Influence onEuglena gracilis of three types of inhibitors

Three groups of antibiotics were established according to their mechanism of action on the incorporation of¹⁴C-labelled precursors inEuglena gracilis:1. antibiotics markedly inhibiting nucleic acid synthesis and negligibly affecting protein synthesis and inducing permanently bleachedE. gracilis; 2. antibiotics markedly inhibiting protein synthesis and only moderately nucleic acid synthesis and not causing permanent bleaching ofE. gracilis; 3. compounds inhibiting both protein synthesis and nucleic acid synthesis to a similar degree, some of them bringing about permanent bleaching ofE. gracilis. Nitrofurantoin was comparable to compounds of the first group, sodium azide to those of the third group. Both exhibited 100 % bleaching ofE. gracilis, although with the latter this occurred only after a short-term increase of the incubation temperature from 25 to 37 °C.     

Effect of undernutrition on DNA and RNA synthesis in subcellular fractions from different regions of the developing rat brain

The effect of undernutrition on the incorporation of [methyl-³H]thymidine into DNA and of 5-[³H]uridine into RNA of cerebral hemispheres, cerebellum, and brain stem was studied in vivo and in vitro in rats. The labeling of DNA from nuclei and mitochondria and of RNA from nuclei, mitochondria, microsomes, and soluble fractions, was also measured in vitro. The results demonstrate that nucleic acid synthesis is impaired and delayed during undernutrition. Specific effects were observed for the different brain regions and subcellular fractions: at 10 days nuclear and mitochondrial DNA and RNA synthesis was impaired, whereas at 30 days only the mitochondrial nucleic acid synthesis was affected.The delay of DNA and RNA labeling, caused by undernutrition, was most evident in the cerebellum, probably due to its intense cell proliferation during postnatal development. The specific sensitivity of mitochondria as compared to other subcellular fractions, may be due to the intense biogenesis and/or turnover of nucleic acids in brain mitochondria not only during postnatal development, but also in the adult animal.     

The labelling of nucleic acids by radioactive precursors in the blue-green algae Anacystis nidulans and Synechocystis aquatilis Sanv.

Summary The labelling of nucleic acids of growing cells of the blue-green algae Anacystis nidulans and Synechocystis aquatilis by radioactive precursors has been studies. A. nidulans cells most actively incorporate radioactivity from [2-¹⁴C]uracil into both RNA and DNA, while S. aquatilis cells incorporate most effectively [2-¹⁴C]uracil and [2-¹⁴C]thymine.Deoxyadenosine does not affect incorporation of label from [2-¹⁴C]thymidine into DNA, but weakly inhibits [2-¹⁴C]thymine incorporation into both nucleic acids and significantly suppresses the incorporation of [2-¹⁴C]uracil.The radioactivity from [2-¹⁴C]uracil and [2-¹⁴C]thymine is found in RNA uracil and cytosine and DNA thymine and cytosine. The radioactivity of [2-¹⁴C]thymidine is incorporated into DNA thymine and cytosine. These results and data of comparative studies of nucleic acid labelling by [2-¹⁴C]thymine and [5-methyl-¹⁴C]thymine suggest that the incorporation of thymine and thymidine into nucleic acids of A. nidulans and S. aquatilis is accompanied by demethylation of these precursors. In this respect blue-green algae resemble fungi and certain green algae.     

Nucleic acids methylation of synchronized BHK 21 HS 5 fibroblasts during the mitotic phase

The methylation of nucleic acids has been investigated during the cell cycle of an asparagine dependent strain of transformed fibroblasts (BHK 21 HS 5). The synchrony was carried out by a partial asparagine starvation of cells for 24 hours. The amino acid supply induced all cells to enter synchronously the G₁ phase. Methylation and DNA synthesis were respectively measured by pulsed [methyl-¹⁴C] methionine and [methyl-³H] thymidine incorporation. DNA methylation followed a biphasic pattern with maximal methyl incorporations during both S phase and mitosis. A partial desynchronisation induced the S phase of the second cycle to proceed before all the cells have achieved their division. Hydroxyurea was used in order to inhibit the DNA synthesis of cells entering the second cell cycle, which might interfer with the mitosis of the first one. The inhibitor was added either at the first beginning of cell division or during all the G₁ phase. In both conditions it suppressed ³H thymidine incorporation of the second cycle. However, mitosis took place and methylations occurred as in previous experiments. The DNA methylation of the mitotic phase in the first cell cycle could thus be dissociated from the classical post-synthetic DNA maturation and did not correspond to any DNA methylation appearing in the course of the second cell cycle.     

BIOCHEMICAL CHANGES IN YEAST DURING SPORULATION. I. FATE OF NUCLEIC ACIDS AND RELATED COMPOUNDS

Changes in nuclear figures and in activities of nucleic acid and protein syntheses were observed mainly on Saccharomyces cerevisiae G2-2 during sporogenesis. Patterns of DNA synthesis and of meiosis show that the sporogenic process in yeast was divided into an induction phase (I-phase), a DNA-synthesizing phase (S-phase) and a maturation phase (M-phase). Meiotic figures appeared most frequently at the end of the S-phase at approximately 12 hr in sporulation culture. In M-phase visible spores formed. The amount of protein increased in the initial 7 hr culture of 1-phase, then decreased in the S- and M-phases. But in sporulation culture of the asporogenic diploid strain 3c × a, protein did not decrease. RNA increased within 3 hr of the I-phase then stopped increasing. DNA synthesis occurred critically during S-phase, i.e. between 7 and 12 hr. and was somewhat resumed during the later part of M-phase. Oligodeoxyri-bonucleotide content decreased in the I- and M-phases and increased temporarily. Deoxyribosides decreased linearly during the sporogenic processes. Based on these results and results of experiments estimating the incorporation of ¹⁴C-uracil into nucleic acid and ¹⁴C-amino acid mixture into protein fractions, the roles of nucleic acid synthesis activities in meiosis and in sporulation are discussed.     

AUTORADIOGRAPHIC STUDIES OF NUCLEIC ACIDS AND PROTEINS DURING MEIOSIS IN LILIUM LONGIFLORUM

Taylor , J. Herbert (Columbia U., New York, N. Y.) Autoradiographic studies of nucleic acids and proteins during meiosis in Lilium longiflorum. Amer. Jour. Bot. 46(7): 477–484. Illus. 1959.—A study was made of the incorporation of glycine-C¹⁴, orotic acid-C¹⁴ and cytidine-H³ into nucleic acids and proteins of sporogenous and tapetal cells of lily anthers preceding and during meiosis. Methods for differential extraction of nucleic acids from tissue sections, which had been frozen, dehydrated by alcohol-substitution, and fixed in hot alcohol, were tested by chromatographic analysis of extracts. Both acid and enzyme hydrolysis were shown to be useful for quantitative or, at least, semi-quantitative work. DNA synthesis was shown to occur only during premeiotic interphase in sporogenous cells, but at two intervals in tapetal nuclei, once when the microsporocytes are in zygotene and again during pachytene. Each time the synthetic period was followed by a normal mitosis. Accumulation of RNA in microsporocytes occurred at stages up to late leptotene. After this period, labeled RNA accumulated almost exclusively in their nuclei and at a slower rate than in earlier stages. DNA synthesis, as measured by incorporation of glycine-C¹⁴ and orotic acid-C¹⁴, gave the same results and confirm earlier results with inorganic phosphate-P³². For RNA, glycine-C¹⁴ and orotic acid-C¹⁴ gave different results. When glycine-C¹⁴ was the source of label, incorporation of C¹⁴ in RNA stopped during DNA synthesis in sporogenous cells. Glycine-C¹⁴ was not utilized to a significant extent at any time by tapetal cells for RNA synthesis, but extensively for DNA and protein synthesis. Orotic acid-C¹⁴ was incorporated into RNA of both tapetum and sporogenous cells at various periods in development apparently including the interval of DNA synthesis. Protein synthesis as measured by incorporation of glycine is relatively rapid during premeiotic interphase and leptotene. It continues during the remainder of prophase, but at a much reduced rate. In tapetal cells the rate is rapid in the nuclei during periods of DNA synthesis, but even faster in both cytoplasm and nucleus after divisions are completed and the microsporocytes are in late prophase and division stages. This period of synthesis is perhaps necessary for the postmeiotic functioning of tapetum when it appears to secrete the wall materials for the microspores.     

Effects of nucleic acid compounds on viability and cell composition of Bdellovibrio bacteriovorus during starvation

The effects of various exogenous nucleic acid compounds on the viability and cell composition of Bdellovibrio bacteriovorus starved in buffer were measured. In decreasing order of effectiveness, these compounds were found to decrease the rate of loss of viability and the loss of cell carbon, cell ribonculeic acid, and cell protein: glutamate > ribonucleoside monophosphates > ribonucleosides > deoxyribonucleoside monophosphates. Similar sparing effects were not observed with nucleic acid bases, deoxyribonucleosides, ribose, ribose-5-phosphate, deoxyribose, and deoxyribose-5-phosphate. Appreciable increases in the respiration rate over the endogenous rate did not occur when cell suspensions were incubated with individual or mixtures of nucleic acid compounds. Formation of ¹⁴CO₂ by cell suspensions incubated with carbon 14-labeled nucleic acid compounds indicated ribonucleosides and ribonucleoside monophosphates were respired and to a small extent, were incorporated into cell material of non-growing cells. The respired ¹⁴CO₂ was derived mainly from the ribose portion of these molecules. No respired ¹⁴CO₂ or incorporated carbon 14 was found with bdellovibrios incubated with other nucleic acid compounds tested, including free ribose. During growth of B. bacteriovorus on Escherichia coli in the presence of exogenous UL-¹⁴C-ribonucleoside monophosphates, 10–16% of the radioactivity was in the respired CO₂ and of the radioactivity incorporated into the bdellovibrios, only 40 to 50% resided in the cell nucleic acids. However, during growth on ¹⁴C-adenine,-uracil, or-thymidine labeled E. coli, only trace amounts of ¹⁴CO₂ were found and 90% or more of the incorporated radioactivity was in the bdellovibrio nucleic acids. It is concluded that bdellovibrio can use ribonucleoside monophosphates during growth and starvation as biosynthetic precursors for synthesis of both nucleic acids and other cell materials as well as catabolizing the ribose portion for energy purposes.Abbreviations HM buffer 5 mM N-2-hydroxyethyl-piperazine-N-2-ethanesulfonic acid (pH 7.6) containing 0.1 mM CaCl₂ and MgCl₂ - DNA deoxyribonucleic acid - RNA ribonucleic acid - Ar, Cr, Gr, Ur ribonucleosides of adenine, cytosine, guanine, uracil, respectively - dTr deoxythymidine - AMP, CMP, GMP, UMP ribonucleoside monophosphates of adenine, cytosine, guanine, and uracil, respectively - dTMP deoxythymidine monophosphate - ATP adenosine triphosphate - PFU plaque-forming units     

In vitro-Verfahren zur Bestimmung der DNS-Synthese-Dauer einzelner Zellen Biochemische Voraussetzungen und Ergebnisse

Zusammenfassung Nach Hemmung der de novo-Synthese von TMP durch 5-F-UdR läuft die DNS-Synthese in vitro in Anwesenheit von 10^–5 M/l mit unveränderter Geschwindigkeit ab. Dadurch ist die DNS-Synthese-Dauer über die quantitative autoradiographische Messung des ¹⁴C-TdR-Einbaus bestimmbar. Diese in vitro-Methode wird an Rattenknochenmark und Zellen einer CML geprüft. Erste Ergebnisse zeigen eine gute Übereinstimmung mit in vivo-Messungen durch andere Methoden.

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In vitro determination of the duration of DNA synthesis of individual cells

Summary Suspended haemopoietic cells are incubated in the presence of 5-fluoro-deoxyuridine (5-F-UdR) as an inhibitor of the de novo synthesis of thymidine monophosphate (TMP). The DNA synthesis rate remains undisturbed, if 10^–5 M/l thymidine (TdR) is added. Thus, the DNA synthesis rate of individual cells can be determined by means of a quantitative autoradiographic method in measuring the incorporation rate of ¹⁴C-TdR into the DNA of the cells. DNA synthesis rates are then converted into DNA synthesis times. This in vitro method has been checked in cells of rat bone marrow and of peripheral blood in a case of chronic myelocytic leukaemia (CML). Preliminary results correlate well with in vivo estimations obtained by other methods.

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Studie im Rahmen des Assoziationsvertrages EURATOM-GSF für Hämatologie Nr. 031 641 BIAD

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Unterstützt durch die Deutsche Forschungsgemeinschaft: SFB 51/5     

Effects of the Fungicide,S-1358, on General Metabolism and Lipid Biosynthesis in Monilina fructigena

S–1358 (S-n-butyl-S′-p-tert-butylbenzyl n-3-pyridylimidodithiocarbonate) remarkably inhibited growth of Monilinia fructigena at 10 μm, causing excessive branching and distortion of hyphae. Endogenous as well as exogenous respiration was not affected by the toxicant. The incorporations of Uracil-U-¹⁴C and thymine-2-¹⁴C into nucleic acids and protein hydroly-Sate-U-¹⁴C into proteins were only slightly inhibited. Furthermore, S–1358 has no influence on the incorporations of d--glucose-U-¹⁴C and d-glucosamine-1-¹⁴C into cell wall during early incubation periods. On the other hand, although sodium acetate-U-¹⁴C incorporation into total lipids was only moderately suppressed, thin-layer chromatographic separation of labeled lipids revealed that the incorporation into 4-desmethyl sterols was strictly diminished by the toxicant and at the same time the accumulation of radioactivity into 4,4-dimethyl sterols took place. The results presented evidence that S–1358 disturbs the biosynthetic pathways of sterols rather than the other metabolism in M. fructigena.     

Inhibition by 1-beta-D-arabinofuranosylcytosine of the incorporation of N-acetylneuraminic acid into glycolipids and glycoproteins of hamster embryo cells

1-β-D-Arabinofuranosylcytosine which interferes with DNA synthesis in bacteria and mammalian cells and brings about transformation of hamster embryo fibroblasts, has been found to inhibit the incorporation of N-Acetylneuraminic acid into glycolipids and glycoproteins of both normal and transformed hamster embryo cells in tissue culture. Three hours after commencement of treatment (10^?3M ara-C), incorporation of [¹⁴C] thymidine into DNA was inhibited by 95 per cent, while incorporation of [³H] D-glycosamine (precursor of sialic acid) into glycolipids and glycoproteins was inhibited by 85 per cent. At 24 hours, the inhibition of incorporation of the two labelled components was 83 and 80 per cent respectively. In homogenates of both cell types, incorporation of [¹⁴C] N-acetylneuraminic acid was competitively inhibited by ara-CMP. Ara-C was found to have no effect on the incorporation of [¹⁴C] choline into phospholipids of cells grown in tissue culture. These results suggest that interference with DNA synthesis by ara-C may not be the only factor involved in cell transformation by this substance.     

Possible regulation of macromolecular biosynthesis in mammalian cells by a novel dinucleoside polyphosphate (HS3) produced during step-down growth conditions

Shortly after the withdrawal of L-glutamine from the growth medium of Chinese hamster ovary (CHO) cells, the rate of synthesis of a bizarre dinucleoside polyphosphate, HS3, increased by 5- to 6-fold. This elevated rate of synthesis was maintained for six hours before it gradually declined to basal level 22 hours later. The pool size of HS3 increased and decreased coincidentally with rate changes. Withdrawal of L-isoleucine did not affect HS3 biosynthesis. A glycine, adenosine, thymidine (GAT^?) auxotroph of CHO cells accumulated HS3 when adenosine, not glutamine, was withdrawn. Replenishment of either glutamine (“wild type” cells) or adenosine (GAT^? cells) caused an immediate depletion of HS3 intracellularly. When HS3 accumulated in CHO cells, DNA and RNA synthesis decreased and, vice versa. A similar correlation was not seen for protein synthesis. But, inhibition of protein synthesis by either puromycin or cycloheximide, and of RNA biosynthesis by actinomycin D facilitated HS3 depletion in L-glutamine starved cells. Mutant CHO cells that are deficient in purine salvage metabolism, HGPRT^? (hypoxanthine-guanine phosphoribosyltransferase) failed to deplete their accumulated HS3 when fed with hypoxanthine, whereas the “wild type” CHO cells responded accordingly. The available data suggest that HS3 metabolism is connected with de novo and salvage pathways of nucleotide biosynthesis, and may play a crucial role in regulating nucleic acid metabolism in CHO cells under conditions of nutritional stress.     

Nucleotide pools of Novikoff rat hepatoma cells growing in suspension culture. I. Kinetics of incorporation of nucleosides into nucleotide pools and pool sizes during growth cycle

Results from kinetic studies on the incorporation of ³H-5-uridine and ³H-8-adenosine into the acid-soluble nucleotide poor and nucleic acids by Novikoff hepatoma cells (subline N1S1-67) in suspension culture indicate that the uridine transport reaction is saturated at about 100 μM and that for adenosine at about 10 μM nucleoside in the medium, and that above 100 μM simple diffusion becomes the predominant mode of entry of both nucleosides into the cell. The Km of the transport reactions is approximately 1.3 × 10^?5 M for uridine and 6 × 10^?6 M for adenosine. The incorporation of these nucleosides into both the nucleotide pool and into nucleic acids seems to be limited by the rate of entry of the nucleic acid synthesis from the rate of incorporation of nucleosides. Other complicating factors are a change with time of labeling in the relative proporation of nucleoside incorporated into DNA and into the individual nucleotides of RNA, the splitting of uridine to uracil by th ecells, the deamination of adenosine kto inosine and the subsequent cleavage of inosine to hypoxanthine. Various lines of evidence are presented which indicate that the overall nucleotide pools of the cells are very small under normal growth conditions. During growth in the presence of 200 μM uridine or adenosine, however, the cells continue to convert the nucleosides into intracellular nucleotides much more rapidly than required for nucleic acid synthesis. This results in an accumulation of free uridine and adenosine nucleotides in the cells, the maximum amounts of which are at least equivalent to the amount of these nucleotides in total cellular RNA.     

Quinolone effects in the SOS chromotest and in the synthesis of biomacromolecules

The genotoxicity of quinolone antibiotics (ciprofloxacin, enoxacin, nalidixic acid, norfloxacin, ofloxacin, pefloxacin) was studied on the selected mutantE. coli strain PQ37 (SOS chromotest). The genotoxicity was expressed by SOS-inducing potential (SOSIP) values. The highest SOSIP values were found with ciprofloxacin (SOSIP=1967 δIF/nmol), the lowest value was observed with nalidixic acid (SOSIP=0.3 ΔIF/nmol). Similar results were also found with the biosynthesis of nucleic acids, as indicated by incorporation of¹⁴C-adenine into TCA-insoluble fractions ofS. typhimurium cells (ciprofloxacin IC₅₀=0.39, nalidixic acid IC₅₀=400). DNA-damaging effects were tested in the absence of an exogenous metabolizing system.     

The Uptake of Cytokinins by Protoplasts and Root Sections of Brassica campestris

The effect of cytokinins was studied on the incorporation of ¹⁴C-labelled precursors into the nucleic acid fraction of protoplasts isolated from callus or roots of Brassica campestris. Protoplasts from callus and roots took up ¹⁴C-uridine from the incubation medium and incorporated this precursor into the ribonucleic acid fraction during the experimental period of 16 h. Low concentrations of kinetin (10^?8-5 × 10^?6M) did not stimulate the incorporation, and kinetin inhibited this process at higher concentrations (5 × 10^?5M). This result led to an investigation on the uptake of cytokinins by protoplasts of roots. In contrast to a rapid uptake of radio-actively labelled adenine and uridine. protoplasts from roots took up only small amounts of labelled kinetin. zeatin, zeatin riboside and zeatin nucleotides from the incubation medium. Root sections took up far more adenine and kinetin than protoplasts from roots. The ratio between the amount of kinetin taken up and applied was much higher for the sections than for protoplasts, indicating that intact root cells took up kinetin far more rapidly than protoplasts. It is suggested that the plasmalemma and cell wall play an essential role in the uptake of cytokinins or that the differences in the uptake rates are related to differences between the rates of metabolism of cytokinins in root sections and in protoplasts.     

Metabolic fate of guanosine in higher plants

The aim of the present study was to investigate the metabolic fate of guanine nucleotides in higher plants. The rate of uptake of [8-¹⁴C]guanosine by suspension-cultured Catharanthus roseus cells was more than 20 times higher than that of [8-¹⁴C]guanine. The rate of uptake of [8-¹⁴C]guanosine increased with the age of the culture. Pulse-chase experiments with [8-¹⁴C]guanosine revealed that some of the guanosine that had been taken up by the cells was converted to guanine nucleotides and incorporated into nucleic acids. A significant amount of [8-¹⁴C]guanosine was degraded directly to xanthine, allantoin and allantoic acid, with the generation of ¹⁴CO₂ as the final product. The rate of salvage of [8-¹⁴C]guanosine for the synthesis of nucleic acids was highest in young cells, while the rate of degradation increased with the age of the cells. In segments of roots from Vigna mungo seedlings, nearly 50% of the [8-¹⁴C]guanosine that had been absorbed over the course of 15 min was recovered in guanine nucleotides. A significant amount of the radioactivity in nucleotides became associated with nucleic acids and ureides during ‘chase’ periods. In segments of young leaves of Camellia sinensis, [8-¹⁴C]guanosine was initially incorporated into guanine nucleotides, nucleic acids, theobromine and ureides, and the radioactivity in these compounds was transferred to caffeine and CO₂ during a 24-h incubation. Our results suggest that guanosine is an intermediate in the catabolism of guanine nucleotides and that it is re-utilised for nucleotide synthesis by ‘salvage’ reactions. Guanosine was catabolised by the conventional degradation pathway via xanthine and allantoin. In some plants, guanosine is also utilised for the formation of ureide or the biosynthesis of caffeine.     

Synthetic Analogues of the Termite Trail-following Substance

The effect of tripropyltin chloride (TPT) on some functional reactions in E. coli was investigated. The inhibition on respiration and protein, DNA and RNA syntheses were examined in vivo. Oxygen consumption by E. coli cells was scarcely inhibited even at the concentration of 30 µg/ml TPT. The incorporations of ¹⁴C-labeled amino acids into protein fraction were inhibited. Especially, in the case of l-leucine, it was inhibited 60% even at 10 µg/ml TPT. Both incorporations of ¹⁴C-adenine into DNA and RNA fraction were inhibited 50–60% at 20 µg/ml TPT. RNA polymerase was prepared from E. coli cells and the effect of organotin compounds on the enzyme activity was examined. Organotin compounds inhibited the enzyme activity only at high concentrations (5-10mm). and dialkyltin chlorides which possess no antimicrobial action showed the inhibition more intensely than trialkyltin chlorides. The effect on membrane-bound ATPase was also examined in vitro. We found that TPT has high inhibitory action on membrane-bound ATPase. However, it slightly inhibited the activity of ATPase separated from membrane.     

Stimulation of Growth and Nucleic Acid Biosynthesis at Low Concentration of Abscisic Acid in Tissue Culture of Spinacia oleracea

The effect of abscisic acid on growth, ultrastructure and nucleic acid biosynthesis was studied in tissue culture of spinach (Spinacia oleracea L.). Low concentration (0.01 mg l^?1) of abscisic acid increased fresh and dry weight of calluses, whereas 1.0 mg l^?1 was inhibitory. The stimulating effect was observed only in the presence of a relatively high concentration of kinetin (1 mg l^?1). The inhibitory effect was partly overcome by the same kinetin concentration. The low concentration of abscisic acid probably accelerated the induction of callus growth after subculture and stimulated cell division in the exponential phase of growth. Electron microscopy showed the presence of numerous polysomes and rough endoplasmic reticulum in callus cells grown at the stimulating abscisic acid concentration. Control cells and cells at the inhibitory concentration had slightly hyaline cytoplasm and were more vacuolated. Incubation of callus tissue with ³²P in the presence of stimulating concentration of abscisic acid showed a significant increase in the rate of biosynthesis of all nucleic acid classes after 8 h, whereas inhibitory concentration produced a decrease in ³²P incorporation. However, when the tissue was grown in the presence of abscisic acid for 20 days, both concentrations decreased the rate of nucleic acid biosynthesis, as compared to the controls.     

Studies on Deoxyribonucleotide Synthesis in Vicia faba

The incorporation of uniformly labelled [¹⁴C] cytidine into the nucleic acids was studied in root tips of Vicia faba. Cytidine was found to be incorporated into RNA and DNA and the specific activities of the individual mononucleotides were deter- mined. The pyrimidine nucleotides were degrade and the ratio between the specific activity of the pentose and the specific activity of the base was determined for each nucleotide. CMP of RNA and deoxy CMP of DNA bad almost the same pentose: base ratios as The cytidine added to the incubation medium. It was concluded that the administered cytidine or a derivative of it was reduced to the corresponding deoxycytidine compound without breakage of the bond between pentose and base. [¹⁴C)-cytidine was transformed to UMP of RNA with some loss of radioactivity from the pentose and had almost the same pentose: base ratio as deoxy TMP of DNA. This indicates that the formation of thymidine phosphates involved The reduction of a uridine compound. Furthermore the incorporation of ¹⁴C-labelled thymidine, deoxyadenosine and deoxyguanosine into DNA was studied. Deoxyguanosine was found to be incorporated only to a slight extent. This finding has been discussed in relation to previous results.     

Structure of Daunomycin; X-ray Analysis of N-Br-Acetyl-Daunomycin Solvate

THE antibiotic daunomycin was discovered and studied by Di Marco and co-workers^1–5 who found it to have cytotoxic and antimitotic activity. Extensive chemical work by Arca-mone and co-workers^6–9 has established the total absolute configuration as in Fig. 1, which gives the formula of the N-Br-acetyl derivative. Daunomycin interferes with nucleic acid metabolism in both mammalian¹⁰ and bacterial¹¹ cells and the formation of a complex between daunomycin and nucleic acids has been studied^12–16. The nature of the chemical binding between antibiotics which affect ribonucleic acid synthesis and DNA has been discussed¹⁶ and it has been suggested that the amino as well as either quinone^17,18 or hydroxyl groups of the chromophore are responsible for hydrogen bonding to the DNA helix. An understanding of this effect is important as the binding of daunomycin to DNA is most likely responsible for the biological activity of this antibiotic. To determine the detailed stereochemical features of daunomycin, the relative orientation of the sugar ring to the aglycone moiety and the nature of the hydrogen bonding in the solid state, we began X-ray crystallographic studies.     

Nutrient media for plant-parasitic nematodes. VI. Nucleic acids content and nucleotide synthesis in Aphelenchoides rutgersi

The nucleic acids content of Aphelenchoides rutgersi, Hooper and Myers, was 0.9% DNA and 2.6% RNA dry weight. The DNA contained 29.5% adenine, 29.3% thymine, 22.5% guanine, and 18.8% cytosine, while the RNA was composed of 22.8% adenine, 23.0% uracil, 31.4% guanine, and 22.9% cytosine on a molar basis.The nematodes needed folic acid for reproduction regardless of the presence or absence of nucleic acid supplements in the culture medium. This was shown by including aminopterin, a folic acid antagonist in the culture medium. A 2-hr incubation of nematodes with glycine-¹⁴C (U) and orotic-5-³H acid resulted in the incorporation of ³H-label into both DNA and RNA. Only the RNA fraction contained a significant amount of ¹⁴C-label. When this RNA was fractionated, the adenine and guanine accounted for the ¹⁴C-label, while cytidylic and uridylic acids contained the ³H-label, thereby demonstrating purine and pyrimidine synthesis by A. rutgersi. The incorporation of orotic acid into the pyrimidines was 8 times higher than that of glycine into purines.