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61.
Evolution of transposable elements: an IS10 insertion increases fitness in Escherichia coli 总被引:3,自引:0,他引:3
Strains of Escherichia coli carrying Tn10, a transposon consisting of two
IS10 insertion sequences flanking a segment encoding for a
tetracycline-resistance determinant, gain a competitive advantage in
chemostat cultures. All Tn10-bearing strains that increase in frequency
during competition have a new IS10 insertion that is found in the same
location in the genome of those strains. We mapped, by a gradient of
transmission, the position of the new IS10 insertion. We examined 11
isolates whose IS10 insertion was deleted by recombinational crossing-
over, and in all cases the competitive fitness of the isolates was
decreased. These results show that the IS10-generated insertion increases
fitness in chemostat cultures. We named the insertion fit::IS10 and suggest
that transposable elements may speed the rate of evolution by promoting
nonhomologous recombination between preexisting variations within a genome
and thereby generating adaptive variation.
相似文献
62.
Members of the ZFY and ZNF6 gene families have been cloned from species
representing different taxa and different modes of sex determination.
Comparisons of these genes show the ZFY-like and ZNF6 sequences to be
strongly conserved across marsupials, birds, and lepidosaurians. Sequence
analyzed by neighbor-joining indicated that both gene families are
monophyletic with a high bootstrap value. Pairing of sequences from males
and females of nonmammalian species showed there to be no significant
difference between male and female sequences from a single species,
consistent with autosomal locations. The molecular distances between murine
Zfy-1, Zfy-2, and other ZFY-like sequences suggested that Zfy genes have
undergone a period of rapid evolutionary change not seen in human ZFY.
相似文献
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Kinetic studies of the reverse reaction catalysed by adenosine triphosphate–creatine phosphotransferase. The inhibition by magnesium ions and adenosine diphosphate 下载免费PDF全文
1. Kinetic investigations of the reaction catalysed by ATP–creatine phosphotransferase have been carried out. 2. No firm conclusions could be reached about the reaction of Mg2+ at the nucleotide-binding site of the enzyme. The value of the kinetic constant for this reaction depends on the value used for the apparent stability constant of the metal ion–nucleotide complex and, to a smaller extent, on the method of plotting the results. 3. At higher concentrations Mg2+ is a non-competitive inhibitor of the enzyme with respect to both MgADP− and phosphocreatine. 4. ADP3− is a competitive inhibitor of the enzyme with respect to MgADP− and a non-competitive inhibitor with respect to phosphocreatine. 5. The concentration of phosphocreatine has little, if any, effect on the kinetic constants for the nucleotide reactants. 相似文献
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Retroviral Splicing Suppressor Requires Three Nonconsensus Uridines in a 5′ Splice Site-Like Sequence 下载免费PDF全文
Robert E. Paca Catherine S. Hibbert Christopher T. O''Sullivan Karen L. Beemon 《Journal of virology》2001,75(16):7763-7768
Rous sarcoma virus RNA contains a negative regulator of splicing (NRS) element that aids in maintenance of unspliced RNA. The NRS binds U1 snRNA at a sequence that deviates from the 5' splice site consensus by substitution of U's for A's at three positions: -2, +3, and +4. All three of these U's are important for NRS-mediated splicing suppression. Substitution of a single nonconsensus C or G at any of these sites diminished NRS activity, whereas substitution of a single A generated a preferred 5' splice site within the NRS. 相似文献
68.
The conversion of cephalosporins to 7 alpha-methoxycephalosporins by cell-free extracts of Streptomyces clavuligerus. 总被引:3,自引:1,他引:2 下载免费PDF全文
In the presence of S-adenosylmethionine, 2-oxoglutarate, Fe2+ and a reducing agent, cell-free extracts of Streptomyces clavuligerus convert cephalosporin C and O-carbamoyldeacetylcephalosporin C into 7 alpha-methoxy derivatives. No synthesis of a 7 alpha-methoxy derivative of deacetylcephalosporin C was detected in the system used, and the 7 alpha-methoxy derivative of deacetoxycephalosporin C was produced only in relatively small amounts. It appears that the 7 alpha-methoxy group is introduced after the cephalosporin ring system has been formed and that its introduction may represent the final step in a biosynthetic pathway. 相似文献
69.
Afiya Jahan Tanjia Taher Nipa SM Majharul Islam Md. Helal Uddin Md. Sadiqul Islam Md. Shahjahan 《Zeitschrift fur angewandte Ichthyologie》2019,35(4):994-1003
Salinity intrusion in the coastal freshwater rivers due to climate change and construction of the dam in the upstream rivers are alarming in aquaculture. Hence, an experiment was conducted to know the effects of salinity on growth performance, hemato‐biochemical parameters and erythrocytes structure in a commercially cultivable catfish species, striped catfish (Pangasianodon hypophthalmus). Firstly, median lethal concentration (LC50) of salinity for striped catfish was determined and then the fish were exposed to three salinity conditions (4, 8 and 12‰) and a control (0‰). Fish were sacrificed at day 7, 14, 28 and 56 after the start of salinity exposure. The 96 hr LC50 value was found to be 14.87‰. Salinity levels from freshwater to 8‰ showed optimal conditions with high survival rate and good growth performances of fish in terms of weight gain and specific growth rate (SGR). Interestingly, the lowest food conversion ratio (FCR) was found in 4‰ group. The hemoglobin (Hb) level and number of red blood cells (RBCs) were found to be decreased significantly in 8 and 12‰ compared to 0 and 4‰ at the initial days of exposure, while number of white blood cells (WBCs) and glucose level showed opposite scenario. Frequencies of ENA (erythrocytic nuclear abnormalities) and ECA (erythrocytic cellular abnormalities) were significantly increased with increasing salinities in the initial days of exposure. Overall, findings of the present study revealed that striped catfish might be suitable fish species for culture in the brackish water containing salinity up to 10‰. 相似文献
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