bluuebunny/crossref_metadata_2025_split huggingface dataset:
Ribosomal and non‐ribosomal resistance to oxazolidinones: species‐specific idiosyncrasy of ribosomal alterations
Authors: Sander P. , Belova L. , Kidan Y. G. , Pfister P. , Mankin A. S. , Böttger E. C. 
Published: March 2003

SummaryA derivative of Mycobacterium smegmatis, which carries only one functional rRNA (rrn) operon, was used to isolate mutants resistant to the ribosome‐targeted antibiotic linezolid. Isolation and characterization of linezolid‐resistant clones revealed two classes of mutants. Ribosomes from class I mutants are resistant to oxazolidinones in an in vitro peptidyl transferase assay, indicating that resistance maps to the ribosome component. In contrast, ribosomes from class II mutants show wild‐type susceptibility to a linezolid derivative in vitro, pointing to a non‐ribosomal mechanism of resistance. Introduction of a wild‐type ribosomal RNA operon into linezolid‐resistant strains restored linezolid sensitivity in class I mutants, indicating that resistance (i) maps to the rRNA and (ii) is recessive. Sequencing of the entire rrn operon identified a single nucleotide alteration in 23S rRNA of class I mutant strains, 2447G → T (Escherichia coli numbering). Introduction of mutant rrl2447T into M. smegmatis rrn– resulted in a linezolid‐resistant phenotype, demonstrating a cause–effect relationship of the 2447G → T alteration. The 2447G → T mutation, which renders M. smegmatis linezolid resistant, confers lethality in E. coli. This finding is strong evidence of structural and pos‐sibly functional differences between the ribosomes of Gram‐positive and Gram‐negative bacteria. In agreement with the results of the in vitro assay, class II mutants show a wild‐type sequence of the complete rRNA operon. The lack of cross‐resistance of the class II mutants to other antibiotics suggests a resistance mechanism other than activation of a broad‐spectrum multidrug transporter.
An inhibitor of DNA binding and uptake events dictates the proficiency of genetic transformation in Neisseria gonorrhoeae: mechanism of action and links to Type IV pilus expression
Authors: Aas Finn Erik , Løvold Cecilia , Koomey Michael 
Published: March 2003

SummaryAlthough natural genetic transformation is a widely disseminated form of genetic exchange in prokaryotic species, the proficiencies with which DNA recognition, uptake and processing occur in nature vary greatly. However, the molecular factors and interactions underlying intra‐ and interspecies diversity in levels of competence for natural genetic transformation are poorly understood. In Neisseria gonorrhoeae, the Gram‐negative aetiologic agent of gonorrhoea, DNA binding and uptake involve components required for Type IV pilus (Tfp) biogenesis as well as those which are structurally related to Tfp biogenesis components but dispensable for organelle expression. We demonstrate here that the gonococcal PilV protein, structurally related to Tfp pilin subunits, is an intrinsic inhibitor of natural genetic transformation which acts ultimately by reducing the levels of sequence‐specific DNA uptake into the cell. Specifically, we show that DNA uptake is enhanced in strains bearing pilV mutations and reduced in strains overexpressing PilV. Furthermore, we show that PilV exerts its effect by acting as an antagonist of ComP, a positive effector of sequence‐specific DNA binding. As it prevents the accumulation of ComP at a site where it can be purified by shear extraction of intact cells, the data are most consistent with PilV either obstructing ComP trafficking or altering ComP stability. In addition, we report that ComP and PilV play overlapping and partially redundant roles in Tfp biogenesis and document other genetic interactions between comP and pilV together with the pilE and pilT genes required for the expression of retractile Tfp. Together, the results reveal a novel mechanism by which the levels of competence are governed in prokaryotic species and suggest unique ways by which competence might be modulated.
The requirement of the LC8 dynein light chain for nuclear migration and septum positioning is temperature dependent in Aspergillus nidulans
Authors: Liu Bo , Xiang Xin , Lee Yuh‐Ru Julie 
Published: March 2003

SummaryIn the filamentous fungus Aspergillus nidulans, the multisubunit motor complex cytoplasmic dynein plays essential roles in nuclear migration and septum positioning. The 8 kDa light chain, LC8, the smallest subunit, is conserved among eukaryotic organisms. Besides being a component in the dynein complex, LC8 also interacts with a wide spectrum of mammalian and viral proteins. To date, the function of this small polypeptide is not well understood. To address this issue, we have created a deletion mutation (ΔnudG) at the nudG locus encoding LC8 in A. nidulans. At 42°C, the ΔnudG mutant forms minute colonies lacking asexual reproduction: this phenotype resembles the phenotype of the dynein heavy chain null mutant. The mutant nuclei largely clustered in the spore body after conidial germination, and the septum was often assembled distally toward the hyphal apex, whereas a control germling has its nuclei distributed along the hypha and the septum formed near the spore body. When the mutant was grown at 23°C, however, its colony resembled a control one, and so did the patterns of nuclear distribution and septum positioning. Elevation of the growth temperature gradually reduced colony size and abolished asexual sporulation. After a period of growth at 23°C that allowed the nuclei to move out of the spore end, a temperature shift to 42°C prevented newly divided nuclei from migrating apart, suggesting that LC8/NUDG was required for both initiating and maintaining dynein motor functions at elevated temperatures. A functional GFP‐NUDA fusion was used to test whether LC8/NUDG is required for DHC (dynein heavy chain)/NUDA localization. We found that at 23°C GFP‐NUDA localized to the hyphal apex and the septation site in ΔnudG cells as in control cells. Such localizations were absent at 42°C in mutant cells, but not in control cells. We conclude that LC8 plays a role in DHC localization/function, and the requirement for such a role in A. nidulans cells is temperature dependent.
Siderophore‐mediated cell signalling in Pseudomonas aeruginosa: divergent pathways regulate virulence factor production and siderophore receptor synthesis
Authors: Beare Paul A. , For Raewyn J. , Martin Lois W. , Lamont Iain L. 
Published: March 2003

SummaryUnder iron‐limiting conditions, Pseudomonas aeruginosa produces a siderophore called pyoverdine. Pyoverdine is secreted into the extracellular environment where it chelates iron, and the resulting ferri‐pyoverdine complexes are transported back into the bacteria by a cell surface receptor protein FpvA. Pyoverdine also acts as a signalling molecule inducing the production of three secreted virulence factors. Binding of ferri‐pyoverdine to FpvA transduces a signal to the periplasmic part of the membrane‐spanning antisigma factor FpvR. The signal is transmitted to the cytoplasmic part of FpvR, which controls the activity of an extracytoplasmic family (ECF) sigma factor protein PvdS. This results in the production of the virulence factors pyoverdine, exotoxin A and PrpL endoprotease. Here, we show that a second divergent branch of this signalling pathway regulates the production of the FpvA protein. FpvR negatively regulates the activity of a second ECF sigma factor, FpvI, which is required for the synthesis of FpvA, and the presence of ferri‐pyoverdine greatly increases the activity of FpvI so that production of FpvA is induced. To the best of our knowledge, this is the first example of a branched signalling system of this sort and the first example of an antisigma factor protein (FpvR) that directly regulates the activities of two different ECF sigma factor proteins (PvdS and FpvI).
EFG1 is a major regulator of cell wall dynamics in Candida albicans as revealed by DNA microarrays
Authors: Sohn K. , Urban C. , Brunner H. , Rupp S. 
Published: March 2003

SummaryCell wall dynamics in Candida albicans, the most common fungal pathogen in man, underlie regulatory processes during the yeast‐to‐hyphae transition. To analyse this regulation at the transcriptional level, we have established a DNA microarray representing genes implicated in cell wall biogenesis. Using these microarrays, we were able to identify YWP1 and HWP2 that are specifically transcribed in the yeast or hyphal growth form respectively. Cluster analysis revealed at least two major clusters of genes: cluster I comprised genes that were upregulated under at least one hyphae‐inducing condition. Three as yet not further characterized genes were attributed to cluster II. These genes were transcribed in the yeast form of C. albicans and were downregulated in an EFG1‐dependent manner under specific hyphae‐inducing conditions. We show further that, in contrast to CPH1, EFG1 plays a major role in the transcriptional regulation of cell wall proteins under the conditions investigated. EFG1 was essential for the transcription of both hyphae‐specific genes such as HWP1 and HWP2 as well as the yeast form‐specific gene YWP1. Moreover, we found that, under various conditions, EFG1 also can act as a strong repressor for the transcription of RBE1, another not yet characterized cell wall protein. Overall, our data show that EFG1 plays a major role in the induction and repression of cell wall genes, not only in the hyphal form but also in the yeast form of C. albicans.
Steroid biosynthesis in prokaryotes: identification of myxobacterial steroids and cloning of the first bacterial 2,3(S)‐oxidosqualene cyclase from the myxobacterium Stigmatella aurantiaca
Authors: Bode Helge Björn , Zeggel Bernd , Silakowski Barbara , Wenzel Silke C. , Reichenbach Hans , Müller Rolf 
Published: March 2003

SummarySteroids, such as cholesterol, are synthesized in almost all eukaryotic cells, which use these triterpenoid lipids to control the fluidity and flexibility of their cell membranes. Bacteria rarely synthesize such tetracyclic compounds but frequently replace them with a different class of triterpenoids, the pentacyclic hopanoids. The intriguing mechanisms involved in triterpene biosynthesis have attracted much attention, resulting in extensive studies of squalene‐hopene cyclase in bacteria and (S)‐2,3‐oxidosqualene cyclases in eukarya. Nevertheless, almost nothing is known about steroid biosynthesis in bacteria. Only three steroid‐synthesizing bacterial species have been identified before this study. Here, we report on a variety of sterol‐producing myxobacteria. Stigmatella aurantiaca is shown to produce cycloartenol, the well‐known first cyclization product of steroid biosynthesis in plants and algae. Additionally, we describe the cloning of the first bacterial steroid biosynthesis gene, cas, encoding the cycloartenol synthase (Cas) of S. aurantiaca. Mutants of cas generated via site‐directed mutagenesis do not produce the compound. They show neither growth retardation in comparison with wild type nor any increase in ethanol sensitivity. The protein encoded by cas is most similar to the Cas proteins from several plant species, indicating a close evolutionary relationship between myxobacterial and eukaryotic steroid biosynthesis.
Lack of SeqA focus formation, specific DNA binding and proper protein multimerization in the Escherichia coli sequestration mutant seqA2
Authors: Fossum Solveig , Søreide Sølvi , Skarstad Kirsten 
Published: March 2003

SummaryIn Escherichia coli wild‐type cells newly formed origins cannot be reinitiated. The prevention of reinitiation is termed sequestration and is dependent on the hemimethylated state of newly replicated DNA. Several mutants discovered in a screen for the inability to sequester hemimethylated origins have been mapped to the seqA gene. Here, one of these mutants, seqA2, harbouring a single amino acid change in the C‐terminal end of the SeqA protein, was found to also be unable to form foci in vivo. The SeqA foci seen in the wild‐type cells are believed to arise from multimerization of SeqA on hemimethylated DNA at the replication fork, presumably representing organization of newly formed DNA by SeqA. The result suggests that the process of origin sequestration is closely tied to the process of focus maintenance at the replication fork. In vitro, purified SeqA2 protein was found incapable of forming highly ordered multimers that bind hemimethylated oriC. The mutant protein was also incapable of restraining negative supercoils. Both in vivo and in vitro results support the idea that origin sequestration is an integral part of organization of newly formed DNA performed by SeqA.
A model for evaluation of gastric sensitivity in awake rats
Authors: Rouzade  , Fioramonti  , Bueno  
Published: March 2003

We developed a model for the evaluation of gastric sensitivity to distension in awake rats. A balloon made from a latex condom was chronically placed in the stomach and three stainless steel electrodes were implanted in the neck muscles. Isobaric distensions were performed with a barostat by step of 5 mmHg with 10 min inflation and 2 min deflation. Gastric pressure, integrated neck electromyogram (EMG) and gastric volume were continuously monitored on a potentiometric recorder. Gastric distension at 15 or 20 mmHg induced a typical posture associated with contractions of the neck muscles. Pain threshold was defined as the pressure inducing an increase of integrated neck EMG greater than 100%.The mean pain threshold was 18.5 ± 0.7 mmHg and was not modified 2, 4 and 7 days after the first experiment. However, gastric volumes were significantly higher on the 4th and the 7th days. Morphine at the doses of 0.4 and 4 mg kg−1 i.p. significantly increases the pain threshold. At the doses of 0.04 and 0.4 mg kg−1, morphine significantly increased gastric volume for the distending pressure of 10 mmHg. Naloxone (2.5 mg kg−1 i.p.) reversed the effects of morphine. In conclusion, our model permits simultaneous evaluation of pain threshold and gastric compliance associated with gastric distension in conscious rats.
Influence of age on rectal tone and sensitivity to distension in healthy subjects
Authors: LAGIER  , DELVAUX  , VELLAS  , FIORAMONTI  , BUENO  , ALBAREDE  , FREXINOS  
Published: March 2003

Hypersensitivity to rectal distension is frequently observed in patients with irritable bowel syndrome (IBS). However, few data are available about the influence of age on rectal sensory thresholds and tone. The aim of this study was to measure rectal sensory thresholds and tone with a barostat in 12 healthy subjects (aged 86 ± 4 years, eight females, four males) as compared with 12 young healthy male controls (26 ± 1 years). Isobaric phasic distensions were performed in the fasted state (increment of 4 mmHg, steps of 5 min, interval of 5 min). Rectal tone changes were then measured as changes in volume of the barostat bag, the pressure being kept constant. After a baseline recording of 1 h, a 1000‐kcal meal was served and the tone recorded until return to baseline.Rectal sensory thresholds were significantly higher in aged subjects. First sensation, sensation of urge to defaecate and sensation of pain were triggered at 21.1 ± 3.2 mmHg, 30.4 ± 5.4 mmHg and 40.5 ± 5.0 mmHg, respectively, in aged subjects, vs 13.3 ± 4.6 mmHg (P < 0.05), 20.7 ± 1.0 mmHg (P < 0.001), 31.3 ± 1.7 mmHg (P < 0.001) in controls. Rectal compliance was not significantly different between the two groups. Mean barostat bag volume was 104 ± 13 mL in fasting aged subjects and 125 ± 23 mL in controls (NS). After the meal, the barostat bag volume decreased by 69 ± 11% during 85 ± 17 min in aged subjects and 75 ± 14% during 89 ± 15 min in young controls (NS). Rectal sensory thresholds triggered by distension are increased in aged healthy subjects while compliance and tone are not different. Age should be considered as a confounding factor when studying rectal sensitivity and further studies in aged patients with IBS should include a group of control subjects within the same range of age as studied patients.
Neurogenic pathways mediating ascending and descending reflexes at the porcine ileocolonic junction
Authors: Kajimoto  , Dinning  , Gibb  , De Carle  , Cook  
Published: March 2003

We studied the pharmacology of the neural pathways mediating the responses of ileo‐ and coloileo‐colonic junction (ICJ) to regional distension in ten anaesthetized pigs. Using manometric pullthroughs and a sleeve sensor, we found the ICJ demonstrated sustained tone that was resistant to tetrodotoxin. Ileal distension decreased ICJ pressure by 22.2 ± 10.1% (11.9 ± 2.7–10.1 ± 2.6 mmHg; P=0.002) and colonic distension augmented ICJ pressure by 23.5 ± 8.6% (12.8 ± 1.5–15.6 ± 2.1 mmHg; P=0.02). Bethanecol and Nω‐nitro‐ L‐arginine methyl ester (
L‐NAME) increased ICJ pressure (P=0.002, P=0.01, respectively). Sodium nitroprusside and isoproterenol reduced ICJ pressure (P=0.004, P=0.02, respectively). In the presence of
L‐NAME, the early inhibitory ileo‐ICJ response was abolished, while early and late inhibitory responses were abolished by further addition of propranolol but not by the addition of hexamethonium, atropine, prazosin or yohimbine. The excitatory colo‐ICJ response was replaced by inhibition in the presence of
L‐NAME. We concluded that: 1 the porcine ICJ displays myogenic tone which is influenced by excitatory muscarinic and inhibitory nitrergic and beta adrenergic pathways 2 an inhibitory ileo‐sphincteric reflex mediated by nitrergic and beta adrenergic postganglionic neural pathways 3 both excitatory and inhibitory neurogenic colo‐sphincteric reflexes exist, and the excitatory pathway involves nitrergic neurotransmission.
Distinct regional expression of SNARE proteins in the feline oesophagus
Authors: Ji J. , Lau H. , Sheu L. , Diamant N. E. , Gaisano H. Y. 
Published: March 2003

Abstract
Soluble N‐ethylmaleimide‐sensitive factors attachment protein receptors (SNAREs), initially found to mediate membrane fusion, have now been shown to also bind and regulate a number of membrane ion channels in neurones and neuroendocrine cells. We recently reported that the SNARE protein SNAP‐25 regulates Ca2+‐ activated (KCa) and delays rectifier K+channels (KV) in oesophageal smooth muscle cells. This raised the possibility that cognate and other SNARE proteins could also be present in the oesophageal smooth muscle cell to regulate these and other functions. Circular muscle tissue sections and single freshly isolated muscle cells from the oesophageal body circular and longitudinal layers, and from lower oesophageal sphincter clasp and sling regions were studied. The subcellular location of SNAP‐23, SNAP‐25, syntaxins 1 to 4, and vesicle‐associated membrane protein (VAMP)‐2 were explored using a laser scanning confocal imaging system. Feline oesophageal smooth muscle of all regions examined demonstrated the presence of SNAP‐23, SNAP‐25, syntaxins 1 to 4, and VAMP‐2 on the plasma membrane. The intensity of these syntaxins and SNAP‐25/‐23 proteins varied between the different muscle groups of the oesophagus. In some regions, some SNARE proteins were also noted in the muscle cell cytoplasm. No differential expression was found for VAMP‐2. The differential expression of SNAP‐25 and its regulation of K+channels indicate the important role of SNAP‐25 in regulating the distinct membrane excitability and contractility along the smooth muscle of the oesophagus. This is further contributed by its interactions with the cognate syntaxins, which are also differentially expressed in the muscle groups of the oesophageal body and lower oesophageal sphincter (LOS). These SNARE proteins probably have other functions in the smooth muscle cell, such as regulating vesicular transport processes.
Prion encephalopathy with insertion of octapeptide repeats: the number of repeats determines the type of cerebellar deposits
Authors: Vital C. , Gray F. , Vital A. , Parchi P. , Capellari S. , Petersen R. B. , Ferrer X. , Jarnier D. , Julien J. , Gambetti P. 
Published: March 2003

C. Vital, F. Gray, A. Vital, P. Parchi, S. Capellari, R. B. Petersen, X. Ferrer, D. Jarnier, J. Julien and P. Gambetti (1998) Neuropathology and Applied Neurobiology24, 125–130Prion encephalopathy with insertion of octapeptide repeats: the number of repeats determines the type of cerebellar depositsWe studied modifications of the molecular layer of the cerebellum in three patients with octapeptide repeat insertion (OPRI). Two brothers carrying a six‐OPRI showed only spongiosis in haematoxylin & eosin preparations (H&E), whereas immunocytochemical examination (ICC) with an antiprion protein (PrP) antibody revealed numerous elongated PrP deposits. The third patient from a family with an eight‐OPRI had numerous plaques visible in H&E preparations and had been diagnosed as Gerstmann‐Straüssler–Scheinker syndrome. So far, 15 other cases from seven families and three individual cases with OPRI have undergone neuropathological examination. Characteristic PrP deposits were seen in six other cases, two isolated cases with a four‐ and a seven‐OPRI, whereas four cases with a six‐OPRI came from three different families. Such deposits have never been reported in other cases of prion encephalopathy, without OPRI. Genuine plaques were observed in five out of the 15 other patients. Interestingly, four had an eight‐OPRI and one a nine‐OPRI. Cases with OPRI are prone to develop different PrP deposits: those only visible on ICC are not to be confused with genuine plaques visible in H&E preparations. Elongated PrP deposits are present in cases with a four‐ to seven‐OPRI, whereas plaques are present when there is an eight‐ or a nine‐OPRI. All these cases should be termed prion encephalopathy with OPRI.
Adult survival after prenatal exposure to the Dutch famine 1944–45
Authors: Roseboom T. J. , Meulen J. H. P. van der , Osmond C. , Barker D. J. P. , Ravelli A. C. J. , Bleker O. P. 
Published: March 2003

SummaryEarly life events may affect adult survival. We studied the effect of prenatal exposure to the Dutch famine 1944–45 on survival among 2254 people born in Amsterdam. Mortality up to age 50 was highest among those born before the famine (15.2%) and among those exposed to famine in late gestation (14.6%). It was lower among those exposed in mid‐ (11.2%) or early gestation (11.5%), and was lowest among those conceived after the famine (7.2%). These differences were caused by effects on mortality in the first year after birth and were mainly related to nutrition and infections. There was no effect of exposure to famine on mortality after the age of 18. The hazard ratio was 1.4 [0.8, 2.3] for those born before the famine, 1.1 [0.5, 2.3] for those exposed in late gestation, 0.8 [0.3, 1.8] for those exposed in mid‐gestation and 1.1 [0.5, 2.5] in those exposed in early gestation compared with those conceived after the famine. We could not demonstrate effects of prenatal exposure to famine on cause‐specific mortality after the age of 18. Because prenatal exposure to famine is linked to cardiovascular risk factors and disease, increased cardiovascular mortality in the future may be expected.