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排序方式: 共有492条查询结果,搜索用时 15 毫秒
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A two-component signal-transducing system is involved in competence and penicillin susceptibility in laboratory mutants of Streptococcus pneumoniae 总被引:14,自引:6,他引:8
Eric Guenzi Anne-Marie Gasc Michel A. Sicard Regine Hakenbeck 《Molecular microbiology》1994,12(3):505-515
Penicillin resistance in Streptococcus pneumoniae has been attributed so far to the production of penicillin-binding protein (PBP) variants with decreased affinities for β-lactam antibiotics. Cefotaxime-resistant laboratory mutants, selected after several steps on increasing concentrations of this β-lactam, become deficient in transformation as well. A DNA fragment conferring both cefotaxime resistance and transformation deficiency was isolated and cloned from the mutant C306. The cefotaxime resistance associated with this resistance determinant was not accompanied with apparent changes in PBP properties, and it mapped on the chromosome distinct from the known resistance determinants, genes encoding PBP2x, PBP1a or PBP2b. Determination of a 2265 bp DNA sequence of the resistance determinant revealed two open reading frames, claR and claH, whose deduced amino acid sequence identified the corresponding proteins as the response regulator and histidine kinase receptor, respectively (members of the two families of bacterial signal-transducing proteins). Two hydrophobic peptide regions divided the histidine kinase ClaH into two putative domains: an N-terminal extracelluiar sensor part, and an intracelluiar C-terminal domain with the conserved His-226 residue, the presumed phosphorylation site. The single point mutations responsible for cefotaxime-resistance and transformation deficiency of C306 and of another two independently isolated cefotaxime-resistant mutants were each located in the C-terminal half of ClaH. A small extracellular protein, the competence factor, is required for induction of competence. Neither C306 nor the transformants obtained with the mutated claH gene produced competence factor, and exogenous competence factor could not complement the transformation deficiency, indicating that the signal-transducing system cia is involved in early steps of competence regulation. 相似文献
3.
Gundula Thiel Tanka Lozanova Siegfried Vogel Dieter Kintzel Werner Jänisch Regine Witkowski 《Human genetics》1993,91(6):547-550
We report a cytogenetic investigation of 55 low-grade astrocytomas in 52 patients, 15 children and 37 adults. In addition to numerical aberrations such as trisomy 7 and gonosomal losses, we found structural and/or numerical aberrations of chromosome 1 in eight astrocytomas. There was a striking difference between the rearranged chromosomes in pediatric and adult patients. Whereas the pediatric tumors revealed monosomies 1p with accompanying trisomy 1q, the astrocytomas in adults showed partial or complete monosomies 1q. 相似文献
4.
Regine Hengge-Aronis 《Molecular microbiology》1996,21(5):887-893
It is now well established that the σS subunit of RNA polymerase is a master regulator in a complex regulatory network that governs the expression of many stationary-phase-inducible genes in Escherichiacoli. In this review, more recent findings will be summarized that demonstrate that σS also acts as a global regulator for the osmotic control of gene expression, and actually does so in exponentially growing cells. Thus, many σS-dependent genes are induced during entry into stationary phase as well as in response to osmotic upshift. K+ glutamate, which accumulates in hyperosmotically stressed cells, seems to specifically stimulate the activity of σS-containing RNA polymerase at σS-dependent promoters. Moreover, osmotic upshift results in an elevated cellular σS level similar to that observed in stationary-phase cells. This increase is the result of a stimulation of rpoS translation as well as an inhibition of the turnover of σS, which in exponentially growing non-stressed cells is a highly unstable protein. Whereas the RNA-binding protein HF-I, previously known as a host factor for the replication of phage Qβ RNA, is essential for rpoS translation, the recently discovered response regulator RssB, and ClpXP protease, have been shown to be required for σS degradation. The finding that the histone-like protein H-NS is also involved in the control of rpoS translation and σS turnover, sheds new light on the function of this protein in osmoregulation. Finally, preliminary evidence suggests that additional stresses, such as heat shock and acid shock, also result in increased cellular σS levels in exponentially growing cells. Taken together, σS function is clearly not confined to stationary phase. Rather, σS may be regarded as a sigma factor associated with general stress conditions. 相似文献
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Peter Miethe Ingeborg Jansen Uwe Niedermeyer Udo Kragl Regine Haftendorn Maria-Regina Kula Christian Wandrey Karl-Heinz Mohr Helmut-Walter Meyer 《Biocatalysis and Biotransformation》1992,7(1):61-73
The possibility of using the enzyme (R)-Oxynitrilase in a biphasic lyotropic liquid crystal/dibutylether system has been demonstrated. This reaction system is applicable for the continuous production of (R)-benzaldehydecyanohydrin in a fixed bed reactor. The optical purity was between 94 and 96% ee and independent of the flow rate. The space time yield was maximal (2650 g/(1*d)) at a flow rate of 1.6 ml/min. 相似文献
7.
Dipl. Geol. Ina Potthast 《Facies》1992,27(1):105-111
Summary The growth history of some recentPorites colonies of Mauritius Island (Indian Ocean) was dated by sclerochronological methods. Couples of high-density and low-density
bands represent the annual growth rate of the corals and allow the growth pattern of every year in the corallum to be counted.
The growth and structure of the skeletons ofPorites solida andPorites lutea were investigated. Older parts of the aragonitic skeleton in these 10 to 20 year old corals show various secondary microstructures
resulting from alterations and thickenings of the elements of the skeleton.
The primary needle-like aragonite crystals are absent in older parts of the corallum and blocky aragonitic cements can occur.
Pores and primary skeletal elements are overgrown by new microstructures. These microstructures are caused by secondary cementation
and exhibit frontal zones (Stirnzonen), zigzag-like and pseudolamellar-structures. The lamellar structures can be compared
with similar structures in the exoskeleton of some Rugosa.
A very short early diagenesis within the recent corals is responsible for the thickening and alteration of skeletal elements.
It occurs only 4 to 5 years after the formation of the skeleton and tends to increase in importance in older parts of the
corallum. Nevertheless, there is no proof for any alteration of aragonite to calcite. 相似文献
8.
Dietrich Werner Arno Krotzky Regine Berggold Heidemarie Thierfelder Marianne Preiß 《Archives of microbiology》1982,132(1):51-56
Specific nitrogenase activity inAzospirillum brasilense ATCC 29145 in surface cultures under air is enhanced from about 50 nmol C2H4·mg protein-1·h-1 to 400 nmol C2H4 by the addition of 1 mM phenol. 0.5 and 2 mM phenol added increase the rate 5-fold and 4-fold. This enhancement effect is observed only between 2 and 3 days after inoculation, with only a small reduction of the growth of the cells by the phenol added. In surface cultures under 1% O2, nitrogenase activity is slightly reduced by the addition of 1–0.01 mM phenol. Utilization of succinate is enhanced during the period of maximum enhancement of nitrogenase activity by 60% by addition of 1 mM phenol. The cells did not produce14CO2 from [U-14C] phenol, neither in surface cultures nor in liquid cultures and less than 0.1% of the phenol was incorporated into the cells. A smaller but significant enhancement of nitrogenase activity by about 100% in surface cultures under air was found withKlebsiella pneumoniae K 11 after addition of 1 mM phenol. However, inRhizobium japonicum 61-A-101 all phenol concentrations above 0.01 mM reduced nitrogenase activity. With 1 mM phenol added activity was reduced to less than 10% with no effect on the growth in the same cultivation system. With thisRhizobium japonicum strain significant quantities of phenol (25 mol in 24 h by 2·1012 cells) were metabolized to14CO2, with phenol as sole carbon source. WithAzospirillum brasilense in liquid culture under 1% and 2% O2 in the gas phase, no enhancement of nitrogenase activity by phenol was noticed. 相似文献
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