Diguanosine nucleotides of fungi that regulate RNA polymerases isolated and partially characterised.

Three unusual phosphorylated diguanosine compounds called ‘hot spots’ HS-1, HS-2 and HS-3 (ref. LéJohn, H.B. Proc. Can. Fed. Biol. Soc. 18, 159, 1975) have been isolated as acid-soluble materials from several fungi, $\text{Achlya, Blastocladiella emersonii, Aspergillus niger}$ and $\text{Rhizopus stolonifer}$ in their vegetative phase. The nucleotides were purified from acid extracts of $\text{Achlya}$ and $\text{Blastocladiella}$. The tentative structures of HS-3 and HS-2 determined are GppppG and GppppGp. HS-1 structure is still in doubt but it is related to HS-2. The structures were deduced from enzymatic digestion and UV analyses of the products, molar ratios of guanosine and phosphate, and chromatographic behaviour on PEI-cellulose. All three compounds accumulated in an inverse manner with rates of RNA synthesis and directly with rates of protein synthesis. The acid-soluble pools of the three compounds fluctuated during the life cycle of $\text{Achlya}$, and just prior to sporulation, were excreted into the medium. HS-2 was convertible to HS-3 by acid hydrolysis.     

Aldehyde content and cross-linking of type III collagen.

Three phosphorylated dinucleosides designated HS1, HS2, and HS3, isolated from the water-mould $\text{Achlya}$, were shown to significantly inhibit ribonucleotide reductase activity from $\text{Achlya}$. All three compounds decreased CDP reduction in fungal extracts by 50% at concentrations of 0.1mM. At the same concentration HS3 also inhibited partially purified CDP reductase from Chinese hamster ovary cells by at least 80% but showed only 10% inhibition with enzyme from $\text{E.}\text{coli}$. ADP reductase activity from $\text{Achlya}$ was inhibited 50% by both HS1 and HS3 at 0.1mM. HS2 however, showed no inhibitory effect on purine reduction. The levels of ribonucleotide reductase during the asexual growth cycle of $\text{Achlya}$ correlated with thymidine uptake into DNA and with the synthesis of HS compounds.     

Antigenic homology of eukaryotic RNA polymerases

Facilitated by an improved enzyme purification procedure, antisera to calf thymus DNA-dependent RNA polymerase II was prepared in hens. Using immunoprecipitation and inhibition of enzymatic activity the immunological properties of several eukaryotic RNA polymerases were examined. Purified calf thymus and rat liver polymerase II exhibited antigenic homology. The partially purified amphibian ($\text{Xenopus laevis}$) and protozoan ($\text{Tetrahymena pyriformis}$) polymerase II had reduced crossreactivities. Calf thymus polymerase I also shared antigenic homology with the form II enzymes.     

Genetical and biochemical evidence that a novel dinucleoside polyphosphate coordinates salvage and de novo nucleotide biosynthetic pathways in mammalian cells

Studies with ‘wild type’ Chinese hamster ovary cells and mutant derivatives defective in purine salvage and $\text{de novo}$ nucleotide biosynthesis pathways have brought to light the possibility that an unusual dinucleoside polyphosphate, HS-3 (see appendix) is a crucial regulator of these two pathways. Three antitumor drugs, methotrexate, 5-fluorouracil and azaserine as well as L-glutamine, purines and pyrimidines were used to define the loci of HS-3 metabolism. Wild type and salvage pathways mutants accumulated HS-3 in the absence of glutamine. $\text{De novo}$ pathways mutant accumulated HS-3 only when purine was absent. Depletion of HS-3 was induced in wild type and $\text{de novo}$ mutant cell lines by purine compounds. Salvage pathways mutants did not cause depletion of HS-3 when supplied with purines or pyrimidines, except 5-fluorouracil. Data indicate that HS-3 is probably synthesised when an early step in purine nucleotide synthesis is blocked and depleted when the salvage pathways are operative. HS-3 may be an important factor in certain diseases involving nucleotide metabolism.     

Studies on invitro DNA synthesis: II. Isolation of a protein which stimulates deoxynucleotide incorporation catalyzed by DNA polymerases of E.coli

Purified RNA polymerase, DNA polymerase III and unwinding protein of $\text{Escherichia}\text{coli}$ catalyze limited rifampicin sensitive fd or ØX 174 DNA-dependent DNA synthesis. A protein has been partially purified from $\text{E.}\text{coli}$ which stimulates rifampicin sensitive dXMP incorporation in this system 20 to 30 fold. This protein also stimulates DNA synthesis catalyzed by DNA polymerases I and II; the stimulation occurs in reactions primed with natural and synthetic DNAs as well as RNA-DNA hybrids. The protein is not a product of the known dna genes. In contrast to the above system of purified enzymes, rifampicin sensitive dXMP incorporation in crude extracts of $\text{E.}\text{coli}$ is specifically dependent on fd but not ØX 174 DNA. An additional factor has been isolated from extracts of $\text{E.}\text{coli}$ which restores specificity to the purified rifampicin sensitive system by preventing ØX 174 DNA from serving as a template.     

Evidence for two RNA polymerases in Arthrobacter, a morphogenetic bacterium

Two DNA-dependent RNA polymerases have been isolated from $\text{Arthrobacter crystallopoietes}$, a bacterium with a distinct morphological life cycle. The two enzymes are different with respect to chromatographic and electrophoretic behavior, divalent cation requirement, and template activity with different DNA species. One appears to be similar in its properties and structure to $\text{E. coli}$ polymerase, the other is different, but the nature of the difference is not yet clear. The possible relationship of the two enzymes in a regulatory role in the life cycle has yet to be investigated.     

Increased levels of rat hepatic nuclear free and engaged RNA polymerase activities during liver regeneration.

Rat liver nuclei, seventeen hours after partial hepatectomy, showed a two to three-fold increase in total RNA synthesis $\text{in vitro}$ over the sham operated controls. When tested with exogenous synthetic template, this was found to be mainly a reflection of increased levels of both the nuclear free and engaged RNA polymerase activities $\text{per se}$. It was also observed that there was a greater stimulation of the species of RNA polymerase that are α-amanitin resistant than sensitive (3.2 μg/ml). This observation was further confirmed by DEAE-Sephadex column chromatography of the solubilized nuclear free and engaged RNA polymerases and found RNA polymerase I and IIIa were the major species greatly stimulated during this period of liver regeneration. These data suggest not only that there exists a sensitive equilibrium between the nuclear free and engaged RNA polymerases; they also suggest the possibility that RNA polymerase itself may play a positive role in the regulation of gene expression.     

Purification and Characterization of DNA-dependent RNA Polymerases from Cauliflower Nuclei

DNA-dependent RNA polymerases were solubilized from nuclei of cauliflower inflorescences and purified by agarose A-1.5m, DEAE-cellulose, DEAE-Sephadex, and phosphocellulose chromatography and sucrose density gradient centrifugation. RNA polymerases I + III were separated from II by DEAE-cellulose chromatography. Subsequent chromatography on DEAE-Sephadex resolved RNA polymerase I from III. RNA polymerases I and II were further purified to high specific activity by phosphocellulose chromatography and sucrose density gradient centrifugation. RNA polymerase I was refractory to α-amanitin at 2 mg/ml. RNA polymerase II was 50% inhibited at 0.05 μg/ml, and RNA polymerase III was 50% inhibited at 1 to 2 mg/ml of α-amanitin. The enzymes were characterized with respect to divalent cation optima, ionic strength optima, and abilities to transcribe cauliflower, synthetic, and cauliflower mosaic virus DNA templates.     

Mutational alteration of Bacillus subtilis DNA polymerase 3 to hydroxyphenylazopyrimidine resistance: polymerase 3 is necessary for DNA replication

A spontaneous mutant of $\text{Bacillus}\text{subtilis}$ resistant to killing by two hydroxyphenylazopyrimidines has been isolated. The DNA polymerase III of this mutant is resistant to inhibition by these drugs. The K_i for 6-(p-hydroxyphenylazo)-uracil (HPUra) is 20 μM, about 40 times higher than the K_i of the wild-type enzyme. The mutant and wild-type polymerases behave similarly during purification, are sensitive to N-ethylmaleimide and to 0.1 M KCl, and have the same K_m for dGTP (0.5 μM). The HPUra inhibition of both enzymes is attenuated competitively by dGTP. We conclude that polymerase III is the target for hydroxyphenylazopyrimidines $\text{in}\text{vivo}$, and since the drugs specifically inhibit replicative DNA synthesis, polymerase III is necessary for DNA replication.     

Structural requirements of quassinoids for the inhibition of cell transformation

The effects of eleven quassinoids on Rous sarcoma virus induced cell transformation and on growth of normal cells were examined. At concentrations of 0.15-1 μg/ml they inhibited foci formation (76–99 %) without toxic effects on normal cells. The most active compounds also affected virus production by transformed cells. In intact normal and transformed cells, protein and DNA synthesis was equally affected after 3 hours of exposure to quassinoids of both cell types. RNA synthesis was not inhibited. This study has shown that the structural requirement of a C-15 ester in the quassinoids for antileukemic activity $\text{in vitro}$ and $\text{in vivo}$ is not essential for their antitransforming activity.     

A template independent, rifampicin sensitive poly (A).poly (U) synthesizing activity present in Bacillus subtilis.

A template independent poly (A)·poly (U) synthesizing activity has been isolated from $\text{Bacillus subtilis}$. This activity is eluted from a DNA-cellulose column along with DNA-dependent RNA polymerase. The column fractions which exhibit this activity contain RNA polymerase holoenzyme plus a polypeptide which is slightly larger than sigma factor; pure RNA polymerase holoenzyme did not synthesize poly (A)·poly (U). The activity was dependent on the presence of ATP, UTP, and Mn⁺⁺ (Mg⁺⁺ could not substitute), and was inhibited by rifampicin, streptolydigin, and Cibacron Blue. The incorporation of nucleotides was not linear with time, but appeared after a lag period. The results suggest that a modified form of DNA-dependent RNA polymerase analogous to $\text{Escherichia coli}$ holoenzyme II is catalyzing the synthesis of poly (A)·poly (U).     

Template specificities of the RNA dependent DNA polymerase of different murine C-type virus particles.

The crude RNA dependent DNA polymerase of seven different C-type viruses (AMV, Kirsten-MSV produced by NRK or $\text{NIH}\text{3T3}$ cells, Moloney-MuLV, Kirsten-MuLV, the murine myeloma associated virus (MuMAV) from FLOPC-1 and MOPC-21) was analyzed for their ability to utilize four different synthetic $\text{RNA}\text{DNA}$ hybrids or three different $\text{DNA}\text{DNA}$ duplexes as templates. The polymerases from AMV and murine sarcoma or leukemia viruses were distinctly different in their template stimulated activities and the two MuMAV polymerases were different from all of the other enzymes. MuMAV RDDPs were not stimulated by any of the synthetic $\text{RNA}\text{DNA}$ hybrid templates to the same level as the enzymes of the other C-type viruses and their ability to distinguish between templates was also different.     

Purification and Subunit Structure of DNA-dependent RNA Polymerase III from Wheat Germ

A rapid and simple, large-scale method for the purification of DNA-dependent RNA polymerase III (EC 2.7.7.6) from wheat germ is presented. The method involves enzyme extraction at low ionic strength, polyethyleneimine fractionation, (NH₄)₂SO₄ precipitation, and chromatography on DEAE-Sepharose CL-6B, DEAE-cellulose, and heparin agarose. Milligram quantities of highly purified enzyme can be obtained from kilogram quantities of starting material in 2 to 3 days. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis indicates that RNA polymerase III contains 14 subunits with molecular weights of: 150,000; 130,000; 94,000; 55,000; 38,000; 30,000; 28,000; 25,000; 24,500; 20,500; 20,000; 19,500; 17,800; and 17,000. Subunit structure comparison of wheat germ RNA polymerases I, II, and III indicates that all three enzymes may contain common subunits with molecular weights 20,000, 17,800, and 17,000. In addition, RNA polymerases II and III may contain a common subunit with a molecular weight of 25,000, and RNA polymerases I and III may contain a common subunit with a molecular weight of 38,000.     

Tryptophan uptake by Mycobacterium tuberculosis H37Rv--inhibition by isoniazid.

The effect of various sub-inhibitory concentrations of isoniazid on tryptophan uptake by $\text{Mycobacterium tuberculosis}$ H₃₇Rv grown $\text{in vitro}$ and $\text{in vivo}$ was studied. Uptake, measured after 3 minutes of drug exposure was inhibited mildly by 0.1 μg/ml and 0.2 μg/ml concentration and completely by 0.3 μg/ml. However, with the minimal inhibitory concentration (MIC)⁷ of 0.5 μg/ml, not only inhibition but also a strong efflux of the preformed tryptophan pool were observed. The results are discussed in the light of the theory that isoniazid interferes with the cell wall mycolate synthesis.     

Synthesis and properties of a new fluorescent analog of ATP: Adenosine-5′-triphosphoro-γ-1-(5-sulfonic acid) napthylamidate

An analog of ATP has been synthesized which contains the fluorophore, 1-aminonapthalene-5-sulfonate attached via a γ-phosphoamidate bond. This analog is strongly fluorescent (quantum yield = 0.63) with an emission maximum at 460 nm; the excited state lifetime is 20 nsec. It is a substrate for DNA-dependent RNA polymerase of $\text{E. coli}$ and wheat germ RNA polymerase II. It is also a substrate for $\text{E. coli}$ valyl t-RNA synthetase, venom phosphodiesterase, and potato apyrase. Cleavage of the α-β phosphoryl bond as a result of RNA synthesis or by venom phosphodiesterase produces a 15 nm red shift in the fluorescence emission spectrum. This property should make this nucleotide useful for studies of the mechanisms of enzymatic reactions involving cleavage of the α-β phosphoryl bond.     

DNA-dependent RNA-polymerases from Artemia embryos. characterization of polymerases I and II from nauplius larvae.

Partial purification and characterization of DNA-dependent RNA-polymerases from nauplius larvae of the brine shrimp, Artemia salina, are described. Fractionation of solubilized RNA-polymerases on columns of DEAE-cellulose yielded partially purified preparations of RNA polymerases I and II. The properties of these enzymes were found to be similar to properties of corresponding enzymes from other animal sources. A significant change in the relative amounts of polymerases I and II occurs between 36 and 72 hr of development. Polymerase activity obtained from 36-hr nauplii consisted of approximately equal amounts of polymerases I and II, whereas polymerase II accounted for more than 80% of the activity recovered from 72-hr nauplii. Total polymerase activity was lower at 72 than at 36 hr. The significance of these changes in relation to the decrease in RNA synthesis in vivo that occurs after 36 hr is discussed.