Radiation sensitization by thiol-binding agents of radio-resistant and radiosensitive Escherichia coli and the oxygen effect

Dose-survival curves of four strains of E. coli-B/r her- try-, Bs-1, B/r CSH, and 15T-were obtained in the presence and in the absence of non-toxic levels of several thiol-binding agents-N-ethylmaleimide (NEM), iodoacetamide (IA), and hydroxymercuribenzoate (HMB). The degree of radiosensitization by these agents was estimated from the increase in slope of the dose-survival curve, under anoxic and aerobic conditions. Chemical sensitization of both radioresistant and radiosensitive strains of bacteria with the thiol-binding enzyme poisons NEM, IA, and HMB has been observed. NEM sensitized only under anoxic conditions, IA sensitized under both anoxic and aerobic conditions, although to a much greater extent aerobically, and HMB sensitized only under aerobic conditions. The formation of long-lived radiolytic products toxic to bacteria is observed in sensitization by IA. When sensitization occurs, the magnitude of the dose-modifying factor is equal to or greater than the oxygen enhancement ratio. Inhibition of an energy-requiring enzymic repair process does not seem to be involved as a primary mechanism of sensitization. Interference by thiol-binding agents with a "rapid repair" process which is different from the usual "enzymic repair," and which operates in radio-sensitive as well as in radioresistant bacteria, is suggested.     

SARCOCYSTIS MURIS BLANCHARD BEI EINER MICROTUSART

Aus dem umfangreichen Material der oben angef(?)hrten Sammelreise erhielt ich von Herrn Dr. R. Piechocki eine in einer Schlagfalle gefangene, bereits entpelzte Microtusart. Die Bestimmung ergab Microtus maximowiczii Schrenk. Pr(?)ft man die Literatur (?)ber Sarcosporidienbefall nach, so findet man bis     

Virustat, a device for continuous production of viruses

Methods for continuous production of viruses, and operation of the virustat, an apparatus in which such production was accomplished, were studied. Continuous production requires a separate continuous host growth chamber, such as the chemostat, and a multiunit virus growth chamber into which the virus-inoculated host cells are led. Successful continuous output of MS-2 and ϕX174 viruses, the latter in lysates, over periods of several days and at titers approximating those of batch lysates, was observed. Design problems include chamber sizes and flow rates, growth of resistant mutants within both virus and host growth chambers, clogging by lysis debris, and the phenomenon of self-inoculation. The latter represents virus growth in the first section of the chamber in excess of the washout rate, leading to lack of need for virus inoculation after an initial period. Use of the virustat for production and research purposes will require some attention to the formation of resistant bacterial colonies at pockets and surface sites of limited washout. With the virustat as a continuous virus production device, continuous purification methods are desirable. Research use of the virustat in continuous mutagenic population studies would require suppression of self-inoculation by use of many sections in the chamber, and improved servo control of host populations at low concentrations.     

Analysis of Cytokinin Metabolism in ipt Transgenic Tobacco by Liquid Chromatography-Tandem Mass Spectrometry

The endogenous levels of the major, naturally occurring cytokinins in Pisum sativum ribulose-1,5-bisphosphate carboxylase small subunit promoter-isopentenyl transferase gene (Pssu-ipt)-transformed tobacco (Nicotiana tabacum L.) callus were quantified using electrospray-liquid chromatography-tandem mass spectrometry during a 6-week subcultivation period. An ipt gene was expressed under control of a tetracycline-inducible promoter for a more detailed study of cytokinin accumulation and metabolism. Activation of the ipt in both expression systems resulted in the production of mainly zeatin-type cytokinins. No accumulation of isopentenyladenine or isopentenyladenosine was observed. In Pssu-ipt-transformed calli, as well as in the tetracycline-inducible ipt leaves, metabolic inactivation occurred through O-glucoside conjugation. No significant elevation of cytokinin N-glucosides levels was observed. Side-chain reduction to dihydrozeatin-type cytokinins was observed in both systems. The levels of the endogenous cytokinins varied in time and were subject to homeostatic regulatory mechanisms. Feeding experiments of ipt transgenic callus with [3H]isopentenyladenine and [3H]isopentenyladenosine mainly led to labeled adenine-like compounds, which are degradation products from cytokininoxidase activity. Incorporation of radioactivity in zeatin riboside was observed, although to a much lesser extent.     

人粒细胞集落刺激因子（hG－CSF）cDNA3′－UTR对其表达的影响

利用人粒细胞集落刺激因子（ｈＧ－ＣＳＦ）ｃＤＮＡ３′端非翻译区（３′－ＵＴＲ）中存在的ＤｒａⅠ酶切位点,通过部分酶切与完全酶切,删除３′－ＵＴＲ不同长度,构建了四种ｈＧ－ＣＳＦｃＤＮＡ瞬时重组表达质粒。转染ＣＯＳ－７细胞后,生物活性测定结果提示,ｈＧ－ＣＳＦｃＤＮＡ３′－ＵＴＲ对其表达起负调控作用,其关键性序列位于紧接终止密码子ＴＧＡ下游的６５ｂｐ范围内,３′－ＵＴＲ对ｈＧ－ＣＳＦｃＤＮＡ表达的影响与转录水平的差别有一定关系。