bluuebunny/crossref_metadata_2025_split huggingface dataset:
A conserved mitogen‐activated protein kinase pathway is required for mating in Candida albicans
Authors: Chen Jiangye , Chen Jing , Lane Shelley , Liu Haoping 
Published: March 2003

Summary Candida albicans had been thought to lack a mating process until the recent discovery of a mating type‐like locus and mating between MTLa and MTLα strains. To elucidate the molecular mechanisms that regulate mating in C. albicans, we examined the function of Cph1 and its upstream mitogen‐activated protein (MAP) kinase pathway in mating, as they are homologues of the pheromone‐responsive MAP kinase pathway in Saccharomyces cerevisiae. We found that overexpressing CPH1 in MTLa, but not in MTLa/α strains, induced the transcription of orthologues of S. cerevisiae pheromone‐induced genes and also increased mating efficiency. Furthermore, cph1 and hst7 mutants were completely defective in mating, and cst20 and cek1 mutants showed reduced mating efficiency, as in S. cerevisiae. The partial mating defect in cek1 results from the presence of a functionally redundant MAP kinase, Cek2. CEK2 complemented the mating defect of a fus3 kss1 mutant of S. cerevisiae and was expressed only in MTLa or MTLα, but not in MTLa/α cell types. Moreover, a cek1 cek2 double mutant was completely defective in mating. Our data suggest that the conserved MAP kinase pathway regulates mating in C. albicans. We also observed that C. albicans mating efficiency was greatly affected by medium composition, indicating the potential involvement of nutrient‐sensing pathways in mating in addition to the MAP kinase pathway.
Early targeting of Min proteins to the cell poles in germinated spores of Bacillus subtilis: evidence for division apparatus‐independent recruitment of Min proteins to the division site
Authors: Harry Elizabeth J. , Lewis Peter J. 
Published: March 2003

SummaryThe earliest event in bacterial cell division is the assembly of a tubulin‐like protein, FtsZ, at mid‐cell to form a ring. In rod‐shaped bacteria, the Min system plays an important role in division site placement by inhibiting FtsZ ring formation specifically at the polar regions of the cell. The Min system comprises MinD and MinC, which form an inhibitor complex and, in Bacillus subtilis, DivIVA, which ensures that division is inhibited only in the polar regions. All three proteins localize to the division site at mid‐cell and to cell poles. Their recruitment to the division site is dependent on localization of both ‘early’ and ‘late’ division proteins. We have examined the temporal and spatial localization of DivIVA relative to that of FtsZ during the first and second cell division after germination and outgrowth of B. subtilis spores. We show that, although the FtsZ ring assembles at mid‐cell about halfway through the cell cycle, DivIVA assembles at this site immediately before cell division and persists there during Z‐ring constriction and completion of division. We also show that both DivIVA and MinD localize to the cell poles immediately upon spore germination, well before a Z ring forms at mid‐cell. Furthermore, these proteins were found to be present in mature, dormant spores. These results suggest that targeting of Min proteins to division sites does not depend directly on the assembly of the division apparatus, as suggested previously, and that potential polar division sites are blocked at the earliest possible stage in the cell cycle in germinated spores as a mechanism to ensure that equal‐sized daughter cells are produced upon cell division.
Two different modes of transcription repression of the Escherichia coli acetate operon by IclR
Authors: Yamamoto Kaneyoshi , Ishihama Akira 
Published: March 2003

SummaryIclR is a repressor for the Escherichia coli aceBAK operon, which encodes isocitrate lyase (aceB), malate synthase (aceA) and isocitrate dehydroge‐nase kinase/phosphorylase (aceK) in the glyoxylate bypass. IclR also represses the expression of iclR in an autogenous manner. DNase I footprinting and in vitro transcription assays indicated that IclR binds to an IclR box (−21 to +14), which overlaps the iclR promoter and thus competes with the RNA polymerase for DNA binding, leading to transcription repression. In the case of the aceBAK operon, IclR binds to IclR box II between −52 and −19 of the aceB promoter and interferes with binding of the RNA polymerase to this promoter. A secondary IclR binding site (IclR box I) was identified between −125 and −99 of the aceB promoter. IclR binds to this IclR box I even after formation of the aceB promoter open complex and, moreover, induces disassembly of the open complex, leading to repression of aceB transcription. In parallel, the location of the C‐terminal domain of the RNA polymerase α subunit (αCTD) on DNA is shifted close to the IclR box I, indicating that direct interaction between the αCTD and the IclR box I‐associated IclR caused the repression.
Control of the Salmonella ugd gene by three two‐component regulatory systems
Authors: Mouslim Chakib , Groisman Eduardo A. 
Published: March 2003

SummaryThe Salmonella ugd gene is required for the incorporation of 4‐aminoarabinose in the lipopolysaccharide and resistance to the antibiotic polymyxin B. Transcription of the ugd gene is induced by Fe3+ via the PmrA–PmrB two‐component system and by low Mg2+ in a process that requires the PhoP–PhoQ two‐component system, the PhoP‐activated PmrD protein and the PmrA–PmrB system. Here, we establish that mutation of the tolB gene promotes ugd transcription independently of both the PhoP–PhoQ and PmrA–PmrB systems. This activation is mediated by the RcsC–YojN–RcsB phosphorelay and the RcsA protein, suggesting a role for ugd in capsule synthesis. Binding sites for the RcsB, PmrA and PhoP proteins were identified in the ugd promoter. Although the PmrA–PmrB and RcsC–YojN–RcsB systems promoted ugd transcription independently of the PhoP–PhoQ system under different environmental conditions, ugd expression inside macrophages was strictly dependent on PhoP–PhoQ, suggesting that low Mg2+ is a cue for the intracellular environment.
Modified yeast cells to investigate the coupling of G protein‐coupled receptors to specific G proteins
Authors: Ladds Graham , Davis Kevin , Hillhouse Edward W. , Davey John 
Published: March 2003

SummaryG protein‐coupled receptors (GPCRs) help to regulate the physiology of all the major organ systems. They respond to a multitude of ligands and activate a range of effector proteins to bring about the appropriate cellular response. The choice of effector is largely determined by the interaction of individual GPCRs with different G proteins. Several factors influence this interaction, and a better understanding of the process may enable a more rational approach to identifying compounds that affect particular signalling pathways. A number of systems have been developed for the analysis of GPCRs. All provide useful information, but the genetic amenability and relative simplicity of yeast makes them a particularly attractive option for ligand identification and pharmaceutical screening. Many, but not all, GPCRs are functional in the budding yeast Saccharomyces cerevisiae, and we have developed reporter strains of the fission yeast Schizosaccharomyces pombe as an alternative host. To provide a more generic system for investigating GPCRs, we created a series of yeast–human Gα‐transplants, in which the last five residues at the C‐terminus of the yeast Gα‐subunit are replaced with the corresponding residues from different human G proteins. These enable GPCRs to be coupled to the Sz. pombe signalling machinery so that stimulation with an appropriate ligand induces the expression of a signal‐dependent lacZ reporter gene. We demonstrate the specificity of the system using corticotropin releasing factor (CRF) and CRF‐related peptides on two CRF receptors. We find that different combinations of ligand and receptor activate different Gα‐transplants, and the specificity of the coupling is similar to that in mammalian systems. Thus, CRF signalled through the Gs‐ and Gi‐transplants, consistent with its regulation of adenylate cyclase, and was more active against the CRF‐R1A receptor than against the CRF‐R2B receptor. In contrast, urocortin II and urocortin III were selective for the CRF‐R2B receptors. Furthermore, urocortin, but not CRF, induced signalling through the CRF‐R1A receptor and the Gq‐transplant. This is the first time that human GPCRs have been coupled to the signalling pathway in Sz. pombe, and the strains described in this study will complement the other systems available for studying this important family of receptors.
The transmembrane domains of the sensor kinase KdpD of Escherichia coli are not essential for sensing K+ limitation
Authors: Heermann Ralf , Fohrmann Andy , Altendorf Karlheinz , Jung Kirsten 
Published: March 2003

SummaryThe sensor kinase/response regulator system KdpD/KdpE of Escherichia coli regulates the expression of the kdpFABC operon, which encodes the high affinity K+ transport system KdpFABC. The membrane‐bound sensor kinase KdpD consists of four transmembrane domains, a large cytoplasmic N‐terminal domain and a cytoplasmic C‐terminal transmitter domain. To elucidate the role of the four transmembrane domains, various deletions were introduced in kdpD and the activities of the resulting truncated derivatives of KdpD were determined. A KdpD protein lacking all four transmembrane domains was able to sense low K+ concentrations, whereas at higher K+ concentrations kdpFABC expression was constitutive. These and further results with various truncated KdpD proteins lacking distinct parts of the transmembrane domains or derivatives in which a linker peptide or two transmembrane domains of PutP, the Na+/proline transporter of Escherichia coli, replaced the missing part indicated that the transmembrane domains are not essential for sensing of K+ limitation, but may be important for the correct positioning of the large N‐ and C‐terminal cytoplasmic domains to each other.
The Caulobacter crescentus polar organelle development protein PodJ is differentially localized and is required for polar targeting of the PleC development regulator
Authors: Hinz Aaron J. , Larson David E. , Smith Christopher S. , Brun Yves V. 
Published: March 2003

SummaryRegulation of polar development and cell division in Caulobacter crescentus relies on the dynamic localization of several proteins to cell poles at specific stages of the cell cycle. The polar organelle development protein, PodJ, is required for the synthesis of the adhesive holdfast and pili. Here we show the cell cycle localization of PodJ and describe a novel role for this protein in controlling the dynamic localization of the developmental regulator PleC. In swarmer cells, a short form of PodJ is localized at the flagellated pole. Upon differentiation of the swarmer cell into a stalked cell, full length PodJ is synthesized and localizes to the pole opposite the stalk. In late predivisional cells, full length PodJ is processed into a short form which remains localized at the flagellar pole after cell division and is degraded during swarmer to stalked cell differentiation. Polar localization of the developmental regulator PleC requires the presence of PodJ. In contrast, the polar localization of PodJ is not dependent on the presence of PleC. These results indicate that PodJ is an important determinant for the localization of a major regulator of cell differentiation. Thus, PodJ acts directly or indirectly to target PleC to the incipient swarmer pole, to establish the cellular asymmetry that leads to the synthesis of holdfasts and pili at their proper subcellular location.
PriA supports two distinct pathways for replication restart in UV‐irradiated Escherichia coli cells
Authors: Jaktaji Razieh P. , Lloyd Robert G. 
Published: March 2003

SummaryThe Escherichia coli PriA protein loads the DnaB replicative helicase at branched DNA structures independently of the replication initiator protein, DnaA, and thereby facilitates assembly of functional replisomes at sites removed from oriC. It is therefore a critical factor in the rescue of replication forks stalled at DNA lesions. It is also a DNA helicase. We describe insertions near the 3′ end of priA that interfere with PriA activity. These insertions and the previously described priA300 encoding helicase‐defective PriA K230R are shown to be effective suppressors of the DNA repair defect in recG strains, but substantially reduce the ability of ruv mutants to survive DNA damage. The data presented suggest that PriA helicase in conjunction with RecG can promote direct rescue of stalled forks independently of the recombinational pathway promoted by the combined activities of the RuvABC, RecBCD and RecA proteins, which requires only the primosome assembly activity of PriA to load DnaB at D loops. In cells lacking the helicase activity of PriA, we propose that stalled forks can be redirected to the recombination pathway via a Holliday junction intermediate common to both pathways, thus explaining the resistance of these cells to DNA damage.
Molecular mechanisms of iron uptake in fungi
Authors: Kosman Daniel J. 
Published: March 2003

SummaryFungi, like all free‐living organisms, are in competition for limiting nutrients. In accumulating iron, fungi are faced also with a trace metal whose aqueous and redox chemistry make it both relatively bio‐unavailable and strongly cytotoxic. Successful adaptation to this environmental context has provided fungi with an iron uptake strategy that has three features: it relies on redox cycling to enhance iron bio‐availability and reduce iron cytotoxicity; it includes both high‐ and low‐affinity pathways that are mechanistically distinct; and it is autoregulating so as to maintain intracellular iron homeostasis. Using Saccharomyces cerevisiae as a paradigm, this review summarizes current knowledge about the four pathways by which this yeast accumulates iron. These four pathways include: siderophore iron accumulation; high affinity iron uptake via an iron permease; and two lower affinity uptake pathways through relatively non‐specific divalent metal ion transporters. All of these four pathways are directly or indirectly dependent on the activity of metalloreductase activity expressed extracellularly on the plasma membrane. A variety of experimental and genomics data indicate that this resourcefulness is shared by many, if not most, fungi. On the other hand, while the autoregulation of iron metabolism in Baker's yeast is well‐understood, little is known about the apparent homeostatic mechanisms in these other yeasts and fungi. The integration of these multiple uptake mechanisms and their regulation into over‐all iron homeostasis in yeast concludes this brief review.
F1‐catalysed ATP hydrolysis is required for mitochondrial biogenesis in Saccharomyces cerevisiae growing under conditions where it cannot respire
Authors: Lefebvre‐Legendre Linnka , Balguerie Axelle , Duvezin‐Caubet Stéphane , Giraud Marie‐France , Slonimski Piotr P. , Di Rago Jean‐Paul 
Published: March 2003

SummaryMutant strains of yeast Saccharomyces cerevisiae lacking a functional F1‐ATPase were found to grow very poorly under anaerobic conditions. A single amino acid replacement (K222 > E222) that locally disrupts the adenine nucleotide catalytic site in the β‐F1 subunit was sufficient to compromise anaerobic growth. This mutation also affected growth in aerated conditions when ethidium bromide (an intercalating agent impairing mtDNA propagation) or antimycin (an inhibitor of respiration) was included in the medium. F1‐deficient cells forced to grow in oxygen‐limited conditions were shown to lose their mtDNA completely and to accumulate Hsp60p mainly under its precursor form. Fluorescence microscopy analyses with a modified GFP containing a mitochondrial targeting presequence revealed that aerobically growing F1‐deficient cells stopped importing the GFP when antimycin was added to the medium. Finally, after total inactivation of the catalytic α3β3 subcomplex of F1, mitochondria could no longer be energized by externally added ATP because of either a block in assembly or local disruption of the adenine nucleotide processing site. Altogether these data strengthen the notion that in the absence of respiration, and whether the proton translocating domain (F0) of complex V is present or not, F1‐catalysed hydrolysis of ATP is essential for the occurrence of vital cellular processes depending on the maintenance of an electrochemical potential across the mitochondrial inner membrane.
Cell shape, division and development: the 2002 American Society for Microbiology (ASM) conference on prokaryotic development
Authors: Figge Rainer M. , Gober James W. 
Published: March 2003

SummaryIn the last decade, the use of cytological techniques, together with the analysis of complete genomes, has dramatically advanced our understanding of bacterial development. Work on several well‐developed model systems such as Bacillus subtilis, Caulobacter crescentus, Myxococcus xanthus and Streptomyces spp., has provided us with an in‐depth understanding of processes such as sporulation, multicellular behaviour and the bacterial cell cycle. At the same time, these studies have revolutionized our view of the bacterial cell and shown it to be a highly complex entity with spatial and temporal organization. The recent American Society for Microbiology (ASM) conference on prokaryotic development demonstrated that several laboratories have now started to connect data obtained through functional genomic analysis with subcellular organization, thereby generating three‐dimensional regulatory networks. This meeting report highlights new findings in the field, such as regulation of protein localization during sporulation and the cell cycle, control of cell–cell interaction and the initiation of cell division.
Motility in the Roux‐Y limb after distal gastrectomy: relation to the length of the limb and the afferent duodenojejunal segment – an experimental study
Authors: Blanc‐Louvry I. Le , Ducrotté  , Lemeland  , Metayer  , Denis  , TéniÈre  
Published: March 2003

Following gastrectomy, the longer is a Roux‐Y limb constructed to restore digestive continuity the higher the frequency of postoperative symptoms. The aim of this experimental study was to test how the level of the jejunal transection and the length of the Roux limb affect the motility of the constructed limb and in particular the onset and the propagation of activity fronts (AFs).Three months after a distal Roux‐en‐Y gastrectomy, electromyographic tracings were recorded in six groups of rats grouped according to the level of the transection (20 or 40 cm from the pylorus) and the length of the limb (10, 20 or 30 cm). Animals in which a simple laparotomy or laparotomy + jejunal transection was performed, served as controls.During the interdigestive period, all animals had AFs in the limb which were independent from those recorded in the duodenum. In the limb, the mean time interval between two AFs was shorter (P < 0.01) and more irregular than in controls. An increase in limb length was associated with a lower incidence of completely propagated AFs (P < 0.05) and a higher incidence of irregularly propagated AFs (P < 0.01). When propagation of the AFs was analysed both in the limb and in the jejunum distal to the anastomosis, propagation abnormalities were more frequent. Below the gastrojejunal anastomosis, for an intestinal length of either 20 or 30 cm, the frequency of abnormal AFs was not different when this length was either only a limb or a limb with the 10 cm of distal jejunum below the jejuno‐jejunal anastomosis. Interruption of AFs by a meal was irregular in the limb and more rarely observed in the 30‐cm than in 10‐cm limbs (P < 0.05). Interruption of AFs was shorter than in controls (P < 0.01). In the duodenum and the jejunum proximal to the limb, the interval between AFs was higher than in controls and in the Roux‐Y limbs (P < 0.001). Intraluminal concentrations of bacterial strains were not different in the different types of limb while lactobacillus concentrations and pooled concentrations of bacteria were higher than in controls (P < 0.05). No relationship was found between the incidence of myoelectric abnormalities and intraluminal bacterial concentrations.Increasing the length of a Roux‐Y limb resulted in more frequent disturbances in AFs in the limb but had no significant consequence on the overall rate of abnormal AFs in the jejunum distal to the transection. Motor response to food intake was also reduced. Motor changes were not related to intraluminal bacterial concentrations.
The effect of fentanyl, DNQX and MK‐801 on dorsal horn neurones responsive to colorectal distension in the anaesthetized rat
Authors: Kozlowski C. M. , Bountra C. , Grundy D. 
Published: March 2003

Certain dorsal horn neurones respond in a graded manner to noxious colorectal distension (CRD). Morphine inhibits these responses in the spinalized rat, but the role of excitatory amino acids in baseline visceral nociceptive transmission is less clear. This study examines the effect of the μ‐opiate receptor agonist fentanyl, and the non‐NMDA and NMDA antagonists DNQX and MK‐801, respectively, on such responses to CRD in the sodium pentobarbitone‐anaesthetized rat.Male rats were prepared for extracellular recording from the lumbosacral spinal cord. 90 neurones responsive to CRD, located throughout the dorsal horn, were classified according to their response duration and latency to 60 mmHg distension, as SL‐A (short latency‐abrupt; 59%), SL‐S (short latency‐sustained; 23%), L‐L (long‐latency; 10%) and Inhib (inhibited; 8%). Convergent cutaneous receptive fields were mapped for 79/90 neurones and classified as LT (low threshold), WDR (wide dynamic range) or HT (high threshold). CRD (20–100 mm Hg) elicited graded responses in most neurones.In 6/6 SL‐S neurones, fentanyl (1–8 μg kg–1) dose‐dependently inhibited the response to 60 mm Hg CRD, in a naloxone‐sensitive manner, with an ID50 value (±95% confidence limits) of 2.48 (1.7–3.7) μg kg–1. In 6/6 SL‐A neurones, fentanyl had no significant effect on the response to CRD. DNQX (0.03–3 mg kg–1) produced a dose‐dependent inhibition of the response to CRD in 5/5 SL‐A neurones, with an ID50 value of 0.32 (0.01–41.1) mg kg–1. MK‐801 (0.03–0.3 mg kg–1) had no significant effect on responses to CRD in 6/6 SL‐A neurones.The differential inhibitory effects of fentanyl on two neuronal subtypes may indicate functional differences. In SL‐A neurones AMPA/kainate, but not NMDA receptors are involved in mediating baseline nociceptive neurotransmission.
Periodic colonic motor activity identified by 24‐h pancolonic ambulatory manometry in humans
Authors: Hagger R. , Kumar D. , Benson M. , Grundy A. 
Published: March 2003

Abstract

The pattern of colonic motor activity in healthy humans has not been fully elucidated to date. The aim of this study was to evaluate colorectal motor activity employing 24‐h ambulant pancolonic manometry. Ten healthy volunteers (6F, 4M), aged 19–31 years were studied. Motor activity was measured using two custom‐made silicone coated catheters, each with five solid‐state pressure transducers. No bowel preparation or sedation was used. The study period was 24 h. A total of 232 h of recording was obtained. Sixty‐three high amplitude propagated contractions were observed, median six per 24‐h period. Low‐amplitude colonic contractile activity showed regional and diurnal variations. Frequency of contraction was highest in the right colon [median 5.26 cpm (cycles per minute)], and transverse colon and splenic flexure (median 5.15 cpm). The interval between colonic motor complexes was shortest in the transverse colon and splenic flexure. This study introduces a new technique for the evaluation of colorectal motor activity. Subjects were studied in an ambulant setting in their own environment ensuring that this method of study is as physiological as possible. This study demonstrates that colonic motor activity has two main components: high amplitude propagated contractions and low amplitude colonic contractile activity.