Phosphodiester bonds between polypeptides and chromosomal DNA

Polypeptides co-purifying with DNA in alkali are covalently bound to DNA. DNA purified by treatment with alkali, sodium dodecyl sulphate and phenol absorbed 125I under conditions designed to radioiodinate exclusively tyrosine and histidine in peptides. A significant amount of the absorbed 125I remained associated with DNA during treatment with phenol as well as during precipitation with ethanol from neutral and alkaline solutions. However, after prolonged digestion with proteinase K, most of the radiolabelled material could be removed from 125I-treated DNA. Further treatment with a second protease (Pronase) released no larger fraction of the 125I label. The residual radiolabelled material could be precipitated together with DNA by ethanol and it remained associated with DNA also in the presence of alkali (95 degrees C), acid (37 degrees C) and hydroxylamine (37 degrees C). In contrast, radiolabelled peptides were released from DNA by treatment with hot piperidine (10% at 95 degrees C) and by agents that hydrolyse peptides and modify DNA, e.g. strong acid (95 degrees C) and formic acid/diphenylamine. The radiolabelled peptides, once released from DNA by these chemical methods, could be further cleaved by Pronase. This shows that the residual DNA/peptide complex isolated after prolonged protease digestion is protease-resistant unless it is cleaved or otherwise modified by harsh chemical treatment. The linking groups between deoxynucleotides and the radiolabelled residual peptides could be isolated by digestion of DNA in the DNA/peptide complex. Radiolabelled peptides could be released from this linking group material by phosphodiesterases, indicating the involvement of phosphodiesters in the linking groups.

Enhancement of specific nitrogenase activity in Azospirillum brasilense and Klebsiella pneumoniae, inhibition in Rhizobium japonicum under air by phenol

Specific nitrogenase activity in Azospirillum brasilense ATCC 29145 in surface cultures under air is enhanced from about 50 nmol C2H4 X mg protein -1 X h-1 to 400 nmol C2H4 by the addition of 1 mM phenol. 0.5 and 2 mM phenol added increase the rate 5-fold and 4-fold. This enhancement effect is observed only between 2 and 3 days after inoculation, with only a small reduction of the growth of the cells by the phenol added. In surface cultures under 1% O2, nitrogenase activity is slightly reduced by the addition of 1-0.01 mM phenol. Utilization of succinate is enhanced during the period of maximum enhancement of nitrogenase activity by 60% by addition of 1 mM phenol. The cells did not produce 14CO2 from [U-14C] phenol, neither in surface cultures nor in liquid cultures and less than 0.1% of the phenol was incorporated into the cells. A smaller but significant enhancement of nitrogenase activity by about 100% in surface cultures under air was found with Klebsiella pneumoniae K 11 after addition of 1 mM phenol. However, in Rhizobium japonicum 61-A-101 all phenol concentrations above 0.01 mM reduced nitrogenase activity. With 1 mM phenol added activity was reduced to less than 10% with no effect on the growth in the same cultivation system. With this Rhizobium japonicum strain significant quantities of phenol (25 mumol in 24 h by 2 X 10(12) cells) were metabolized to 14CO2, with phenol as sole carbon source. With Azospirillum brasilense in liquid culture under 1% and 2% O2 in the gas phase, no enhancement of nitrogenase activity by phenol was noticed.

A comparison of diazepam and phenoperidine in premedication for upper gastrointestinal endoscopy: a randomized double blind controlled study

A variety of agents are used as premedication for upper gastrointestinal endoscopy (U.G.E.). To our knowledge, no double blind studies have been performed to compare their value. In this study phenoperidine (2 mg i.v.) was compared with diazepam (t mg i.v.) in 200 consecutive patients undergoing elective U.G.E. The study was randomized and double blind in regard to both endoscopists and patients. All patients were given atropine (0.4 mg i.v.) and a throat spray with 2% amethocaine. Patients who needed supplemental medication were given diazepam and excluded from final analysis. A graded questionnaire was recorded by endoscopists and patients after U.G.E., and a further anonymous questionnaire was returned by patients four days later. Statistical analysis revealed that phenoperidine was superior at facilitating intubation and providing more relaxation as judged by the endoscopist. Patient questionnaires, four days after U.G.E., indicated less distress during intubation and examination with phenoperidine. Nausea, vomiting, amnesia and phlebitis were uncommon after either phenoperidine or diazepam.

Non-random distribution of N-methyl-N-nitrosourea sensitive sites in a eukaryotic genome

DNA released from Ehrlich ascites cells by lysis in the presence of 50 microgram X ml-1 of proteinase K contains long alkali-stable strands in the order of 50-100 X 10(6) daltons. In contrast, DNA released in the presence of 6 mg X ml-1 of autodigested pronase is significantly nicked. According to sedimentation rates the number of internal ends liberated during this procedure is 24/200 X 10(6) daltons. The number of alkali-labile sites introduced into DNA by incubation of Ehrlich ascites cells with 1 nM of N-methyl-N-nitrosourea (MNU) followed by cell lysis in the presence of 50 microgram X ml-1 of proteinase K and alkali-denaturation is 16.6/200 X 10(6) daltons. From this one should expect that denatured DNA released from cells pretreated with 1 mM of MNU which are subsequently lysed with 6 mg X ml-1 of pronase would have about 40 single-strand breaks/200 X 10(6) daltons. However, denatured DNA strands released by 6 mg X ml-1 of pronase either from MNU-treated or untreated cells cannot be separated by centrifugation through alkaline sucrose gradients. This phenomenon could be explained by a non-random distribution of MNU-inducible alkali-labile sites of DNA in vivo.

Fistula between left coronary artery and superior vena cava

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Size of native and denatured DNA of Ehrlich ascites tumour cells isolated in the presence of different protease concentrations

Native DNA molecules isolated either in the presence of 50 micrograms x ml(-1) of proteinase K (PK-DNA) or in the presence of 6 mg x ml(-1) autodigested pronase (PRO-DNA) are about equal in size. Since shear forces were avoided as far as possible during the isolation procedure, the largest molecules found were longer than 100 microns. The average length of the traced molecules was 34.2 microns for PK-DNA and 29.7 microns for PRO-DNA. In contrast to PK-DNA the length of PRO-DNA molecules undergoes a dramatic change during denaturation. The average contour length of a denatured PRO-DNA molecules is only 6.9 microns. This reduction in length cannot be explained by shrinkage due to changes in ionic strength, pH and the effect of denaturing agents. Moreover, PK-DNA identically denatured was not dramatically changed in size. From this it must be concluded that PRO-DNA contains more internal ends than PK-DNA. This conclusion is supported by the results indicating that PRO-DNA is much more sensitive to nuclease S1 than PK-DNA. The results are consistent with previously published biochemical data suggesting that chromosomal DNA is 'nicked' or 'gapped' in a protease-catalyzed reaction at distinct protease-sensitive sites.

Cell density dependent DNA replication in Ehrlich ascites tumour cells

DNA replication of Ehrlich ascites tumour cells was investigated in suspensions with different cell densities by incorporation in vitro of tritiated thymidine and alkaline sucrose gradient analysis of the newly formed DNA. It is demonstrated that the incorporation of [3H]thymidine and chain growth of newly made DNA decreases with increasing cell density. The inhibition of DNA synthesis observed at high cell densities can be prevented if diffusible substances are removed by incubating the cells in dialysis tubes. This indicates that the changes in DNA synthesis are caused by diffusible inhibitors released from the tumour cells.

Root exudates in relation to growth and nitrogenase activity of Rhizobium japonicum

Root exudates of cowpea and soybean were collected in aerated water cultures. The ability of these exudates to support nitrogenase activity of R. japonicum was studied on defined media. When a complete nitrogenase-inducing medium was supplemented with concentrated root exudate, there was an increased nitrogenase activity. When the cowpea root exudate was substituted for glutamine or sodium succinate in the medium, nitrogenase activity was not detected. Growth was good when the root exudate was substituted for sodium succinate but was poor when the exudate replaced glutamine. There was nitrogenase activity in R. japonicum when the cowpea root exudate was substituted for arabinose in the 20E medium. Gas chromatographic analyses of cowpea root exudates revealed that ribose, arabinose, glucose, and sucrose were the main constituents. The significance of this finding in the asymbiotic nitrogen fixation by Rhizobium spp. is discussed.

Screening for mutants of Rhizobium japonicum with defects in nitrogen fixing ability

Mutants of Rhizobium japonicum with reduced ex planta nitrogenase activity could be isolated with high frequency by direct screening of ultra-violet mutagenized bacteria growing as spots on the surface of an appropriate agar medium permitting derepression of nitrogenase synthesis. Small glass chambers fitted with a serum cap were pushed into the agar around each spot of growth, forming a small enclosed gas space which was made to 10% acetylene, permitting assessment of nitrogenase activity by the acetylene reduction test. Four mutants were isolated from a total of 305 screened spots. Two mutants had almost no ex planta activity, one of which had no symbiotic activity despite normal nodulation (ineffective), the other had only somewhat reduced activity symbiotically. Two other mutants with less than half wild-type activity ex planta were normal in symbiosis.

Internucleotide protein linkers in Ehrlich ascites cell DNA

DNA from Ehrlich ascites tumor cells is nicked or gapped by a reaction which is induced by proteases such as autodigested pronase, proteinase K, trypsin, chymotrypsin and subtilisin. The cleavage of the protease-sensitive sites is inhibited by protease inhibitors. The nicks or gaps induced by proteases can be demonstrated by nuclease S1 sensitivity of native DNA and by a change of the sedimentation rate of alkali-denatured DNA. The limit size of denatured DNA released after optimal protease treatment is 8.5 x 10(6) daltons (27 kilo bases). The molecular weight of the native DNA pieces released after nuclease S1 degradation of DNA containing the protease-induced nicks or gaps is in the same order indicating that the protease-sensitive sites are alternatively arranged on the opposite DNA strands at an average distance of 13.5 kilo base pairs. Since the protease-induced nicks or gaps in phosphatase-treated DNA are not attacked by Escherichia coli polymerase I, one or both ends liberated by the protease treatment must be blocked by a material other than phosphate groups. The results are most compatible with peptide/protein linkers joining adjacent single-strand DNA subunits. Alternative explanations such as alkali-stable RNA linkers, protein-protected RNA linkers, site-specific nuclease contaminations in the protease preparations or cellular nucleases activated by the protease treatment are eliminated by the results presented in this paper.

Development of nodules of Glycine max infected with an ineffective strain of Rhizobium japonicum

Bacteroids in ineffective (nitrogenase negative) nodules of Glycine max, infected with Rhizobium japonicum 61-A-24, as compared to those in effective nodules are characterized by reduced specific activities of alanine dehydrogenase to 15%, of 3-hydroxybutyrate dehydrogenase to 50%, and an increase of glutamine synthetase to 400%. In the plant cytoplasm of ineffective nodules, glutamine synthetase activity is reduced to 10-30%, glutamate dehydrogenase to 50-70%, and the aspartate aminotransferase and alanine aminotransferase are enhanced to 120-200%, depending on the age of the nodules. The total pool of soluble amino acids is reduced to 52 μmol per g nodule fresh weight, as compared to 186 μmol in effective nodules, with a replacement of asparagine (42 mol% of the amino acids) by an unknown amino compound. This compound is absent in nitrogenase, repressed and derepressed, free-living Rhizobium japonicum cells and in the uninfected root tissue. In nitrogenase derepressed, as compared to the repressed free-living cells of Rhizobium japonicum 61-A-101, arginine shows the most obvious change with a reduction to less than one tenth. The ultrastructure of the ineffective nodule is different from the effective organ even in the early stages. The membrane envelopes of the infection vacuoles are decomposing in heavily infected cells within 18 to 20 d after infection. In lightly infected cells very large vacuoles develop with only a few bacteroids inside. No close associations of cristae-rich mitochondria with amyloplasts are observed as in effective nodules. The uninfected cells keep their large starch granules even 40 d after infection. Some poly-β-hydroxybutyrate accumulation in the bacteroids is observed but only in the early stages, and it is almost absent in old nodules (40 d). At this age the infected cells are obviously compressed by uninfected cells, whereas in effective nodules with nitrogenase activity and leghaemoglobin formation, the infected cells have a much higher osmotic pressure than the neighbouring uninfected cells.

Analysis of the most tightly bound proteins in eukaryotic DNA

DNA isolated by procedures generally considered to be most efficient for purifying DNA still contains detectable peptide components. The characteristics of this material and the stability of its linkage to DNA were investigated: DNA released from [35S]methionine-labelled cells by SDS in the presence of proteases contains a significant amount of 35S label which is not removed by additional treatment with proteases and phenol and which cosediments and cobands together with DNA on alkaline gradients. Furthermore, some peptide material which is copurified with native DNA and which remains complexed with DNA after alkali treatment can be labelled with 125I and analyzed on SDS-polyacrylamide-gels. The amino acid analysis of hydrolysates of purified DNA gives a rough estimate of the amount of the peptide material which is copurified with DNA. The results indicate that distinct proteins between 54 000 and 68 000 daltons in size are not removed from DNA by phenol, proteases, alkali or by any combination of these treatments. They can only be isolated by degradation of DNA. This extreme stability of the DNA-protein linkage indicates that these proteins are not merely contaminants which are difficult to eliminate but are rather covalently or otherwise bound (alkali-stable) to DNA. The size of these proteins and the stability of their linkage to DNA suggests that they are related to the class of non-histone proteins which are thought to be involved in chromatin structure e.g. by keeping DNA in a supercoiled state. Other possible functions are discussed.

A simple method for the separation of tissue-cultured plant cells from unbound bacteria: a demonstration of acquired affinity for bacteria by cells of soy bean

Tissue-cultured cells of soy bean, grown in liquid medium and then transferred to an agar substratum in so-called tissue chambers, showed an affinity for the binding of applied bacteria (Klebsiella pneumoniae). This binding, which became greater as the plant cells remained on the agar for up to 10 days, was manifested as an increasing resistance of the bacteria to be washed from the plant cells in a standard, gentle and reproducible procedure devised for this purpose. The number of bacteria firmly bound to the cells was determined by the use of 32P-labelled bacteria and was largely independent of the concentration of bacteria in the suspension applied to the tissue-cultured cells.

Differentiation of Rhizobium japonicum, III. Inhibition of nitrogenase derepression by chloramphenicol and rifampicin concentrations, not inhibiting growth

Development of nitrogenase (40--140 nmol C2H4.mg protein-1.h-1) in Rhizobium japonicum 61-A-101 after transfer to special culture conditions (medium 20 P, 2% O2, 10% CO2, 88% N2 in the gas phase) is inhibited by chloramphenicol (6 X 10(-4)--10(-3) M) and by rifampicin (10(-5) M). These concentrations do not inhibit the slow growth of the cells under these conditions with a doubling time of the cell protein and living cell number of 3--5 d. Nitrogenase activity of previously derepressed cells is not inhibited by chloramphenicol. Growth of the cells under air in yeast extract-mannitol-glycerol medium (8 h doubling time) is affected significantly more by chloramphenicol (2.5 X 10(-4) M) than growth under nitrogenase derepressed culture conditions.

Differentiation of Rhizobium japonicum. II. Enzymatic Activities in Bacteroids and Plant Cytoplasm during the Development of Nodules of Glycine max

Phytotron grown plants of Glycine max var. Caloria infected with Rhizobium japonicum 61-A-101 under controlled conditions as 14 d old seedlings develop a sharp maximum of nitrogenase activity of 13 ± 3 nmol C2H4 · h-1 · mg nodule fresh weight-1 19 d after infection, followed by a long period of reduced activity (3 -5 nmol) between 30 and 45 days after infection. A higher maximum activity (18 nmol C2H4 · h-1 · mg nodule-1, lasting 7 days was found in Glycine max var. Mandarin, with a similar peroid of low activity (3 - 4 nmol) following, between 35 and 50 d after infection. Nitrogenase activity in the varieties infected with Rhizobium japonicum strain 3I1 b 85 is very similar. In both varieties, the leghaemoglobin continues to increase (3 fold) after the maximum nitrogenase activity is reached and starts to decline only after 35 to 40 d.

Specific activities of the three enzymes aspartate aminotransferase (E.C.2.6.1.1.), glutamate dehydrogenase (E.C.1.4.1.2.) and alanine aminotransferase (E.C.2.6.1.2.) in the plant cell cyto­plasm are changing very similarly to nitrogenase activity in the bacteroids, whereas the specific activities of the three enzymes in the bacteroids decrease only very slightly between 19 and 45 d. For these 3 enzymes the specific activity in the bacteroids during the phase of maximum nitrogenase activity is only 20 - 40% of the specific activity in the cytoplasm.

A constant low activity (0.350 units) of glutamine synthetase (E.C.6.3.1.2.) is found in bacteroids from 19 to 45 d old nodules, whereas the specific activity in the plant cytoplasm increases from about 1.2 units at 19 d to more than 6 units at 45 d. The specific activity of GOGAT (E.C.1.4.13.) in bacteroids is 2 - 3 times higher than in the plant cell cytoplasm and increases slightly. Alanine dehydrogenase (E.C.1.4.1.1.) and 3-hydroxybutyrate dehydrogenase (E.C.1.1.1.30.) activities in bacteroids increase between 19 and 35 d after infection by a factor of 2 - 3. In 35 - 45 d old nodules, the specific activity of aianine-dh in bacteroids of the same Rhizobium japonicum strain (61-A-101) from plant var. Caloria is significantly smaller than in bacteroids from plant var. Mandarin, whereas for 3-hydroxybutyrate-dh the activity in bacteroids from var. Caloria is enhanced compared to bacteroids from var. Mandarin.

Differentiation of Rhizobium japonicum, I. enzymatic comparison of nitrogenase repressed and derepressed free living cells and of bacteroids

Derepressed free living cells of Rhizobium japonicum strain 61-A-101 with leucine as single nitrogen source develop a maximum nitrogenase activity of 180 nmol C2H4.mg protein -1.H-1 in liquid culture under 2% 2% O2 in the gas phase. Only 10% of this activity is found with no oxygen in the gas phase during a 90 min incubation period. The maximum activity under 2% oxygen in the gas phase is unaffected by addition of 1-100 mM NH+4 and by addition of low concentrations of glutamine (0.36-1.44 mM). Specific activities of alanine dehydrogenase (E.C. 1.4.1.1.) asparatate aminotransferase (E.C. 2.6.1.1.) and, with much lower activities, of GOGAT (E.C. 1.4.1.13) in nitrogenase active free living cells are more similar to bacteroids than to nitrogenase repressed free living cells from liquid culture. The activities in nitrogenase repressed cells were about 50% lower. Glutamine synthetase (E.C. 6.3.1.2.) activity in bacteroids and in nitrogenase active cells were also similar, but only about 25-30% of that found in nitrogenase repressed Rhizobium japonicum cells.

Differentiation of nodules of Glycine max : Ultrastructural studies of plant cells and bacteroids

Plants of Glycine max var. Caloria, infected as 14 d old seedlings with a defined titre of Rhizobium japonicum 3Il b85 in a 10 min inoculation test, develop a sharp maximum of nitrogenase activity between 17 and 25 d after infection. This maximum (14±3 nmol C2H4 h(-1) mg nodule fresh weight(-1)), expressed as per mg nodule or per plant is followed by a 15 d period of reduced nitrogen fixation (20-30% of peak activity). 11 d after infection the first bacteroids develop as single cells inside infection vacuoles in the plant cells, close to the cell wall and infection threads. As a cytological marker for peak multiplication of bacteroids and for peak N2-fixation a few days later the association of a special type of nodule mitochondria with amyloplasts is described. 20 d after inoculation, more than 80% of the volume of infected plant cells is occupied by infection vacuoles, mostly containing only one bacteroid. The storage of poly-β-hydroxybutyrate starts to accumulate at both ends of the bacteroids. Non infected plant cells are squeezed between infected cells (25d), with infection vacuoles containing now more than two (up to five) bacteroids per section. Bacteroid development including a membrane envelope is also observed in the intercellular space between plant cells. 35 d after infection, more than 50% of the bacteroid volume is occupied by poly-β-hydroxybutyrate. The ultrastructural differentiation is discussed in relation to some enzymatic data in bacteroids and plant cell cytoplasm during nodule development.

Isolated retinal hemorrhages associated with oral contraceptives

Seven patients had isolated retinal hemorrhages without other systemic or ocular disease in a six-year period. Six patients were females, of whom five were taking oral contraceptives. The number of patients taking contraceptives and the fact that one patient had a similar episode earlier during pregnancy suggested a hormonal etiology. In the two patients we examined, we concluded that direct hormonal action causing vascular wall lesions was probably responsible for the pathology.

Pseudophakic pupillary-block glaucoma

Four cases of iris-supported pseudophakic pupillary-block glaucoma were presented. Pupillary-block glaucoma is the first postoperative complication seen following the implantation of an intraocular lens, and in our series occurred at an incidence of 3-8%. A short review was made of pupillary-block glaucoma with all types of intraocular lenses, with emphasis on the iris-supported lens. The role of inflammation, haemorrhage, and vitreous and lens material in obstructing aqueous flow at the pupil and peripheral iridectomy site was emphasised. Pitfalls in the diagnosis and management of this condition were reviewed. Methods of prevention and treatment were reviewed with emphasis on early mydriasis, along with carbonic anhydrase inhibitors and hyperosmotic agents as a primary medical treatment. Iridectomy, laser iridotomy, or transfixation of the iris was mentioned as a surgical treatment.

Discrimination of Rhizobium japonicum, Rhizobium lupini, Rhizobium trifolii, Rhizobium leguminosarum and of bacteroids by uptake of 2-ketoglutaric acid, glutamic acid and phosphate

Rhizobium strains (one each of Rh. japonicum, Rh. lupini, Rh. leguminosarum) take up 2-ketoglutaric acid in general much faster and from lower concentrations in the medium than strains of Escherichia coli, Bacillus subtilis and Chromobacterium violaceum. A strain of Enterobacter aerogenes, however, is more similar to some Rhizobium strains. The same strains of Rhizobium take up also phosphate much faster and from lower concentrations than the other bacteria tested. 4 strains of Rh. lupini proved to be significantly different from 4 strains of Rh. trifolii in taking up L-glutamic acid from three to ten times lower concentration within 5 h. A similar difference was noticed between 5 strains of Rh. leguminosarum and 2 strains of Rh. japonicum for the uptake of 2-ketoglutaric acid and of L-glutamic acid. Isolated bacteroids from nodules of Glycine max var. Chippeway have a reduced uptake capacity for glutamic acid and for 2-ketoglutaric acid during the first 10-12 h, but reach the same value after 24 h as free living Rh. japonicum cells. The differences in the uptake kinetics are independent of cell concentration. The group II Rhizobium strains (Rh. japonicum and Rh. lupini, slow growing Rhizobium) are characterized by a rapid uptake of glutamic acid to a low remaining concentration of 1-3 X 10(-7) M and an uptake of 2-ketoglutaric acid to a remaining concentration of 2-5 X 10(-7) M. The group I Rhizobium strains (Rh. trifolii and Rh. leguminosarum, fast growing Rhizobium), can be characterized by a much slower uptake of both substances with a more than ten times higher concentration of both metabolites remaining in the medium after the same time.

Synthesis and biological activity of pyrazolo[3,4,-d]pyrimidine nucleosides and nucleotides related to tubercidin, toyocamycin, and sangivamycin

The 6-aza analogues of toyocamycin and sangivamycin were prepared as potential cytotoxic agents. The toyocamycin analogue (4-amino-1-(beta-D-ribofuranosyl)pyrazolo[3,4-d]pyrimidine-3-carbonitrile) could not be obtained directly from its O-acetylated precursor but was accessible via 4-amino-1-(beta-D-ribofuranosyl)pyrazolo[3,4-d]pyrimidine-3-thiocarboxamide. The identity of the nitrile was verified by its ultraviolet, infrared, and mass spectra, and by its conversion to the corresponding 3-carboxamide and thiocarboxamide when treated with water or hydrogen sulfide, respectively. Bioassay of the synthetic compounds in comparison with 4-amino-1-(beta-D-ribofuranosyl)pyrazolo[3,4-d]pyrimidine (6-azatubercidin) and 4-amino-2-(beta-D-ribofuranosyl)pyrazolo[3,4-d]pyrimidine revealed that the 3-thiocarboxamido derivative was more cytotoxic to the growth of mouse fibroblasts than 6-azatubercidin, effecting killing of 3T6 cells at less than or equal to 1 mug/ml. 4-Amino-1-(beta-D-ribofuranosyl)pyrazolo[3,4-d]pyrimidine (but not its 2-ribofuranosyl isomer) was shown to act as a substrate for adenosine deaminase from calf intestinal mucosa with an apparent Km of 125 (vs. 20 for adenosine) and the corresponding 5'-diphosphate of 6-azatubercidin was polymerized by polynucleotide phosphorylase (Micrococcus luteus) in the presence of Mn2+ to afford a homopolymer and copolymers with adenosine. The copolymers directed the binding of [3H]lysyl-tRNA to the A-site of ribosomes from Escherichia coli, but could not be used for the synthesis of polylsine in a cellfree system. The copolymer consiting of adenosine and 6-azatubercidin in a 2:1 ratio was found to form a 1:1 complex with poly(uridylic acid) at 4degreesC.

Adsorption and selection of rhizobia with ion-exchange papers

Ion exchange papers were used to study the adsorption of 32P-labelled rhizobia on defined surfaces. Two strains of Rhizobium japonicum and one each of R. leguminosarum and R. lupini were compared with Escherichia coli and Bacillus subtilis. The ratio of adsorption to strong and to weak acid papers/strong and weak basic papers was consistantly higher for all rhizobial strains compared to the other bacteria. The process of desorption by increasing the ion-concentration causes about 35% desorption between 0.02 and 0.1 M MgCl2, however, an increase to 1 M does not desorb more labelled Rhizobium japonicum or E. coli cells. The ratio of adsorbed cpm to colony formers, desorbed by 0.1 M NaCl was similar with Rhizobium japonicum for all six ion exchange papers. For E. coli this ratio varied widely for the different papers. The selection of Rhizobium against a more closely related bacterium by this adsorption/desorption procedure was demonstrated with mixed cultures of Rhizobium japonicum and Chromobacterium violaceum giving a more than 80 fold enrichment of the former. Rhizobium japonicum cells, ad/desorbed from all ion exchange papers kept their infectivity and formed nodules on Glycine max with an activity of 20-40 nM C2H4-hr(-1)-mg nodule(-1). A desorption of Rhizobium japonicum from soybean roots also occurred by increasing the ion concentration. 2-3 times as many cells were removed in this way compared to washing with water.

On the "activation" of cytokinins

A number of cytokinin analogs containing modifications in the heterocyclic moiety were prepared. These compounds were tested for activity as cytokinins and anticytokinins in the tabacco bioassay and the results were used to determine whether any position(s) of the heterocyclic nucleus of cytokinins may require derivatization as part of an over-all "activation" process. 3-substituted 4-alkylaminopyrazolo [3,4-d]pyrimidines and 4-alkylaminopyrrolo[2,3-d]pyrimidines, for example, have (substituted) carbon rather than nitrogen atoms at positions 3 and 5, respectively (analogous to position 7 in purines) and would be predicted to be metabolically stable at these positions. The finding that these compounds had cytokinin activity suggested that modification at the metabolically stable positions. The finding that these compounds had cytokinin activity suggested that modification at the metabolically stable position, and by extension at position 7 in cytokinin analogues which are purines, is not a prerequisite for the expression of cytokinin activity. Similar consideration of other heterocyclic analogs which have cytokinin activity suggests that the active form of a cytokinin can be the exogenous compound itself. Certain structural analogs of cytokinins were found to inhibit the growth of tobacco callus promoted by 6-(3-methyl-2-butenylamino)purine. These compounds were studied as potential cytokinin antagonists, i.e. having activity analogous to the 7-alkylamino-3-methylpyrazolo[4,3-d]pyrimidines (Hecht, S. M., 2068-2610; Skoog, F., Schmitz, R.Y., Hecht, S.M., and Bock, R. M. (1973) Phytochemistry 12, 25-37). The activity of these compounds is discussed and criteria are proposed to distinguish between those species which are specific anticytokinins and those which otherwise inhibit growth.

Nitrogen fixing activity in Rhizobium japonicum separated from plant cell cultures

Induced by soy bean tissue cultures in socalled "tissue chambers", Rhizobium japonicum str. 61-A-96 developed nitrogenase activity separated from the plant cells. The activity proceded for 48 h with a rate of 1 X 10(-8) nmol C2H4h-1 cell-1, which is about 6% of the activity measured for bacteroids from Rhizobium japonicum in nodules of Glycine max.

Deficiency of joining of Okazaki-type fragments in absence of cellular protein synthesis

The dependence of integration of newly formed DNA chain ( less than 10 S) into larger DNA on concomitant protein synthesis was studied in a special cellular system. Exponentially growing Ehrlich ascites tumor cells in vivo show decreasing rated and finally complete cessation of protein and DNA synthesis upon transfer into an isotonic but non-nutritive environment (Hanks' balanced salt solution). Both protein and DNA synthesis is stimulated in these cells for a period of 30 min when they are placed into fresh Hanks' balanced salt solution; however, stimulation of protein synthesis is completely prevented in Hanks' balanced salt solution containing cycloheximide. This system allowed us to investigate the formation and fate of newly formed DNA chains ( less than 10 S) in dependence of protein synthesis. Analysis of DNA produced in [3H]thymidine pulses showed that DNA chains smaller than 18 S were still formed during the phase of totally delayed protein synthesis and in the presence of cycloheximide, but they were not converted into DNA molecules sedimenting faster than 18 S under these conditions. Stimulation of protein synthesis for a period of 30 min allowed the short DNA pieces to be chased into larger DNA 30 min post stimulation of protein synthesis. The results clearly indicate that DNA chain growth, by sealing of DNA chains smaller than 18 S, is strongly dependent of concomitant protein synthesis. Direct chain elongation by addition of new deoxyribonucleotides is less dependent on concomitant cellular protein synthesis.

The Separation of 32Silicon from Contaminating 3H and 60Co by Incorporation into Diatoms

32Si (β-. 0,1 MeV, half life about 280 years) has been used, as for as we are aware, for the first time in bio­ logical and biochemical experiments . 32Si was incorporated by the pathway of the silicon metabolism into shells of two diatom species (Cyclotella cryptica and Nitzschia spec.) and reisolated by dissolving the shells. Contaminating isotopes 3H and 60Co with 10000 times more activity were largely removed by this procedure.

Facultatively anaerobic nitrogen-fixing bacteria from the marine environment

Anaerobic nitrogen fixation in the dark was determined in a natural marine community, developed in a laboratory model ecosystem, at the Oregon State University Marine Science Center in Newport, Oregon. Fixation occurred at a rate of 10 nmol C2H4/cm2 per 24 hours. Two different marine N2-fixing bacteria were isolated from seawater and from sediment at the Oregon coast. These bacterial isolates were identified as Klebsiella pneumoniae and Enterobacter aerogenes. Within a growth period of 100 h K. pneumoniae fixed 3.6 mmol N2 per liter and E. aerogenes fixed 1.2 mmol N2 per liter. The influence of seawater on N2-fixation activity of these bacteria was compared with that of bacteria from a non-marine origin. The nitrogenase activity of a crude cell-free extract of E. aerogenes was dependent upon ATP and Na2S2O4 and proceeded at a rate of 3.9 nmol C2H4 per minute per milligram protein.