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41.
Mahmud T Bode HB Silakowski B Kroppenstedt RM Xu M Nordhoff S Höfle G Müller R 《The Journal of biological chemistry》2002,277(36):32768-32774
Short chain carboxylic acids are well known as the precursors of fatty acid and polyketide biosynthesis. Iso-fatty acids, which are important for the control of membrane fluidity, are formed from branched chain starter units (isovaleryl-CoA and isobutyryl-CoA), which in turn are derived from the degradation of leucine and valine, respectively. Branched chain carboxylic acids are also employed as starter molecules for the biosynthesis of secondary metabolites, e.g. the therapeutically important anthelmintic agent avermectin or the electron transport inhibitor myxothiazol. During our studies on myxothiazol biosynthesis in the myxobacterium, Stigmatella aurantiaca, we detected a novel biosynthetic route to isovaleric acid. After cloning and inactivation of the branched chain keto acid dehydrogenase complex, which is responsible for the degradation of branched chain amino acids, the strain is still able to produce iso-fatty acids and myxothiazol. Incorporation studies employing deuterated leucine show that it can only serve as precursor in the wild type strain but not in the esg mutant. Feeding experiments using (13)C-labeled precursors show that isovalerate is efficiently made from acetate, giving rise to a labeling pattern in myxothiazol that provides evidence for a novel branch of the mevalonate pathway involving the intermediate 3,3-dimethylacryloyl-CoA. 3,3-Dimethylacrylic acid was synthesized in deuterated form and fed to the esg mutant, resulting in strong incorporation into myxothiazol and iso-fatty acids. Similar experiments employing Myxococcus xanthus revealed that the discovered biosynthetic route described is present in other myxobacteria as well. 相似文献
42.
Kumar T Liestøl K Maehlen J Hiorth A Jettestuen E Lind H Brorson SH 《Human biology; an international record of research》2002,74(1):137-142
This study examines the distribution of apolipoprotein E (APOE) alleles in a population of healthy male and female Norwegians (n = 798) below the age of 40. The -491A/T polymorphism of the promoter region of the APOE gene was also examined. A seminested polymerase chain reaction was applied in the genotyping. The results showed that the E3 allele had the highest frequency (0.744), followed by E4 (0.198) and E2 (0.058). The APOE frequencies found in this study differ significantly from those obtained in earlier Norwegian APOE phenotypings. The allele frequencies in the -491 site of the promoter region were 0.845 for the A allele and 0.155 for the T allele. The genotype frequency was highest for AA (0.707), followed by AT (0.277) and TT (0.016). Moreover, the A allele was in linkage disequilibrium to E4. 相似文献
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Syntenic relationships between Medicago truncatula and Arabidopsis reveal extensive divergence of genome organization 总被引:4,自引:0,他引:4 下载免费PDF全文
Zhu H Kim DJ Baek JM Choi HK Ellis LC Küester H McCombie WR Peng HM Cook DR 《Plant physiology》2003,131(3):1018-1026
Arabidopsis and Medicago truncatula represent sister clades within the dicot subclass Rosidae. We used genetic map-based and bacterial artificial chromosome sequence-based approaches to estimate the level of synteny between the genomes of these model plant species. Mapping of 82 tentative orthologous gene pairs reveals a lack of extended macrosynteny between the two genomes, although marker collinearity is frequently observed over small genetic intervals. Divergence estimates based on non-synonymous nucleotide substitutions suggest that a majority of the genes under analysis have experienced duplication in Arabidopsis subsequent to divergence of the two genomes, potentially confounding synteny analysis. Moreover, in cases of localized synteny, genetically linked loci in M. truncatula often share multiple points of synteny with Arabidopsis; this latter observation is consistent with the large number of segmental duplications that compose the Arabidopsis genome. More detailed analysis, based on complete sequencing and annotation of three M. truncatula bacterial artificial chromosome contigs suggests that the two genomes are related by networks of microsynteny that are often highly degenerate. In some cases, the erosion of microsynteny could be ascribed to the selective gene loss from duplicated loci, whereas in other cases, it is due to the absence of close homologs of M. truncatula genes in Arabidopsis. 相似文献
46.
Formation and nuclear export of tRNA, rRNA and mRNA is regulated by the ubiquitin ligase Rsp5p 总被引:3,自引:0,他引:3
Neumann S Petfalski E Brügger B Grosshans H Wieland F Tollervey D Hurt E 《EMBO reports》2003,4(12):1156-1162
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Transgenic tobacco (Nicotiana tabacum L.) plants with decreased and increased transport capacities of the chloroplast triose phosphate/phosphate translocator (TPT)
were used to study the control the TPT exerts on the flux of starch and sucrose biosynthesis, as well as CO2 assimilation, respiration and photosynthetic electron transport. For this purpose, tobacco lines with an antisense repression
of the endogenous TPT (αTPT) and tobacco lines overexpressing a TPT gene from Flaveria trinervia (FtTPT) were used. In ambient CO2, there was no or little effect of altered TPT transport activities on either rates of photosynthetic electron transport and/or
CO2 assimilation. However, in elevated CO2 (1500 μl · l−1) and low O2 (2%) the TPT exerted strong control on the rate of CO2 assimilation (control coefficient for the wild type; CJA
TPT=0.30) in saturating light. Similarly, the incorporation of 14C into starch in high CO2 was increased in tobacco plants with decreased TPT activity, but was reduced in plants overexpressing the TPT from F. trinervia. Thus, the TPT exerted negative control on the rate of starch biosynthesis with a CJStarch
TPT=−0.19 in the wild type estimated from a hyperbolic curve fitted to the data points. This was less than the positive control
strength on the rate of sucrose biosynthesis (CJSuc
TPT=0.35 in the wild type). Theoretically, the positive control exerted on sucrose biosynthesis should be numerically identical
to the negative control on starch biosynthesis unless additional metabolic pathways are affected. The rate of dark respiration
showed some correlation with the TPT activity in that it increased in FtTPT overexpressors, but decreased in αTPT plants with
an apparent control coefficient of CJRes
TPT=0.24. If the control on sucrose biosynthesis is referred to as “gain of carbon” (positive control) and the control on starch
biosynthesis as well as dark respiration as a “loss of carbon” (negative control) for sucrose biosynthesis and subsequent
export, the sum of the control coefficients on dark respiration and starch biosynthesis would be numerically similar to the
control coefficient on the rate of sucrose biosynthesis. There was also some control on the rate of photosynthetic electron
transport, but only at high light and in elevated CO2 combined with low O2. The control coefficient for the rate of photosynthetic electron transport was CJETR
TPT=0.16 in the wild type. Control coefficients were also calculated for plants with elevated and lowered TPT activity. Furthermore,
the extent to which starch degradation/glucose utilisation compensates for the lack of triose phosphate export was assessed.
The TPT also exerted control on metabolite contents in air.
Received: 26 March 1999 / Accepted: 21 August 1999 相似文献
49.
We measured the light response curve of photosynthetic oxygen evolution by illuminating a leaf disc in an air-tight windowed chamber. Oxygen production was measured by monitoring the quenching of luminescence of an organometallic ruthenium compound. A photodiode based chlorophyll a fluorometer was used to measure the luminescence intensity. Oxygen evolution measurements with a traditional oxygen electrode gave the same numerical values at different light intensities when the same leaf disk was tested. The quality of the measurement signal of the new method was found to be similar to that obtained with the oxygen electrode method. The new luminescence based system is more stable against electrical disturbances than an oxygen electrode, its response to oxygen pressure changes is very rapid, and the new method allows the same basic equipment to be used for chlorophyll fluorescence and oxygen measurements. 相似文献
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