| 1. |
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| 2. |
- Ahuja, Umesh, et al.
(författare)
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Haem-delivery proteins in cytochrome c maturation System II
- 2009
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Ingår i: Molecular Microbiology. - : Wiley. - 1365-2958 .- 0950-382X. ; 73:6, s. 1058-1071
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Tidskriftsartikel (refereegranskat)abstract
- P>Cytochromes of the c-type function on the outer side of the cytoplasmic membrane in bacteria where they also are assembled from apo-cytochrome polypeptide and haem. Two distinctly different systems for cytochrome c maturation are found in bacteria. System I present in Escherichia coli has eight to nine different Ccm proteins. System II is found in Bacillus subtilis and comprises four proteins: CcdA, ResA, ResB and ResC. ResB and ResC are poorly understood polytopic membrane proteins required for cytochrome c synthesis. We have analysed these two B. subtilis proteins produced in E. coli and in the native organism. ResB is shown to bind protohaem IX and haem is found covalently bound to residue Cys-138. Results in B. subtilis suggest that also ResC can bind haem. Our results complement recent findings made with Helicobacter CcsBA supporting the hypothesis that ResBC as a complex translocates haem by attaching it to ResB on the cytoplasmic side of the membrane and then transferring it to an extra-cytoplasmic location in ResC, from where it is made available to the apo-cytochromes.
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| 3. |
- Alao, John Patrick, 1973, et al.
(författare)
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Caffeine stabilizes Cdc25 independently of Rad3 in Schizosaccharomyces pombe contributing to checkpoint override
- 2014
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Ingår i: Molecular Microbiology. - : Wiley. - 0950-382X .- 1365-2958. ; 92:4, s. 777-796
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Tidskriftsartikel (refereegranskat)abstract
- Cdc25 is required for Cdc2 dephosphorylation and is thus essential for cell cycle progression. Checkpoint activation requires dual inhibition of Cdc25 and Cdc2 in a Rad3-dependent manner. Caffeine is believed to override activation of the replication and DNA damage checkpoints by inhibiting Rad3-related proteins in both Schizosaccharomyces pombe and mammalian cells. In this study, we have investigated the impact of caffeine on Cdc25 stability, cell cycle progression and checkpoint override. Caffeine induced Cdc25 accumulation in S.pombe independently of Rad3. Caffeine delayed cell cycle progression under normal conditions but advanced mitosis in cells treated with replication inhibitors and DNA-damaging agents. In the absence of Cdc25, caffeine inhibited cell cycle progression even in the presence of hydroxyurea or phleomycin. Caffeine induces Cdc25 accumulation in S.pombe by suppressing its degradation independently of Rad3. The induction of Cdc25 accumulation was not associated with accelerated progression through mitosis, but rather with delayed progression through cytokinesis. Caffeine-induced Cdc25 accumulation appears to underlie its ability to override cell cycle checkpoints. The impact of Cdc25 accumulation on cell cycle progression is attenuated by Srk1 and Mad2. Together our findings suggest that caffeine overrides checkpoint enforcement by inducing the inappropriate nuclear localization of Cdc25.
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| 4. |
- Alao, John Patrick, 1973, et al.
(författare)
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Hyperosmosis enhances radiation and hydroxyurea resistance of S. pombe checkpoint mutants through the spindle checkpoint and delayed cytokinesis
- 2010
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Ingår i: Molecular Microbiology. - : Wiley. - 0950-382X. ; 77:1, s. 143-157
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Tidskriftsartikel (refereegranskat)abstract
- The DNA damage and stress response pathways interact to regulate cellular responses to genotoxins and environmental stresses. How these pathways interact in Schizosaccharomyces pombe is not well understood. We demonstrate that osmotic stress suppresses the DNA damage sensitivity of checkpoint mutants, and that this occurs through three distinct cell cycle delays. A delay in G2/M is dependent on Srk1. Progression through mitosis is halted by a Mad2-dependent spindle checkpoint. Finally, cytokinesis is impaired by modulating Cdc25 expression. These three delays, imposed by osmotic stress, together compensate for the loss of checkpoint signalling.
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| 5. |
- Alao, John Patrick, 1973, et al.
(författare)
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Rad3 and Sty1 function in S. pombe: an integrated response to DNA damage and environmental stress?
- 2008
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Ingår i: Molecular Microbiology. - : Wiley. - 0950-382X. ; 68, s. 246-254
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Forskningsöversikt (refereegranskat)abstract
- In Schizosaccharomyces pombe, the Ataxia Telangiectasia-mutated (Atm)/Atm and Rad 3 Related (Atr) homologue Rad3 is an essential regulator of the response to DNA damage and stalled replication forks. Rad3 activates the downstream kinases Chk1 and Cds1. These kinases in turn inhibit cell cycle progression by mediating Cdc2 phosphorylation. Studies in both yeast and mammalian cells suggest additional roles for Rad3 in regulating cellular responses to environmental stress. In S. pombe, cellular responses to various environmental stresses are regulated primarily through the stress-activated MAP kinase p38 homologue Sty1. An important function of Sty1 is to drive cells rapidly through mitosis by facilitating the accumulation of Cdc25. Interestingly, Sty1 is activated simultaneously with Rad3 following exposure to UV radiation or ionizing radiation (IR). Similarly, exposure to environmental stresses induces the expression of rad3+, cds1+ and other checkpoint regulator genes. It is currently unclear how the pathways regulated by Sty1 and Rad3 and their opposing effects on mitosis are integrated. Recent studies suggest that Sty1 and Rad3 function together to regulate the expression of several stress response genes following exposure to IR. In this review, we discuss current knowledge on the interaction of Rad3/Atm and Sty1/p38 in regulating cellular responses to environmental stress and DNA damage.
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| 6. |
- Aldick, Thomas, et al.
(författare)
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Vesicular stabilization and activity augmentation of enterohaemorrhagic Escherichia coli haemolysin
- 2009
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Ingår i: Molecular Microbiology. - : Blackwell Publishing. - 0950-382X .- 1365-2958. ; 71:6, s. 1496-508
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Tidskriftsartikel (refereegranskat)abstract
- Haemolysin from enterohaemorrhagic Escherichia coli (EHEC-Hly), a putative EHEC virulence factor, belongs to the RTX (repeat-in-toxin) family whose members rapidly inactivate themselves by self-aggregation. By investigating the status of EHEC-Hly secreted extracellularly, we found the toxin both in a free, soluble form and associated, with high tendency and independently of its acylation status, to outer membrane vesicles (OMVs) extruded by EHEC. We compared the interaction of both toxin forms with erythrocytes using scanning electron microscopy and binding assays. The OMV-associated toxin was substantially (80 times) more stable under physiological conditions than the free EHEC-Hly as demonstrated by prolonged haemolytic activity (half-life time 20 h versus 15 min). The haemolysis was preceded by calcium-dependent binding of OMVs carrying EHEC-Hly to erythrocytes; this binding was mediated by EHEC-Hly. We demonstrate that EHEC-Hly is a biologically active cargo in OMVs with dual roles: a cell-binding protein and a haemolysin. These paired functions produce a biologically potent form of the OMV-associated RTX toxin and augment its potential towards target cells. Our findings provide a general concept for stabilization of RTX toxins and open new insights into the biology of these important virulence factors.
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| 7. |
- Andersson, Dan I., et al.
(författare)
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Biological roles of translesion synthesis DNA polymerases in eubacteria
- 2010
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Ingår i: Molecular Microbiology. - : Wiley. - 0950-382X .- 1365-2958. ; 77:3, s. 540-548
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Forskningsöversikt (refereegranskat)abstract
- Biological systems are strongly selected to maintain the integrity of their genomes by prevention and repair of external and internal DNA damages. However, some types of DNA lesions persist and might block the replication apparatus. The universal existence of specialized translesion synthesis DNA polymerases (TLS polymerases) that can bypass such lesions in DNA implies that replication blockage is a general biological problem. We suggest that the primary function for which translesion synthesis polymerases are selected is to rescue cells from replication arrest at lesions in DNA, a situation that, if not amended, is likely to cause an immediate and severe reduction in cell fitness and survival. We will argue that the mutagenesis observed during translesion synthesis is an unavoidable secondary consequence of this primary function and not, as has been suggested, an evolved mechanism to increase mutation rates in response to various stresses. Finally, we will discuss recent data on additional roles for translesion synthesis polymerases in the formation of spontaneous deletions and in transcription-coupled TLS, where the coupling of transcription to TLS is proposed to allow the rescue of the transcription machinery arrested at DNA lesions.
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| 8. |
- Andersson, K, et al.
(författare)
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YopH of Yersinia pseudotuberculosis interrupts early phosphotyrosine signalling associated with phagocytosis.
- 1996
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Ingår i: Molecular Microbiology. - 0950-382X .- 1365-2958. ; 20:5, s. 1057-69
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Tidskriftsartikel (refereegranskat)abstract
- The PTPase YopH of Yersinia is essential to the ability of these bacteria to block phagocytosis. Wild-type Yersinia pseudotuberculosis, but not the yopH mutant strain, resisted phagocytosis by J774 cells. Ingestion of a yopH mutant was dependent on tyrosine kinase activity. Transcomplementation with wild-type yopH restored the anti-phagocytic effect, whereas introduction of the gene encoding the catalytically inactive yopHC403A was without effect. The PTPase inhibitor orthovanadate impaired the anti-phagocytic effect of the wild-type strain, further demonstrating the importance of bacteria-derived PTPase activity for this event. The ability to resist phagocytosis indicates that the effect of the bacterium is immediately exerted when it becomes associated with the phagocyte. Within 30 s after the onset of infection, wild-type Y. pseudotuberculosis caused a YopH-dependent dephosphorylation of phosphotyrosine proteins in J774 cells. Furthermore, interaction of the cells with phagocytosable strains led to a rapid and transient increase in tyrosine phosphorylation of paxillin and some other proteins, an event dependent on the presence of the bacterial surface-located protein invasin. Co-infection with the phagocytosable strain and the wild-type strain abolished the induction of tyrosine phosphorylation. Taken together, the present findings demonstrate an immediate YopH-mediated dephosphorylation of macrophage phosphotyrosine proteins, suggesting that this PTPase acts by preventing early phagocytosis-linked signalling in the phagocyte.
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| 9. |
- Arnqvist, Anna, et al.
(författare)
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Sigma S-dependent growth-phase induction of the csgBA promoter in Escherichia coli can be achieved in vivo by sigma 70 in the absence of the nucleoid-associated protein H-NS.
- 1994
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Ingår i: Molecular Microbiology. - 0950-382X .- 1365-2958. ; 13:6, s. 1021-32
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Tidskriftsartikel (refereegranskat)abstract
- The stationary-phase-specific sigma factor sigma S (RpoS/KatF) is required for Escherichia coli to induce expression of fibronectin-binding curli organelles upon reaching stationary phase. We show that the csgA gene which encodes the curlin subunit protein belongs to a dicistronic operon, csgBA. The transcriptional start site of csgBA was determined and an AT-rich up-stream activating sequence (UAS) required for transcriptional activation was identified. The pcsgBA promoter is not specific for sigma S since the same promoter sequence can be used by E sigma 70 in vivo in a strain lacking nucleoid-associated protein H-NS and sigma S. Transcription remained growth-phase induced and dependent upon the UAS in such a double mutant. Furthermore, we demonstrate that an additional operon, hdeAB, which is also dependent upon sigma S for transcription, can be transcribed by E sigma 70 in vivo in the absence of H-NS by utilizing the phdeAB promoter. Two other genes known to be under the control of sigma S for expression, bolA and katE, remained transcriptionally silent in the absence of H-NS. It is suggested that a subset of E. coli promoters can be recognized by both E sigma S and E sigma 70 in vivo but H-NS interacting with these sequences prevents formation of successful transcription-initiation complexes with E sigma 70.
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| 10. |
- Arnqvist, Anna, et al.
(författare)
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The Crl protein activates cryptic genes for curli formation and fibronectin binding in Escherichia coli HB101.
- 1992
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Ingår i: Molecular Microbiology. - 0950-382X .- 1365-2958. ; 6:17, s. 2443-52
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Tidskriftsartikel (refereegranskat)abstract
- Curli are thin, coiled, temperature-regulated fibres on fibronectin-binding Escherichia coli. The subunit protein of curli was highly homologous at its amino terminus to SEF-17, the subunit protein of thin, aggregative fimbriae of Salmonella enteritidis 27655 strain 3b, suggesting that these fibres form a novel class of surface organelles on enterobacteria. E. coli HB101 is non-curliated and unable to bind soluble, iodinated fibronectin. The phenotypically cryptic curlin subunit gene, csgA, in HB101 is transcriptionally activated by expressing the cytoplasmic Crl on a multicopy plasmid. Transcriptional activation of csgA by Crl was observed after growth at 26 degrees C but not at 37 degrees C, even though crl transcription was not thermoregulated. A deletion of the 39 carboxy-terminal residues abolished Crl activity, whereas a deletion of 10 residues at the C-terminus did not, implying that a region between residue 93 and 122 in the 132-amino-acid-residue large Crl protein is required for activating curli expression in E. coli HB101. crl is a normal housekeeping gene in E. coli and it is suggested that its gene product may either be a DNA-binding protein affecting chromatin structure as has been suggested for histone-like protein H1 or interact with specific regulatory protein(s) controlling transcription of genes required for curli formation and fibronectin binding.
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