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PubMed1977

Platinum - dimethylsulphoxide as a specific nucleic acid reagent for base sequence determination by electron microscopy.

The reaction of platinum (II) - dimethylsulphoxide complex with the bases of the nucleic acids were investigated with a new towards their use as heavy atom markers for base sequence determination by electron microscopy. Both at pH 6.0 and pH 7.5 one platinum atom was bound simultaneously to the pyrimidines and two to adenine, while at the lower pH one platinum, and at the higher pH, two platinum atoms were bound to guanine. The stain therefore appears to be useful to determine the guanine and adenine sequence in single strands of RNA and DNA. Where complementary strands are available the complete sequence determination of all four bases should be possible.

Base Sequence↗
PubMed1977

The interaction of polyxanthylic acid with polyadenylic acid.

The stoichiometry of interaction between polyxanthylic acid (poly(X)) and polyadenylic acid (poly(A)) was investigated by construction of mixing curves as a function of wavelength. Wavelengths were found which exhibited a break at 48-50 mol % poly(A) or two breaks, one at 48-50 mol % poly(A) and the other at 33-30 mol % poly(A). The melting profile (in 0.1 M salt) of the 50 mol % poly(A) mixture was monophasic (Tm=83 degrees C) at all wavelengths but that of the 33 mol % poly(A) mixture was biphasic showing a transition at Tm=40 degrees C and another at Tm=83 degrees C. Construction of a mixing curve between poly(A) and poly(X) at a temperature of 52 degrees C gave rise to plots which showed only one break (at 49--50 mol % poly(A)) at all wavelengths. Thus, while (at 20 degrees C in 0.1 M salt, pH 7) both poly(A)-poly(X) and poly(A)-2 poly(X) form at their respective stoichiometric end-points, the triplex poly(A)-2 poly(X), upon melting undergoes a disproportionation reaction resulting in the loss of one poly(X) strand and the formation of the poly(A)-poly(X) duplex.

Binding Sites↗
PubMed1978

The complexing of guanine nucleosides by poly(inosinic acid).

Under conditions where it is single-stranded (pH 7.0, 0.05 M Na+), poly(inosinic acid) complexes guanosine and 2'-deoxyguanosine in a strongly cooperative process that ultimately results in gel formation. The binding isotherm for formation of the poly(I).deoxyguanosine complex at 3.5 degrees C shows that it contains approximately one molecule of deoxyguanosine bound per IMP residue of the poly(I). This is compatible with the complex having a structure similar to that of the four-stranded secondary structure of poly(I) in which two of the poly(I) strands are replaced by helical arrays of deoxyguanosine molecules. The complex is laevorotatory at wavelengths longer than 300 nm. Optical rotation and ultraviolet absorbance versus temperature profiles show that on thermal dissociation the complex undergoes a co-operative helix-coil transition with Tm in the range 10--20 degrees C.

Deoxyguanosine↗
PubMed1978

Influence of polyamines on the activity of DNA polymerase I from Escherichia coli.

The influence of polyamines on the various activities of DNA polymerase I from Escherichia coli (EC 2.7.7.7) has been investigated. For all high molecular weight DNAs spermine and spermidine caused up to 80% inhibition when present in high concentrations, i.e. above 1 mM for spermine and 2 mM for spermidine. In the presence of low concentrations of polyamines a small activation was seen for some DNAs. The diamines cadaverine and putrescine had little influence on the rate of synthesis with natural occurring DNAs. In the case of d(A--T)n the activation/inhibition was found to be markedly dependent on the molecular weight of the samples used. With a low molecular weight DNA, 5.6 S, addition of spermidine resulted in up to 3-fold stimulation of activity. The activation was dependent on the concentration of MgCl2 and ionic strength; increasing concentration of these gave a decrease in the degree of activation. Polyamines also had a dramatic effect on the rate of synthesis using the homopolymers (dA)n . (dT)10 and (rA)n . (dT)10 . (20:1) as primers. Putrescine, in particular, increased the activity up to 10-fold with (rA)n . (dT)10 and somewhat less for (dA)n . (dT)10. The apparent Km for the primer (rA)n . (dT)10 decreased approx. 35-fold in the presence of 6.6 mM putrescine. There was no influence on the apparent Km for dTTP. The influence of polyamines on both the 5' leads to 3' and 3' leads to 5' nuclease activity was also investigated. Inhibition of nuclease activity was observed in the presence of polyamines, particularly with spermine. Thus with d(A--T)n and T7 DNA as substrates addition of 0.7 mM spermine resulted in almost complete inhibition of the activity. The dramatic inhibition observed with high concentrations of spermine (spermidine) both in the case of polymerizing and nuclease activity is thought to be due to polyamine-induced aggregation of DNA molecules.

Cadaverine↗
PubMed1978

Electrostatic complexes of mitomycin C with nucleic acids and polyanions.

Reductively activated mitomycin C exhibits strong, non-covalent electrostatic binding to polyanions such as polyvinylsulfate and polyphosphate. The protonated C-2 amino group generated by the reduction is most likely responsible for this type of interaction. At moderate drug and salt concentrations only covalent binding to nucleic acids is observable. This is shown to be guanine-specific in DNA for the first time, as well as in synthetic polyribo- and polydeoxyribonucleotides at 10--20 times higher binding levels than previously tested. At higher mitomycin C concentration, however, strong non-covalent electrostatic binding to nucleic acids also occurs, resulting in a binding ratio up to 1 mol drug bound per mol mononucleotide, although this non-specific binding is relatively inhibited compared to polyvinylsulfate. Salts also have an inhibitory effect on the non-specific binding to nucleic acids. A series of mitomycin derivatives were compared for their binding and cross-linking abilities using DNA as substrate, with the following results: (a) the presence of a basic nitrogen . funtion at C-2 promotes binding, both covalent and electrostatic, presumably by kinetically facilitating the approach between positively charged nitrogen and DNA. (b) The aziridine ring is the major covalent binding site, indispensable for crosslinking and determines the guanine-specificity of the binding.

Anions↗
PubMed1979

A method for the synthesis of oligonucleotide by single addition of 2'-O-(o-nitrobenzyl)nucleoside 5'-diphosphates using polynucleotide phosphorylase.

Two hexanucleotides A-U-G-U-G-A and C-A-A-U-U-G were synthesized from the chemically synthesized trimers C-A-A and A-U-G by addition of 2'-O-(o-nitrobenzyl)nucleoside diphosphates using polynucleotide phosphorylase isolated from either Escherichia coli or Micrococcus luteus. In each reaction the preference of the enzyme was tested. The o-nitrobenzyl group was removed after addition of the mononucleotide and the deblocked product was isolated by chromatography on DEAE-Sephadex in high yields.

Adenosine Diphosphate↗
PubMed1979

Polynucleotides XLVII. Synthesis and properties of poly(2-methylthio- and 2-ethylthioadenylic acid). Formation of non-Watson-Crick type complexes.

Poly(2-methyl- and 2-ethylthioadenylic acid) were prepared by polymerization of corresponding diphosphates with Escherichia coli polynucleotide phosphorylase. These polynucleotides have relatively large hypochromicity of 30-35%. Acid titration of these polymers showed abrupt transition at pH 5.34-5.4, which may indicate that the introduction of alkylthio group at 2-position of adenine bases reduced their basicity. Thermal melting of these polymers showed no clear transition points at neutral pH, but in acidic media they have Tm values of 57 and 56 degrees C, somewhat lower than that of poly(A). Upon complex formation with poly(U), these poly(A) analogs showed only one poly(rs2A) . poly(U) type double-strand complexes, similar to that found in the case of poly(m2A) . poly(U).

Circular Dichroism↗
PubMed1979

Physical and coding properties of poly(5-methoxyuridylic) acid.

The synthesis of poly(mo5U) requires a high concentration (2.7 mg/ml) of polynucleotide phosphorylase as well as a long reaction time (48 h). The resulting polynucleotide has a chain length of approximately 100 nucleotides. It shows no indication of a stable secondary structure. When poly(mo5U) is mixed with poly(A), a triple-stranded complex poly(A) . 2poly(mo5U) is formed. This complex has a melting temperature of 68.5 +/- 0.5 degrees C at 150 mMNa+ and exhibits a hysteresis loop between melting and reformation of the complex having a delta Tm of 11.5 degrees C. Poly-5-methoxyuridylic acid stimulates the binding of Phe-tRNA to 70-S ribosomes but is inactive in directing poly(Phe) synthesis.

Escherichia coli↗
PubMed1981

Polynucleotide synthetase of E. coli: an enzyme complex having polynucleotide phosphorylase as apoenzyme.

A previously described synthetase system of Escherichia coli that utilizes ribonucleoside triphosphates has been purified extensively and shown to consist of an apoenzyme and three protein factors. The apoenzyme itself was revealed to be polynucleotide phosphorylase. The conditions under which the latter - an enzyme incorporating nucleoside diphosphates - is converted to a system catalyzing the uptake of nucleoside triphosphates have been studied in detail with respect to primer requirements, the influence of triphosphates on diphosphate utilization and vice versa, and the possibly regulatory effect of the guanosine di- and triphosphates. The fully supplemented enzyme system (polynucleotide synthetase) incorporates GTP only in the presence of ATP, producing a polynucleotide with an A : G ratio near unity.

Apoenzymes↗
PubMed1981

Inhibition of the action of Escherichia coli transcription termination protein rho by poly(C) and heparin.

Poly(C) and heparin at low concentrations (1 microgram/ml) prevent the RNA synthesis termination protein rho from functioning during the biosynthesis of RNA from bacteriophage T7 DNA catalyzed by Escherichia coli RNA polymerase. Both of these polyanions inhibit the binding of rho to isolated T7 RNA. Heparin also inhibits rho ATPase when isolated RNA transcripts are used as cofactors. It is concluded that the polyanions inhibit termination by binding to the site on rho that is normally used for the initial interaction with a nascent RNA transcript in the rho-mediated release of RNA. Since one of the inhibitors, poly(C), is itself a potent activator for rho ATPase, it is also concluded that the ATP hydrolysis step that is required for rho termination has to be coupled to an action of rho on the RNA molecule to be released from the transcription complex.

Adenosine Triphosphatases↗
PubMed1981

Influence of inorganic cations and histone proteins on the terbium(III)-nucleic acid interaction.

We have studied the interaction of the fluorescent lanthanide, terbium(III) (Tb3+), with polynucleotides and linear and superhelical DNA, through employment of mono- and multivalent cations as competitive inhibitors. Increasingly effective competitive inhibiton of the Tb3+-nucleic acid interaction was achieved, for the most part, in the cation order monovalent less than divalent less than tetravalent. The divalent cation Cu2+ proved to be an exception to this trend, and was the strongest competitive inhibitor or all cations tested, exhibiting an affinity for Tb3+ binding sites over twice that of Tb3+ itself. Unexpectedly, a narrow range of low sodium ion concentration (8--20 mM) was found to be effective in inducing localized unwinding or unstacking of linear and supercoiled DNA double helices, a phenomenon detectable through the use of both Tb3+ fluorescence enhancement and ultraviolet spectroscopy. Within a similar range of low sodium ion concentration, moreover, histone H1 was substantially more effective in displacing terbium ion from DNA than either histones H2B or H4, but at higher ionic strength, this difference was absent. These results further confirm the sensitivity and specificity of Tb3+ as a conformational probe of nucleic acids.

Animals↗
PubMed1981

An RNA-dependent ATPase from Chlamydomonas reinhardII.

An RNA-dependent ATPase has been isolated from extracts of Chlamydomonas reinhardii. The enzyme catalyzes the hydrolysis of ATP, dATP, CTP and dCTP to the corresponding nucleoside diphosphate and Pi in the presence of Mg2+ or Mn2+ and an RNA cofactor. In 1 mM MgCl2 it displays the greatest activity with poly(A), poly(I) and poly(U); and somewhat lower activity with poly(C) and T7 RNA. Although the enzyme is active with single-stranded DNA, all the single-stranded RNAs tested were significantly more effective cofactors than any of the single or double-stranded DNAs tested. A comparison of this ATPase with other RNA-dependent ATPases indicates that is has more in common with the ATPase isolated from the nuclei of animal cells than with the RNA synthesis termination protein rho, the major RNA-dependent ATPase from Escherichia coli. Although chloroplasts of C. reinhardii are known to contain many bacterial-like gene expression components, the presence of an enzyme with close homology to the E. coli rho protein was not detected.

Adenosine Triphosphatases↗