection and intervention can have a significant impact on delaying the progression of chronic renal insufficiency and the associated comorbidities. By implementing renoprotective measures early, even modest improvements can equate to significant benefits in the long term, hence the importance of identifying at‐risk patients and early referrals to specialist multidisciplinary teams. In this review, some of the evidence‐based renoprotective measures available are examined. (Intern Med J 2003; 33: 237−241)
Bacterial community structure and function in a metal‐working fluid
Authors: Van Der Gast Christopher J. , Whiteley Andrew S. , Lilley Andrew K. , Knowles Christopher J. , Thompson Ian P.
Published: May 2003

The diversity of bacterial populations colonizing spatially and temporally separated samples of the same metal‐working fluid (MWF) formulation was investigated. Analyses were performed with a view to improve strategies for bioaugmentation of waste MWF in bioreactor systems and prevention of in‐use MWF biodeterioration in engineering workshops. Significantly, complementary phenotypic, genotypic and in situ methods revealed that the bacterial communities in operationally exhausted MWFs had low diversity and were similar in species composition from different locations and uses. Of the 179 bacterial isolates studied, only 11 genera and 15 species were identified using fatty acid methyl ester (FAME) analysis, with culture independent analyses by 16S rDNA denaturing gradient gel electrophoresis (DGGE) and fluorescent in situ hybridization being congruent with these FAME data. In order to gain some insight into functional role of detected populations, we correlated the MWF chemical composition and potential pollution load with bacterial abundance and community composition detected within samples.
The synthesis of the UV‐screening pigment, scytonemin, and photosynthetic performance in isolates from closely related natural populations of cyanobacteria (Calothrix sp.)
Authors: Dillon Jesse G. , Castenholz Richard W.
Published: May 2003

Two populations of the cyanobacterium Calothrix sp. found in Yellowstone thermal spring outflows differ greatly in their contents of scytonemin, a UV‐screening pigment, and in their photosynthetic carbon assimilation rates. Clonal isolates from both populations were used to investigate these phenotypic differences. Identical partial 16S rDNA sequences (∼900 bp) suggest a very close relationship between the two Calothrix populations and indicate that environmental differences may, in part, explain the field observations. The effects of native spring water on scytonemin synthesis and photosynthesis were tested during experiments using plated cells. Results show differences in the spring water environment were at least partly responsible for the differences in scytonemin content observed in the field. Furthermore, spring water effects on photosynthetic performance suggest adaptation in these strains to their spring of origin. Controlled experiments performed using cultures grown in artificial liquid medium showed no significant difference in photosynthetic carbon uptake between strains. However, significant differences were detected in their ability to synthesize scytonemin indicating genetic differences between populations. These findings suggest that both genetic and environmental differences are responsible for the naturally occurring variation in scytonemin content and photosynthetic ability in these two closely related populations.
P-selectin Glycoprotein Ligand-1 Mediates L-Selectin–dependent Leukocyte Rolling in Venules
Authors: Sperandio Markus , Smith Michael L. , Forlow S. Bradley , Olson Timothy S. , Xia Lijun , McEver Rodger P. , Ley Klaus
Published: May 2003

Leukocyte rolling in postcapillary venules of inflamed tissues is reduced in L-selectin–deficient mice and mice treated with L-selectin blocking antibodies, but the glycoprotein ligand for L-selectin in inflamed venules is unknown. Here, we show that L-selectin–dependent rolling after P-selectin blockade is completely absent in P-selectin glycoprotein ligand-1 (PSGL-1)−/− mice or wild-type mice treated with a PSGL-1 blocking monoclonal antibody. Immunohistochemistry and flow cytometry failed to show PSGL-1 expression on resting or inflamed endothelium or on platelets. To investigate whether leukocyte-expressed PSGL-1 is mediating L-selectin–dependent rolling, we reconstituted lethally irradiated wild-type mice with PSGL-1−/− bone marrow cells. These chimeric mice showed no L-selectin–dependent rolling, suggesting that leukocyte-expressed PSGL-1 mediates L-selectin–dependent rolling. Frame-to-frame video analysis of L-selectin–dependent rolling in wild-type mice showed that the majority of observed L-selectin–dependent leukocyte rolling was between free flowing leukocytes and already adherent leukocytes or possibly leukocyte fragments, followed by E-selectin–dependent leukocyte rolling along the endothelium. Leukocyte rolling was significantly slower for leukocyte–endothelial than leukocyte–leukocyte interactions. We conclude that leukocyte-expressed PSGL-1 serves as the main L-selectin ligand in inflamed postcapillary venules. L-selectin binding to PSGL-1 initiates tethering events that enable L-selectin–independent leukocyte-endothelial interactions. These findings provide a molecular mechanism for the inflammatory defects seen in L-selectin–deficient mice.
A New Type of Metal Recognition by Human T Cells
Authors: Gamerdinger Katharina , Moulon Corinne , Karp David R. , van Bergen Jeroen , Koning Frits , Wild Doris , Pflugfelder Ulrike , Weltzien Hans Ulrich
Published: May 2003

In spite of high frequencies of metal allergies, the structural basis for major histocompatibility complex (MHC)-restricted metal recognition is among the unanswered questions in the field of T cell activation. For the human T cell clone SE9, we have identified potential Ni contact sites in the T cell receptor (TCR) and the restricting human histocompatibility leukocyte antigen (HLA)-DR structure. The specificity of this HLA-DR–promiscuous VA22/VB17+ TCR is primarily harbored in its α chain. Ni reactivity is neither dependent on protein processing in antigen-presenting cells nor affected by the nature of HLA-DR–associated peptides. However, SE9 activation by Ni crucially depends on Tyr29 in CDR1α, an N-nucleotide–encoded Tyr94 in CDR3α, and a conserved His81 in the HLA-DR β chain. These data indicate that labile, nonactivating complexes between the SE9 TCR and most HLA-DR/peptide conjugates might supply sterically optimized coordination sites for Ni ions, three of which were identified in this study. In such complexes Ni may effectively bridge the TCR α chain to His81 of most DR molecules. Thus, in analogy to superantigens, Ni may directly link TCR and MHC in a peptide-independent manner. However, unlike superantigens, Ni requires idiotypic, i.e., CDR3α-determined TCR amino acids. This new type of TCR–MHC linkage might explain the high frequency of Ni-reactive T cells in the human population.
Aberrant Chemokine Receptor Expression and Chemokine Production by Langerhans Cells Underlies the Pathogenesis of Langerhans Cell Histiocytosis
Authors: Annels Nicola E. , da Costa Cristiana E.T. , Prins Frans A. , Willemze Annemieke , Hogendoorn Pancras C.W. , Egeler R. Maarten
Published: May 2003

Langerhans cell histiocytosis (LCH) is characterized by a clonal proliferation and retention of cells with a Langerhans cell (LC)-like phenotype at various sites within the body. The present study set out to elucidate whether aberrant expression of chemokine receptors or dysregulation of chemokine production in LCH lesions could explain abnormal retention of these cells. Immunohistochemical analysis on 13 LCH biopsies of bone, skin, and lymph node all expressed the immature dendritic cell (DC) marker CCR6 on the lesional LCs and absence of the mature DC marker CCR7. Furthermore, regardless of the tissue site, LCH lesions markedly overexpressed CCL20/MIP-3α, the ligand for CCR6. The lesional LCs appeared to be the source of this CCL20/MIP-3α production as well as other inflammatory chemokines such as CCL5/RANTES and CXCL11/I-TAC. These may explain the recruitment of eosinophils and CD4+CD45RO+ T cells commonly found in LCH lesions. The findings of this study emphasize that, despite abundant TNF-α, lesional LCs remain in an immature state and are induced to produce chemokines, which via autocrine and paracrine mechanisms cause not only the retention of the lesional LCs but also the recruitment and retention of other lesional cells. We postulate that the lesional LCs themselves control the persistence and progression of LCH.
A role for a novel ‘trans-pseudoknot’ RNA–RNA interaction in the functional dimerization of human telomerase
Authors: Ly Hinh , Xu Lifeng , Rivera Melissa A. , Parslow Tristram G. , Blackburn Elizabeth H.
Published: May 2003

The integral RNA (hTER) of the human telomerase ribonucleoprotein has a conserved secondary structure that contains a potential pseudoknot. Here we examine the role of an intermolecular hTER–hTER interaction in the previously reported functional dimerization of telomerase. We provide evidence that the two conserved, complementary sequences of one stem of the hTER pseudoknot domain can pair intermolecularly in vitro, and that formation of this stem as part of a novel “trans-pseudoknot” is required for telomerase to be active in its dimeric form. Such RNA–RNA interaction mirrors a known property of retroviral reverse transcriptases, which use homodimeric viral genomic RNA substrates.
The master regulator for entry into sporulation inBacillus subtilisbecomes a cell-specific transcription factor after asymmetric division
Authors: Fujita Masaya , Losick Richard
Published: May 2003

Gene transcription at the onset of sporulation inBacillus subtilisis governed by Spo0A, a member of the response regulator family of transcription factors. Spo0A is traditionally viewed as the master regulator for entry into development. We now report that Spo0A continues to function after the initiation phase of sporulation and that it becomes a cell-specific transcription factor when the sporangium is divided into a mother cell and forespore. We observed that (1) Spo0A and Spo0A-directed gene transcription reached high levels in the mother cell; (2) an activated form of Spo0A impaired sporulation when produced in the forespore but not when produced in the mother cell; and (3) an inhibitor of Spo0A called Spo0A-N impaired sporulation and Spo0A-directed transcription when produced in the mother cell but not when produced in the forespore. Spo0A-N, which corresponds to the NH2-terminal domain of Spo0A, was shown to compete with the full-length response regulator for phosphorylation by the phosphorelay protein Spo0B. We propose that Spo0A is the earliest-acting transcription factor in the mother-cell line of gene expression and that in terms of abundance and transcriptional activity Spo0A may function predominantly as a cell-specific regulatory protein.
Likelihood analysis of a first‐order autoregressive model with exponential innovations
Authors: Nielsen B. , Shephard N.
Published: May 2003

Abstract.This paper derives the exact distribution of the maximum likelihood estimator of a first‐order linear autoregression with an exponential disturbance term. We also show that, even if the process is stationary, the estimator isT‐consistent, whereTis the sample size. In the unit root case, the estimator isT2‐consistent, while, in the explosive case, the estimator isρT‐consistent. Further, the likelihood ratio test statistic for a simple hypothesis on the autoregressive parameter is asymptotically uniform for all values of the parameter.
Uncertainty and Economic Sociology:
Authors: Dequech David
Published: May 2003

ABSTRACT. The paper discusses the role of uncertainty in economic sociology, aiming to clarify some controversial issues in the related literature. Initially, some conceptual remarks are made about the relation between economic sociology, neoclassical economics, and rational choice theory. Next, in light of the existing literature on uncertainty and economic sociology, we distinguish between complexity and different types of uncertainty. We also identify different versions of the maximization hypothesis and examine their relations to the different types of uncertainty. Then we defend a concept of fundamental uncertainty that emphasizes the role of institutions. A theory that combines fundamental uncertainty and institutions should emphasize not only the existence of behavior in accordance with institutions, but also the possibility of creative, bold, unconventional behavior, discussed next, as people may use the knowledge provided by institutions to go against the tide. Finally, we suggest that the primary distinction should be that between approaches to economic issues, not between disciplines.
The Merchant and Mr. Reagan:
Authors: Karstensson Lewis
Published: May 2003

ABSTRACT. This paper brings to note for the historical record a facet of Reaganomics with a mercantilist hue. In particular, it is an examination of President Ronald Reagan's 1985 speech, “U.S. Trade Policy: Free and Fair Trade,” President Reagan's major statement on trade policy. The address is shown to have been largely a retaliatory mercantilist tract.
Comments on Warren Samuels's “Why the Georgist Movement Has Not Succeeded”
Authors: Heavey Jerome F.
Published: May 2003

ABSTRACT. The 16th Amendment and the formation of the European Union were major political/economic reforms that should be seen as affirmations of the fundamental principles and teachings of Henry George. That these are not matters of interest to the self‐defined Georgist movement reveals an excessively narrow focus of that movement and suggests its members’ unfamiliarity with much of George's teachings.
Local Government and the Politics of Decency*
Authors: Sharp Elaine B.
Published: May 2003

Objective.Local government officials exhibit a variety of responses to morality issues involving “decency” (i.e., pornography, prostitution, sexually explicit businesses). The purpose of this research is to account for these differences.

Methods.This research analyzes a subset of data from a larger study of morality policy making at the local level, that is, all cases of decision making on decency issues (e.g., pornography, prostitution, regulation of sexually explicit businesses, etc.) that occurred in the period 1994–2000 in 10 of the 52 largest cities in the United States.

Results.In mayoral settings, decision making on decency cases is likely to evoke pro‐decency action from officials when a high level of issue salience is combined with high levels of church adherence, low levels of women's political empowerment, low levels of fundamentalist religious attachment, and higher levels of per capita income. Officials in city manager settings act more favorably toward decency activists if (1) higher levels of salience combine with a lower prevalence of fundamentalist religious adherents and higher levels of per capita income or (2) there is an interaction of salience and low levels of female political empowerment and high unemployment.

Conclusions.Although exploratory in nature, the results confirm conventional expectations concerning the importance of salience and the prevalence of church affiliation; the results are counterintuitive with respect to the prevalence of fundamentalist forces and the extent of female political empowerment.
The Contours and Sources of Ethnic Identity Choices Among Asian Americans*
Authors: Lien Pei‐te , Margaret Conway M. , Wong Janelle
Published: May 2003

Objective. How do individuals of Asian descent in the United States identify themselves in ethnic terms and why? The purpose of this research is to map the contours of ethnic self‐identities among Asian adults and explain their identity preferences in this immigrant community of color.

Methods. We analyze a new and large‐scale survey that collected public opinion from randomly selected individuals of the six largest Asian American descents who resided in five major metropolitan areas in 2000–2001.

Results. We find that two‐thirds of the respondents prefer to identify themselves in ethnic‐specific modes. Although only one in six respondents preferred to identify themselves as “Asian American,” close to six in ten respondents indicated acceptance to this panethnic term as part of their identification. Using multinomial regression analysis, we show that indicators of primordial ties and prior socialization, in addition to cultural, social, and political integration, are instrumental in structuring ethnic identity preferences among Asian Americans.

Conclusions. Our results confirm ethnic identity as a fluid, malleable, and layered phenomenon that depends on context. Our findings also highlight the need for reconsideration and expansion of the extant conceptual frameworks on studying ethnic identity formation for a nonwhite, multiethnic, multilingual, and globally connected population.
Attenuation of
Mycobacterium tuberculosis
by Disruption of a
mas
-Like Gene or a Chalcone Synthase-Like Gene, Which Causes Deficiency in Dimycocerosyl Phthiocerol Synthesis
Authors: Sirakova Tatiana D. , Dubey Vinod S. , Cynamon Michael H. , Kolattukudy Pappachan E.
Published: May 2003

Tuberculosis is one of the leading preventable causes of death. Emergence of drug-resistant tuberculosis makes the discovery of new targets for antimycobacterial drugs critical. The unique mycobacterial cell wall lipids are known to play an important role in pathogenesis, and therefore the genes responsible for their biosynthesis offer potential new targets. To assess the possible role of some of the genes potentially involved in cell wall lipid synthesis, we disrupted a
mas
-like gene,
msl7
, and a chalcone synthase-like gene,
pks10
, with phage-mediated delivery of the disruption construct, in which the target gene was disrupted by replacement of an internal segment with the hygromycin resistance gene (
hyg
). Gene disruption by allelic exchange in the case of each disruptant was confirmed by PCR and Southern blot analyses. Neither
msl7
nor
pks10
mutants could produce dimycocerosyl phthiocerol, although both could produce mycocerosic acids. Thus, it is concluded that these gene products are involved in the biosynthesis of phthiocerol. Both mutants were found to be attenuated in a murine model, supporting the hypothesis that dimycocerosyl phthiocerol is a virulence factor and thus the many steps involved in its biosynthesis offer potential novel targets for antimycobacterial therapy.
Roles of DegP in Prevention of Protein Misfolding in the Periplasm upon Overexpression of Penicillin Acylase in
Escherichia coli
Authors: Pan Kao-Lu , Hsiao Hsu-Chou , Weng Chiao-Ling , Wu Ming-Sheng , Chou C. Perry
Published: May 2003

Enhancement of the production of soluble recombinant penicillin acylase in
Escherichia coli
via coexpression of a periplasmic protease/chaperone, DegP, was demonstrated. Coexpression of DegP resulted in a shift of in vivo penicillin acylase (PAC) synthesis flux from the nonproductive pathway to the productive one when
pac
was overexpressed. The number of inclusion bodies, which consist primarily of protein aggregates of PAC precursors in the periplasm, was highly reduced, and the specific PAC activity was highly increased. DegP was a heat shock protein induced in response to
pac
overexpression, suggesting that the protein could possibly suppress the physiological toxicity caused by
pac
overexpression. Coexpression of DegP
S210A
, a DegP mutant without protease activity but retaining chaperone activity, could not suppress the physiological toxicity, suggesting that DegP protease activity was primarily responsible for the suppression, possibly by degradation of abnormal proteins when
pac
was overexpressed. However, a shortage of periplasmic protease activity was not the only reason for the deterioration in culture performance upon
pac
overexpression because coexpression of a DegP-homologous periplasmic protease, DegQ or DegS, could not suppress the physiological toxicity. The chaperone activity of DegP is proposed to be another possible factor contributing to the suppression.
Leucines 193 and 194 at the N-Terminal Domain of the XylS Protein, the Positive Transcriptional Regulator of the TOL
meta
-Cleavage Pathway, Are Involved in Dimerization
Authors: Ruíz Raquel , Marqués Silvia , Ramos Juan L.
Published: May 2003

Members of the AraC/XylS family of transcriptional regulators are usually organized in two domains: a conserved domain made up of 100 amino acids and frequently located at the C-terminal end, involved in DNA binding; and an N-terminal nonconserved domain involved in signal recognition, as is the case for regulators involved in the control of carbon metabolism (R. Tobes and J. L. Ramos, Nucleic Acids Res.
30:
318-321, 2002). The XylS protein, which is extremely insoluble, controls expression of the
meta
-cleavage pathway for alkylbenzoate metabolism. We fused the N-terminal end of XylS to the maltose-binding protein (MBP) in vitro and found in glutaraldehyde cross-linking assays that the protein dimerized. Experiments with a chimeric N-terminal XylS linked to a ′LexA protein showed that the dimer was stabilized in the presence of alkylbenzoates. Sequence alignments with AraC and UreR allowed us to identify three residues, Leu193, Leu194, and Ile205, as potentially being involved in dimerization. Site-directed mutagenesis of XylS in which each of the above residues was replaced with Ala revealed that Leu193 and Leu194 were critical for activity and that a chimera in which LexA was linked to the N terminus of XylSLeu193Ala or XylSLeu194Ala was not functional. Dimerization of the chimeras MBP-N-XylSLeu193Ala and MBP-N-XylSLeu194Ala was not observed in cross-linking assays with glutaraldehyde.
Characterization of the Double-Partitioning Modules of R27: Correlating Plasmid Stability with Plasmid Localization
Authors: Lawley Trevor D. , Taylor Diane E.
Published: May 2003

Plasmid R27 contains two independent partitioning modules, designated Par1 and Par2, within transfer region 2. Par1 is member of the type I partitioning family (Walker-type ATPase), and Par2 is a member of the type II partitioning family (actin-type ATPase). Stability tests of cloned Par1 and Par2 and insertional disruptions of Par1 and Par2 within R27 demonstrated that Par1 is the major stability determinant whereas Par2 is the minor stability determinant. Creation of double-partitioning mutants resulted in R27 integrating into the chromosome, suggesting that at least one partitioning module is required for R27 to exist in the extrachromosomal form. Using thelacO/LacI-green fluorescent protein (GFP) system, we labeled and visualized R27 and R27 partitioning mutants (Par1−and Par2−) under different growth conditions in liveEscherichia colicells. Plasmid R27 was visualized as the discrete GFP foci present at the mid- and quarter-cell regions in >99% of the cells. Time lapse experiments demonstrated that an increase in R27 plasmid foci resulted from focus duplication in either the mid- or quarter-cell regions ofE. coli. Both R27 Par−variants gave a high percentage of plasmidless cells, as suggested by a uniform GFP signal, and cells with GFP patterns scattered throughout the entire cell, suggesting that plasmid molecules are randomly distributed throughout the cytoplasm. Those cells that did contain R27 Par−with one or two discrete foci had localization patterns that were statistically different from those formed with wild-type R27. Therefore, these results suggest that partitioning-impaired plasmids are characterized by individual and clustered plasmids that are randomly located within the host cytoplasm.
Cell-Cycle-Regulated Expression and Subcellular Localization of theCaulobacter crescentusSMC Chromosome Structural Protein
Authors: Jensen Rasmus B. , Shapiro Lucy
Published: May 2003

Structural maintenance of chromosomes proteins (SMCs) bind to DNA and function to ensure proper chromosome organization in both eukaryotes and bacteria.Caulobacter crescentuspossesses a single SMC homolog that plays a role in organizing and segregating daughter chromosomes. Approximately 1,500 to 2,000 SMC molecules are present per cell during active growth, corresponding to one SMC complex per 6,000 to 8,000 bp of chromosomal DNA. Although transcription from thesmcpromoter is induced during early S phase, a cell cycle transcription pattern previously observed with multiple DNA replication and repair genes, the SMC protein is present throughout the entire cell cycle. Examination of the intracellular location of SMC showed that in swarmer cells, which do not replicate DNA, the protein forms two or three foci. Stalked cells, which are actively engaged in DNA replication, have three or four SMC foci per cell. The SMC foci appear randomly distributed in the cell. Many predivisional cells have bright polar SMC foci, which are lost upon cell division. Thus, chromosome compaction likely involves dynamic aggregates of SMC bound to DNA. The aggregation pattern changes as a function of the cell cycle both during and upon completion of chromosome replication.
The
Escherichia coli
Fis Protein Stimulates Bacteriophage λ Integrative Recombination In Vitro
Authors: Esposito Dominic , Gerard Gary F.
Published: May 2003

The
Escherichia coli
nucleoid-associated protein Fis was previously shown to be involved in bacteriophage lambda site-specific recombination in vivo, enhancing the levels of both integrative recombination and excisive recombination. While purified Fis protein was shown to stimulate in vitro excision, Fis appeared to have no effect on in vitro integration reactions even though a 15-fold drop in lysogenization frequency had previously been observed in
fis
mutants. We demonstrate here that
E. coli
Fis protein does stimulate integrative lambda recombination in vitro but only under specific conditions which likely mimic natural in vivo recombination more closely than the standard conditions used in vitro. In the presence of suboptimal concentrations of Int protein, Fis stimulates the rate of integrative recombination significantly. In addition, Fis enhances the recombination of substrates with nonstandard topologies which may be more relevant to the process of in vivo phage lambda recombination. These data support the hypothesis that Fis may play an essential role in lambda recombination in the host cell.
Identification ofrocA, a Positive Regulator ofcovRExpression in the Group A Streptococcus
Authors: Biswas Indranil , Scott June R.
Published: May 2003

In the group A streptococcus (GAS;Streptococcuspyogenes), a two-component system known as CovRS (or CsrRS) regulates about 15% of the genes, including several important virulence factors like the hyaluronic acid capsule. Most of these genes, includingcovRitself, are negatively regulated by CovR. We have isolated two independent ISS1insertions in an open reading frame (ORF) that increases CovR expression as measured by a Pcov-gusAreporter fusion in single copy in the GAS chromosome. This ORF, namedrocAfor “regulator of Cov,” activatescovRtranscription about threefold. As expected, arocAmutant is mucoid and produces more transcript from thehaspromoter since this promoter is repressed by CovR. This effect is dependent on the presence of a wild-typecovRgene. In contrast to its activation of Pcov, RocA negatively regulates its own expression. This autoregulation is not dependent on the presence of thecovRgene. All the phenotypes of therocAmutant were complemented by the presence of therocAgene on a plasmid. TherocAgene is present in strains of all nine M serotypes of GAS tested and is absent from strains representing 11 other groups of streptococci and related bacteria, including strains of the closely related group C and G streptococci. It seems likely thatrocAplays an important role in the pathogenesis of GAS since it affects expression of the global regulator CovR.
PaeX, a Second Pectin Acetylesterase ofErwinia chrysanthemi3937
Authors: Shevchik Vladimir E. , Hugouvieux-Cotte-Pattat Nicole
Published: May 2003

Erwinia chrysanthemicauses soft-rot diseases of various plants by enzymatic degradation of the pectin in plant cell walls. Pectin is a complex polysaccharide. The main chain is constituted of galacturonate residues, and some of them are modified by methyl and/or acetyl esterification. Esterases are necessary to remove these modifications and, thus, to facilitate the further degradation of the polysaccharidic chain. In addition to PaeY, the first pectin acetylesterase identified in theE.chrysanthemistrain 3937, we showed that this bacterium produces a second pectin acetylesterase encoded by the genepaeX. ThepaeXopen reading frame encodes a 322-residue precursor protein of 34,940 Da, including a 21-amino-acid signal peptide. Analysis ofpaeXtranscription, by using gene fusions, revealed that it is induced by pectic catabolic products and affected by catabolite repression. The expression ofpaeXis regulated by the repressor KdgR, which controls all the steps of pectin catabolism; by the repressor PecS, which controls most of the pectinase genes; and by catabolite regulatory protein, the global activator of sugar catabolism. ThepaeXgene is situated in a cluster of genes involved in the catabolism and transport of pectic oligomers. In induced conditions, the two contiguous geneskdgM, encoding an oligogalacturonate-specific porin, andpaeXare both transcribed as an operon from a promoter proximal tokdgM, but transcription ofpaeXcan also be uncoupled from that ofkdgMin noninduced conditions. PaeX is homologous to the C-terminal domain of theButyrivibrio fibriosolvensxylanase XynB and to a few bacterial esterases. PaeX contains the typical box (GxSxG) corresponding to the active site of the large family of serine hydrolases. Purified PaeX releases acetate from various synthetic substrates and from sugar beet pectin. The PaeX activity increased after previous depolymerization and demethylation of pectin, indicating that its preferred substrates are nonmethylated oligogalacturonides. PaeX is mostly found in the periplasmic space ofE.chrysanthemi. These data suggest that PaeX is mainly involved in the deacetylation of esterified oligogalacturonides that enter the periplasm by the KdgM porin.
Swarm-Cell Differentiation in
Salmonella
enterica
Serovar Typhimurium Results in Elevated Resistance to Multiple Antibiotics
Authors: Kim Wook , Killam Teresa , Sood Vandana , Surette Michael G.
Published: May 2003

Although a wealth of knowledge exists about the molecular and biochemical mechanisms governing the swimming motility of
Salmonella
enterica
serovar Typhimurium, its surface swarming behavior has not been extensively characterized. When inoculated onto a semisolid agar medium supplemented with appropriate nutrients, serovar Typhimurium undergoes a morphological differentiation whereby single cells hyperflagellate and elongate into nonseptate, multinucleate swarm cells. Swarm migration is a collective behavior of groups of cells. We have isolated a
Mu
dJ insertion mutant of serovar Typhimurium 14028 that failed to swarm under any conditions. The site of the
Mu
dJ insertion was determined to be in the
pmrK
locus within the
pmrHFIJKLM
operon, which was previously demonstrated to confer resistance to cationic antimicrobial peptides. β-Galactosidase assays, using the
pmrK
::
lacZ
transcriptional fusion, showed increased expression of the
pmr
operon in swarm cells compared to that in vegetative cells. In concurrence with the expression data, swarm cells exhibited greater tolerance to polymyxin. To compare the profiles of vegetative and swarm-cell resistance to other antibiotics, E-test strips representing a wide range of antibiotic classes were used. Swarm cells exhibited elevated resistance to a variety of antibiotics, including those that target the cell envelope, protein translation, DNA replication, and transcription. These observations, in addition to the dramatic morphological changes associated with the swarming phenotype, provide an intriguing model for examining global differences between the physiological states of vegetative and swarm cells of serovar Typhimurium.
Global Stage-Specific Gene Regulation during the Developmental Cycle of
Chlamydia trachomatis
Authors: Nicholson Tracy L. , Olinger Lynn , Chong Kimberley , Schoolnik Gary , Stephens Richard S.
Published: May 2003

Distinct morphological changes associated with the complex development cycle of the obligate intracellular bacterial pathogen
Chlamydia trachomatis
have been historically well characterized by microscopy. A number of temporally regulated genes have been characterized previously, suggesting that the chlamydial developmental cycle is regulated at the transcriptional level. This hypothesis was tested by microarray analysis in which the entire
C. trachomatis
genome was analyzed, providing a comprehensive assessment of global gene regulation throughout the chlamydial developmental cycle. Seven temporally cohesive gene clusters were identified, with 22% (189 genes) of the genome differentially expressed during the developmental cycle. The correlation of these gene clusters with hallmark morphological events of the chlamydial developmental cycle suggests three global stage-specific networks of gene regulation.
Identification of the
l
-Aspartate Transporter in
Bacillus subtilis
Authors: Lorca Graciela , Winnen Brit , Saier Milton H.
Published: May 2003

YveA of
Bacillus subtilis
, a putative transporter of the amino acid/polyamine/organocation (APC) superfamily, is shown to mediate uptake of both
l
-aspartate and
l
-glutamate as well as having sensitivity to
l
-aspartate hydroxamate. This 14 TMS protein is the primary aspartate uptake system in
B. subtilis
and serves as the prototype for a new family within the APC superfamily.
Differential Expression of the Components of the Two Alkane Hydroxylases from
Pseudomonas aeruginosa
Authors: Marín Mercedes M. , Yuste Luis , Rojo Fernando
Published: May 2003

Oxidation of
n
-alkanes in bacteria is normally initiated by an enzyme system formed by a membrane-bound alkane hydroxylase and two soluble proteins, rubredoxin and rubredoxin reductase.
Pseudomonas aeruginosa
strains PAO1 and RR1 contain genes encoding two alkane hydroxylases (
alkB1
and
alkB2
), two rubredoxins (
alkG1
and
alkG2
), and a rubredoxin reductase (
alkT
). We have localized the promoters for these genes and analyzed their expression under different conditions. The
alkB1
and
alkB2
genes were preferentially expressed at different moments of the growth phase; expression of
alkB2
was highest during the early exponential phase, while
alkB1
was induced at the late exponential phase, when the growth rate decreased. Both genes were induced by C
10
to C
22
/C
24
alkanes but not by their oxidation derivatives. However, the
alkG1
,
alkG2
, and
alkT
genes were expressed at constant levels in both the absence and presence of alkanes.
The
yggH
Gene of
Escherichia coli
Encodes a tRNA (m
7
G46) Methyltransferase
Authors: De Bie Lara G. S. , Roovers Martine , Oudjama Yamina , Wattiez Ruddy , Tricot Catherine , Stalon Victor , Droogmans Louis , Bujnicki Janusz M.
Published: May 2003

We cloned, expressed, and purified the
Escherichia coli
YggH protein and show that it catalyzes the
S
-adenosyl-
l
-methionine-dependent formation of
N
7
-methylguanosine at position 46 (m
7
G46) in tRNA. Additionally, we generated an
E. coli
strain with a disrupted
yggH
gene and show that the mutant strain lacks tRNA (m
7
G46) methyltransferase activity.
Controlled Initiation of Chromosomal Replication inEscherichia coliRequires Functional Hda Protein
Authors: Camara Johanna Eltz , Skarstad Kirsten , Crooke Elliott
Published: May 2003

Regulatory inactivation of DnaA helps ensure that theEscherichia colichromosome is replicated only once per cell cycle, through accelerated hydrolysis of active replication initiator ATP-DnaA to inactive ADP-DnaA. Analysis ofΔhdastrains revealed that the regulatory inactivation of DnaA component Hda is necessary for maintaining controlled initiation but not for cell growth or viability.
TWO-DIMENSIONAL ELECTRONS IN FIELD EFFECT TRANSISTORS
Authors: SHUR MICHAEL S. , DYAKONOV MICHEL
Published: May 2003

In deep submicron silicon MOSFETs, GaAs-based HEMTs, and in new emerging heterostructure systems, such as AlGaN/GaN, electrons forming a two-dimensional (2D) conducting channel exhibit new interesting effects that might find important device applications. Some of these effects are related to the space dependence of the electron mass. Other effects are linked to a large sheet electron concentration, when electrons behave not as a 2D gas but rather as a 2D electron electron fluid. We consider plasma effects in this fluid and discuss plasma wave electronic devices that rely on these effects. We also discuss the properties of 2D electrons in silicon devices, where plasma effects might also play an important role in deep submicron MOSFETs.