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101.
The light receptor and its mode of operation were studied in photosensitive oospores of Nitella furcata subsp. megacarpa (Allen emend. Wood). Brief pulses of light activated maximal germination of post-secondary dormant oospores removed from lake sediments. Fluence response data at 12 wavelengths were used to construct an action spectrum for germination. The shape of the action spectrum with its maximum at 669 nm provides evidence for the involvement of phytochrome. Germination was induced with photon fluences that established as little as 0.01% of the phytochrome in the far red-absorbing form, which suggests that phytochrome was operating in the very low-fluence response mode. The functioning of phytochrome in the very low-fluence response mode in Nitella is similar to that in higher plants. 相似文献
102.
Quorum Sensing in Burkholderia cepacia: Identification of the LuxRI Homologs CepRI 总被引:6,自引:0,他引:6 下载免费PDF全文
Shawn Lewenza Barbara Conway E. P. Greenberg Pamela A. Sokol 《Journal of bacteriology》1999,181(3):748-756
Burkholderia cepacia has emerged as an important pathogen in patients with cystic fibrosis. Many gram-negative pathogens regulate the production of extracellular virulence factors by a cell density-dependent mechanism termed quorum sensing, which involves production of diffusible N-acylated homoserine lactone signal molecules, called autoinducers. Transposon insertion mutants of B. cepacia K56-2 which hyperproduced siderophores on chrome azurol S agar were identified. One mutant, K56-R2, contained an insertion in a luxR homolog that was designated cepR. The flanking DNA region was used to clone the wild-type copy of cepR. Sequence analysis revealed the presence of cepI, a luxI homolog, located 727 bp upstream and divergently transcribed from cepR. A lux box-like sequence was identified upstream of cepI. CepR was 36% identical to Pseudomonas aeruginosa RhlR and 67% identical to SolR of Ralstonia solanacearum. CepI was 38% identical to RhlI and 64% identical to SolI. K56-R2 demonstrated a 67% increase in the production of the siderophore ornibactin, was protease negative on dialyzed brain heart infusion milk agar, and produced 45% less lipase activity in comparison to the parental strain. Complementation of a cepR mutation restored parental levels of ornibactin and protease but not lipase. An N-acylhomoserine lactone was purified from culture fluids and identified as N-octanoylhomoserine lactone. K56-I2, a cepI mutant, was created and shown not to produce N-octanoylhomoserine lactone. K56-I2 hyperproduced ornibactin and did not produce protease. These data suggest both a positive and negative role for cepIR in the regulation of extracellular virulence factor production by B. cepacia. 相似文献
103.
S Y Sokol 《Current opinion in genetics & development》1999,9(4):405-410
The dorso-ventral axis is specified in vertebrates through the formation of a dorsal signaling center known as the Spemann organizer. This process depends on signal transduction by beta-catenin that can be regulated by secreted Wnt proteins. Recent discoveries of new players in this signaling pathway have narrowed down the search for the initial cues for axis specification in vertebrate embryos. 相似文献
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Licorice compounds glycyrrhizin and 18beta-glycyrrhetinic acid are potent modulators of bile acid-induced cytotoxicity in rat hepatocytes 总被引:6,自引:0,他引:6
Gumpricht E Dahl R Devereaux MW Sokol RJ 《The Journal of biological chemistry》2005,280(11):10556-10563
The accumulation of hydrophobic bile acids results in cholestatic liver injury by increasing oxidative stress, mitochondrial dysfunction, and activation of cell signaling pathways. Licorice root and its constituents have been utilized as antihepatotoxic agents. The purpose of this study was to evaluate the potential modulation by a primary component of licorice root, glycyrrhizin (GL), and its metabolite, 18beta-glycyrrhetinic acid (GA), in a hepatocyte model of cholestatic liver injury. Preincubation of fresh rat hepatocyte suspensions with GL or GA reduced glycochenodeoxycholic acid (GCDC)-dependent reactive oxygen species generation, with GA more potent than GL. Interestingly, GL and GA had opposing effects toward GCDC-induced cytotoxicity; GA prevented both necrosis and apoptosis, whereas GL enhanced apoptosis. GCDC promoted activation of caspase 10, caspase 3, and PARP; all were inhibited by GA but not GL. Induction of apoptosis by GCDC was also associated with activation of JNK, which was prevented by GA. Activation of caspase 9 and dissipation of mitochondrial membrane potential were prevented by GA but not GL. In liver mitochondrial studies, GL and GA were both potent inhibitors of the mitochondrial permeability transition, reactive oxygen species generation, and cytochrome c release at submicromolar concentrations. Results from this study suggest that GL exhibits pro-apoptotic properties, whereas GA is a potent inhibitor of bile acid-induced apoptosis and necrosis in a manner consistent with its antioxidative effect. 相似文献
106.
Sokol S 《Nature cell biology》2000,2(7):E124-E125
Recent studies have shown that secreted Wnt proteins control morphogenetic movements in fish and frog embryos. The analysis of Dishevelled, a cytoplasmic mediator of Wnt signalling, reveals unexpected similarity between gastrulation in vertebrates and polarization of cells in Drosophila epithelia. 相似文献
107.
Quorum-sensing mutations affect attachment and stability of Burkholderia cenocepacia biofilms 总被引:1,自引:0,他引:1
Tomlin KL Malott RJ Ramage G Storey DG Sokol PA Ceri H 《Applied and environmental microbiology》2005,71(9):5208-5218
Biofilm formation in Burkholderia cenocepacia has been shown to rely in part on acylhomoserine lactone-based quorum sensing. For many other bacterial species, it appears that both the initial adherence and the later stages of biofilm maturation are affected when quorum sensing pathways are inhibited. In this study, we examined the effects of mutations in the cepIR and cciIR quorum-sensing systems of Burkholderia cenocepacia K56-2 with respect to biofilm attachment and antibiotic resistance. We also examined the role of the cepIR system in biofilm stability and structural development. Using the high-throughput MBEC assay system to produce multiple equivalent biofilms, the biomasses of both the cepI and cepR mutant biofilms, measured by crystal violet staining, were less than half of the value observed for the wild-type strain. Attachment was partially restored upon providing functional gene copies via multicopy expression vectors. Surprisingly, neither the cciI mutant nor the double cciI cepI mutant was deficient in attachment, and restoration of the cciI gene resulted in less attachment than for the mutants. Meanwhile, the cciR mutant did show a significant reduction in attachment, as did the cciR cepIR mutant. While there was no change in antibiotic susceptibility with the individual cepIR and cciIR mutants, the cepI cciI mutant biofilms were more sensitive to ciprofloxacin. A significant increase in sensitivity to removal by sodium dodecyl sulfate was seen for the cepI and cepR mutants. Flow cell analysis of the individual cepIR mutant biofilms indicated that they were both structurally and temporally impaired in attachment and development. These results suggest that biofilm structural defects might be present in quorum-sensing mutants of B. cenocepacia that affect the stability and resistance of the adherent cell mass, providing a basis for future studies to design preventative measures against biofilm formation in this species, an important lung pathogen of cystic fibrosis patients. 相似文献
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Eva?FreyhultEmail author Peteris?Prusis Maris?Lapinsh Jarl?ES?Wikberg Vincent?Moulton Mats?G?GustafssonEmail author 《BMC bioinformatics》2005,6(1):50