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131.
Complete inhibition of growth of sensitive L5178Y mouse lymphoma cells in culture was obtained with 10(-3)M ouabain, 1.65 X 10(-3)M thymidine, 1.8 X 10(-4)M thioguanine and 10(-6)M cytosine arabinoside. The toxicity of methotrexate was dependent upon cell density and this compound was excluded from further study. The expression time before addition of the selective agent was important for detecting EMS induced resistant variants. Ouabain-resistant variants appeared immediately after treatment and were present over a broad time span. No excess thymidine- or thioguanine-resistant variants were seen initially; a peak in variant numbers was seen for excess thymidine resistance at 48-96 h and for thioguanine resistance at 144-192 h. Using induced mutation frequencies at optimum expression times, equal EMS treatments yielded substantially more variants resistant to thioguanine than to ouabain. It is suggested that this difference may have origin in possible constraints in the classes of mutants which are permissible in a vital function, maintenance of the Na+/K+ balance, when compared with a non-vital function, salvage purine biosynthesis. Some data are presented on the stability in culture of resistant variants. A limited number of observations were made following treatment in the peritoneal cavity of the mouse which were in broad agreement with the above results. 相似文献
132.
Piotr Cysewski 《Journal of molecular modeling》2009,15(6):597-606
The energies of intra- and inter-strand stacking interactions in model d(GpC) and d(CpG) two-base-pair steps were estimated
by MP2/aug-cc-pVDZ single point calculations corrected for basis superposition errors. The stacked two-nucleobase pairs were
constructed using experimental values of base pair and base step parameters taken from Nucleic Acid Database (). Three distinct polymorphic forms were analysed, namely A-, B- and Z-DNA. The applied methodology enables statistical analysis
of structural and energetic diversities. The structural relationships between polymorphic forms are quite complex and depend
on the sequence of pairs. The variability of parameters such as shift and tilt is almost the same irrespective of the polymorphic form and sequence of steps analysed. In contrast, shift and twist distributions easily discriminate all three polymorphic forms of DNA. Interestingly, despite significant structural diversities,
the energies of the most frequent energy ranges are comparable irrespective of the polymorphic form and base sequence. There
was observed compensation of inter- and intra-strand interactions, especially for d(GpC) and d(CpG) steps found in A- and
B-DNA. Thus, among many other roles, these pairs act as a kind of energetic buffer, balancing the double helix.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
133.
Complex splicing patterns of RNAs from the early regions of adenovirus-2 总被引:172,自引:0,他引:172
134.
Thomas P. West Mark S. Shanley Gerard A. ODonovan 《Biochimica et Biophysica Acta (BBA)/General Subjects》1982,719(2):251-258
Cytosine deaminase (EC 3.5.4.1) from Salmonella typhimurium has been purified 419-fold to apparent homogeneity. SDS polyacrylamide gel electrophoresis indicated that the final cytosine deaminase preparation was homogenous. The molecular weight of cytosine deaminase was determined to be approx. 230 000 containing four identical subunits with each subunit having a molecular weight of 54 000. Cytosine deaminase has a pH optimum of 7.30 to 7.50 and a temperature optimum of 45 to 50°C. Cytosine was deaminated specifically; 5-fluorocytosine was deaminated to a lesser extent. The Km and V values for cytosine were 0.74 mM and 47.16 μmole/min, respectively. As effectors of enzyme activity, PPi stimulated the deamination while metal ions and orotidine monophosphate inhibited it. The physical characteristics of cytosine deaminase lend credence to its proposed salvage role in pyrimidine metabolism as indicated previously by physiological studies (West, T.P. and O'Donovan, G.A., J. Bacteriol. (1982) 149, 1171–1174). 相似文献
135.
Kazunobu Miura Shigeki Tsuda Tatsuyoshi Iwano Tohru Ueda Fumio Harada Nobuyuki Kato 《Biochimica et Biophysica Acta (BBA) - Gene Structure and Expression》1983,739(2):181-189
Cytosine residues of nucleic acids were converted to 4-thiouracil residues with hydrogen sulfide in pyridine and water to examine the secondary and tertiary structures of mouse 5 S rRNA. The cytosine residues at positions 10, 24, 34 (or 36), 39, 44 (or 46) and 63 were converted preferentially when the treatment was carried out at 28°C. This result supports the model of the secondary structure of 5 S rRNA of Nishikawa, K. and Takemura, S. ((1974) FEBS Lett. 40, 106–109) consisting of five helices and five loops. As the temperature was increased to 35°C, additional cytosine residues in positions 26, 52 and 78 were modified to moderate extents. 相似文献
136.
Jeanne M. Manson Michael L. Dourson Carl C. Smith 《In vitro cellular & developmental biology. Plant》1977,13(7):434-442
Summary When pregnant mice were exposed to 40 mg per kg of cytosine arabinoside (ara-C) on days 10 to 12 of gestation, adactylous
limbs with large, distally located blisters were found when the fetuses were examined on day 18. Embryonic limbs exposed transplacentally
under identical conditions and explanted to culture exhibited the same morphological abnormality as did limbs exposed directly
in culture to 0.1 to 1 μg per ml of ara-C. Two noncytotoxic analogues of ara-C, uridine arabinoside (ara-U) and hypoxanthine
arabinoside (ara-HX), had no influence on morphological differentiation of limbs in vitro. Ara-C alone caused a dose-related
decrease in uptake of3H-thymidine and35SO4 in cultured limb buds. Production of this morphologically distinct malformation in vitro will allow detailed biochemical
investigations on the effect of ara-C limb ectodermal-mesenchymal interactions.
Supported by NIH Postdoctoral Fellowship No. CM02660.
Supported by NIEHS Predoctoral Fellowship No. ES00127.
Supported by NIEHS Toxicology Training Grant No. ES00127. 相似文献
137.
New fluorescent polymeric materials were synthesized by grafting the nucleobase cytosine on to the backbone of agarose and κ-carrageenan, employing a rapid water based method under microwave irradiation using potassium persulphate (KPS) as an initiator. The emission spectrum of the modified agarose and κ-carrageenan recorded in aqueous solution (5 × 10−5 M) exhibited emission maxima (λem,max) at 348 nm by excitation at 266 nm. The emission intensity was enhanced by ca. 104% and 60% compared to that of pure cytosine solution of the same concentration. When the concentration of the pure cytosine solution is made equivalent to the concentration of the cytosine molar component (3.09 × 10−5) and (3.5 × 10−5) present in 5 × 10−5 M solution of modified agarose and κ-carrageenan, respectively, then ca. 143% and 81% enhancement in emission intensity was observed. The remarkable fluorescent activity of the agarose-cytosine derivative may have potential uses as sensor in various applications. 相似文献