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1.
Ruth C. Paul B. Rainey Brian J. Sheehan Orla M. Keane Charles J. Dorman 《Current biology : CB》1999,9(24)
The relationship between environment and mutation is complex [1]. Claims of Lamarkian mutation [2] have proved unfounded [3], [4] and [5]; it is apparent, however, that the external environment can influence the generation of heritable variation, through either direct effects on DNA sequence [6] or DNA maintenance and copying mechanisms [7], [8], [9] and [10], or as a consequence of evolutionary processes [11], [12], [13], [14], [15] and [16]. The spectrum of mutational events subject to environmental influence is unknown [6] and precisely how environmental signals modulate mutation is unclear. Evidence from bacteria suggests that a transient recombination-dependent hypermutational state can be induced by starvation [5]. It is also apparent that chnages in the mutability of specific loci can be influenced by alterations in DNA topology [10] and [17]. Here we describe a remarkable instance of adaptive evolution in Salmonella which is caused by a mutation that occurs in intermediate-strength osmotic environments. We show that the mutation is not ‘directed’ and describe its genetic basis. We also present compelling evidence in support of the hypothesis that the mutational event is constrained by signals transmitted from the external environment via changes in the activity of DNA gyrase. 相似文献
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A two-step (indirect) immunoperoxidase method directed against Chlamydia trachomatis was developed. The method was then used to evaluate the specificity of cytologic changes suggestive of C. trachomatis in Papanicolaou smears of cervical specimens from women who were culture-negative for the organism. Positive immunoperoxidase staining was detected in 9 of 21 cases (43%) tested. Technical problems, especially background staining, precluded interpretation in the remainder of the cases. Cervical cytology, as demonstrated by immunoperoxidase staining, may, in some instances, be more sensitive than the culture. However, because the etiology of cytologic changes not specifically identified by immunoperoxidase staining may be due to other organisms or factors, immunoperoxidase procedures, as described, should not replace culture for confirmation of cytologic findings suggestive of C. trachomatis. 相似文献
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6.
P M Shaffer J R Cairns D C Dorman A M Lott 《The International journal of biochemistry》1984,16(4):429-434
Partially purified preparations from Aspergillus nidulans were shown to catalyze two alpha-ketoglutarate dependent dioxygenase reactions: the pyrimidine deoxyribonucleoside 2'-hydroxylase (EC 1.14.11.3) and the thymine 7-hydroxylase (EC 1.14.11.6) reactions. These reactions showed an absolute requirement for alpha-ketoglutarate and molecular oxygen and were stimulated by Fe(II), ascorbate and catalase. Both reactions demonstrated a stoichiometry such that for each mole of substrate (deoxyribonucleoside or pyrimidine) hydroxylated one mole of CO2 was produced from alpha-ketoglutarate. These two activities were separated using DEAE-Sephacel chromatography. 相似文献
7.
CJ von Ruhland 《Biotechnic & histochemistry》2013,88(7):478-484
Amplification of immunohistochemical markers received considerable attention during the 1980s and 1990s. The amplification approach was largely abandoned following the development of antigen retrieval and reporter amplification techniques, because the latter were incorporated more easily into high throughput automated procedures in industrial and diagnostic laboratories. There remain, however, a number of instances where marker amplification still has much to offer. Consequently, we examined experimentally the utility of an optimized marker amplification technique in diagnostically relevant tissue where either the original signal strength was low or positive sites were visible, but sparsely distributed. Marker amplification in the former case not only improved the visibility of existing positive sites, but also revealed additional sites that previously were undetectable. In the latter case, positive sites were rendered more intense and therefore more easily seen during low magnification examination of large areas of tissue. 相似文献
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Anna H. van’t Hoog Frank Cobelens Anna Vassall Sanne van Kampen Susan E. Dorman David Alland Jerrold Ellner 《PloS one》2013,8(12)
Background
High costs are a limitation to scaling up the Xpert MTB/RIF assay (Xpert) for the diagnosis of tuberculosis in resource-constrained settings. A triaging strategy in which a sensitive but not necessarily highly specific rapid test is used to select patients for Xpert may result in a more affordable diagnostic algorithm. To inform the selection and development of particular diagnostics as a triage test we explored combinations of sensitivity, specificity and cost at which a hypothetical triage test will improve affordability of the Xpert assay.Methods
In a decision analytical model parameterized for Uganda, India and South Africa, we compared a diagnostic algorithm in which a cohort of patients with presumptive TB received Xpert to a triage algorithm whereby only those with a positive triage test were tested by Xpert.Findings
A triage test with sensitivity equal to Xpert, 75% specificity, and costs of US$5 per patient tested reduced total diagnostic costs by 42% in the Uganda setting, and by 34% and 39% respectively in the India and South Africa settings. When exploring triage algorithms with lower sensitivity, the use of an example triage test with 95% sensitivity relative to Xpert, 75% specificity and test costs $5 resulted in similar cost reduction, and was cost-effective by the WHO willingness-to-pay threshold compared to Xpert for all in Uganda, but not in India and South Africa. The gain in affordability of the examined triage algorithms increased with decreasing prevalence of tuberculosis among the cohort.Conclusions
A triage test strategy could potentially improve the affordability of Xpert for TB diagnosis, particularly in low-income countries and with enhanced case-finding. Tests and markers with lower accuracy than desired of a diagnostic test may fall within the ranges of sensitivity, specificity and cost required for triage tests and be developed as such. 相似文献10.
The experiment was organized in a 3×2 factorial arrangement with three dietary fat blends and a basal (20 mg kg?1 diet) or supplemented (220 mg kg?1) level of α-tocopheryl acetate. Dietary vitamin E and monounsaturated to polyunsaturated fatty acid ratio (dietary MUFA/PUFA) affected muscle α-tocopherol concentration (α-tocopherol [log μg g?1]=0.18 (±0.105)+0.0034 (±0.0003)·dietary α-tocopherol [mg kg?1 diet] (P<0.0001)+0.39 (±0.122)·dietary MUFA/PUFA (P<0.0036)). An interaction between dietary α-tocopherol and dietary MUFA/PUFA exists for microsome α-tocopherol concentration (α-tocopherol [log μg g?1]=1.14 (±0.169) (P<0.0001)+0.0056 (±0.00099)·dietary α-tocopherol [mg kg?1 diet] (P<0.0001)+0.54 (±0.206)·dietary MUFA/PUFA (P<0.0131)?0.0033 (±0.0011)·dietary α-tocopherol [mg kg?1)]×dietary MUFA/PUFA (P<0.0067)), and hexanal concentration in meat (hexanal [ng·g?1]=14807.9 (±1489.8)?28.8 (±10.6) dietary α-tocopherol [mg·kg?1] (P<0.01)?8436.6 (±1701.6)·dietary MUFA/PUFA (P<0.001)+24.0 (±11.22)·dietary α-tocopherol·dietary MUFA/PUFA (P<0.0416)). It is concluded that partial substitution of dietary PUFA with MUFA lead to an increase in the concentration of α-tocopherol in muscle and microsome extracts. An interaction between dietary α-tocopherol and fatty acids exists, in which at low level of dietary vitamin E inclusion, a low MUFA/PUFA ratio leads to a reduction in the concentration of α-tocopherol in microsome extracts and a concentration of hexanal in meat above the expected values. 相似文献