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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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The effect of neurotensin on submaximally-stimulated hepatobiliary and pancreatic secretion was studied in 6 healthy subjects. An intravenous infusion of neurotensin 1.4 ± 0.3 pmol/kg/min, designed to reproduce plasma neurotensin immunoreactivity levels within the physiological range, produced a significant increase in pancreatic bicarbonate output. Plasma concentrations of pancreatic polypeptide rose by 83 ± 16 pmol/l and were associated with a small reduction in trypsin, but no significant change in bilirubin outputs. 相似文献
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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
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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)