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PubMed1980

Purine base composition analysis of normal and tumor rat DNA.

Chemical and viral induced rat tumors were analyzed for their purine base composition and compared to normal tissue DNA'S. The tumors were induced by 7,12-dimethylbenz[a]anthracene (DMBA), 20-methylcholanthrene (MC), 3,4-benzopyrene (BP), 1,2-dimethylhydrazine (DMH) and Rous sarcoma virus (RSV). Normal DNAs were extracted from colon, caecum, liver, spleen and embryo and used as reference standards for base composition of normal rat DNA. The composition of purines was obtained by spectrophotometric estimation of the total adenine and guanine (A/G) contents after depurination of the DNA with 66% formic acid at 30 degrees C for 18 h and passage over a cationic exchange resin. Statistical comparison of the A/G molar ratios in normal rat DNAs (1.271) to those of chemical-induced primary tumors (1.342) has shown a highly significant increase. No significant differences could be detected when the base composition of the normals were compared to transplanted tumors, whether chemically or virally induced. Possible explanations from a mutational point of view are discussed.

Animals↗
PubMedDate not supplied

Placement and replacement of resin-based composite restorations in Italy.

The use of resin-based composite restorations, the reasons for failure, and the longevity of these restorations have been surveyed in 62 Italian private practices. Almost two-thirds of the 1025 restorations inserted were class 3 and 5 restorations, while 18% were class 1 and 2 restorations. Secondary caries was the most common reason reported for replacement of resin-based composite restorations (44%), followed by discoloration (21%), and bulk and margin fracture (14%). The age of restorations needing replacement was reported for 53% of the sample. The median longevity in this sample was calculated to be 3.3 years.

Composite Resins↗
PubMed1976

Base composition studies on mitochondrial 4 S RNA from rat liver and Morris hepatomas 5123D and 7777.

The major and modified base composition of mitochondrial 4 S RNA from rat liver and from Morris hepatomas 5123D and 7777 has been determined for 16 constituents using a chemical tritium-derivative method. The base composition of these mitochondrial 4 S RNA preparations was compared with the base composition of cytoplasmic and bacterial (Escherichia coli B and Bacillus subtilis) 4-S RNAs. The results of these studies are: 1. When compared with cytoplasmic 4 S RNA, the liver and hepatoma mitochondrial 4-S RNAs are characterized by high (A + U)/(G + C) ratios and low overall degrees of base methylation and modification. 2. The mammalian mitochondrial 4-S RNAs are qualitatively even more different from the bacterial 4-S RNAs than from their cytoplasmic counterparts. Thus, several modified constituents found in both cytoplasmic and mitochondrial 4 S RNA are absent from the bacterial 4-S RNAs. 3. Mitochondrial 4S RNA from both hepatomas was found to be under-methylated and undermodified when compared with normal liver mitochondrial 4S RNA. This trend is more pronounced for the rapidly growing hepatoma 7777 (i.e., 17% undermethylation) than for the more slowly growing hepatoma 5123D (i.e., 8% undermethylation). These findings are discussed in relationship to (1) results of other authors on composition of mitochondrial 4 S RNA, (2) special features of structure and biosynthesis of mitochondrial 4 S RNA, (3) the possible evolutionary origin of mitochondria and (4) the possible role played by aberrant mitochondrial 4 S RNA in altered mitochondrial protein synthesis in tumors.

Animals↗
PubMed1985

Spectrofluorometric determination of bacterial DNA base composition.

A spectrofluorometric technique for bacterial DNA base composition has been developed. This fast and simple technique requires two fluorescent dyes and a few inexpensive reagents. The data from this assay indicate that the guanine-cytosine content obtained was within acceptable statistical limits in comparison to commonly cited literature values. The spectrofluorometric technique is reliable and reproducible.

Base Composition↗
PubMed1969

The DNA base composition of individual chromosomes and chromosome segments from Chironomus tentans.

The base composition of DNA was determined for individual chromosomes from the dipteran Chironomus tentans and for each one of six different segments of one of the chromosomes. The isolations were carried out by micromanipulation and the DNA purines were first extracted from the isolated components and afterwards separated by means of microelectrophoresis on a cellulose fiber. It was found that DNA from this material has an unusual composition corresponding to a guanine + cytosine content of about 30%. This composition was not a function of the polytenic condition but was also found for DNA from testis tissue. Furthermore Drosophila has a more traditional base composition for the bulk of DNA. Statistically significant variations in base data were found between whole chromosomes as well as between the segments from one of the chromosomes.

Adenine↗
PubMed1973

Size and base composition of RNA in supercoiled plasmid DNA.

The average size and base composition of the covalently integrated RNA segment in supercoiled ColE(1) DNA synthesized in Escherichia coli in the presence of chloramphenicol (CM-ColE(1) DNA) have been determined by two independent methods. The two approaches yielded similar results, indicating that the RNA segment in CM-ColE(1) DNA contains GMP at the 5' end and comprises on the average 25 to 26 ribonucleotides with a base composition of 10-11 G, 3 A, 5-6 C, and 6-7 U.

Adenosine Monophosphate↗
PubMed1986

Differences in the long chain (sphingoid) base composition of sphingomyelin from rats bearing Morris hepatoma 7777.

The long chain bases of sphingomyelin from Morris hepatoma 7777 and host and control livers were analyzed by capillary gas liquid chromatography. Sphingosine (18:1) was the major long chain base of control livers (66.5%) and hepatomas (65.6%), but hepatomas also had a high percentage (9.3 vs 4.4) of the 16:1 homolog. Host liver had the most unusual long chain base composition, with ca. equal 16:1 (24.4%) and 18:1 (21.4%) and high amounts of 20-carbon bases (9.2% 20:0 and 15.3% 20:1). These differences may be related to the aberrant fatty acid metabolism known to occur in tumor-bearing animals. Such large perturbations in the long chain base composition of hepatic sphingomyelin are unprecedented and could have a major impact on the properties of host membranes.

Animals↗
PubMed1969

Deoxyribonucleic acid base composition in yeasts.

The deoxyribonucleic acid base composition of 15 species of yeasts was determined to obtain further clues to or supporting evidence for their taxonomic position. Species examined belonged to the genera Saccharomyces, Debaryomyces, Lodderomyces, Metschnikowia, and Candida. The range of moles per cent guanine plus cytosine (GC content) for all yeasts examined extended from 34.9 to 48.3%. The sporogenous species and the asporogenous yeasts spanned the range with 36.6 to 48.3% GC and 34.9 to 48% GC, respectively. Three Saccharomyces species (S. rosei and related species) exhibited significantly higher GC contents than S. cerevisiae, whereas the fermentative species D. globosus revealed a%GC more aligned to the S. rosei group than to the nonfermentative D. hansenii. Similar GC contents were demonstrated by L. elongasporus and its proposed imperfect form C. parapsilosis. The range of GC contents of various strains of three Metschnikowia species studied was 6.1%, with the type strain of M. pulcherrima having the highest GC content (48.3%) of all of the yeasts examined.

Candida↗
PubMed1978

Base composition studies on transfer RNA from normal and regenerating rat liver.

The base composition of bulk tRNA isolated from regenerating rat liver, 12, 18, 24 and 30 h after partial hepatectomy, was determined by a 3H derivative method. Only a few minor statistically significant changes (2--11%), as compared to sham-operated liver, were found at 18, 24 and 30 h after hepatectomy. These included a reduction in the amounts of adenosine and 3-(3-amino-3-carboxypropyl)-uridine, and an increase in the amounts of 1-methyl-adenosine, 1-methylguanosine, 3-methylcytidine and pseudouridine. Similarly, when the base composition of tRNA fractions from control and 24-h regenerating rat liver, partially purified by one-dimensional polyacrylamide gel electrophoresis, was determined, no gross differences were observed. These results suggest that the process of liver regeneration is not accompanied by a gross alteration of the modification pattern of tRNA.

Animals↗
PubMed1975

Effect of DNA base composition on the intercalation of proflavine. A kinetic study.

The effect of DNA base composition on the kinetics of the association between DNA and proflavine has been investigated using the temperature jump relaxation method. It is found that, regardless of the G + C base composition the results fit a two step mechanism, the second of which exhibits characteristics of intercalation of proflavine into DNA. However, they two equilibrium constants corresponding to these steps, KI and KII, depend on the nature of the DNAs. The constant KI is found to be an order of magnitude greater for M. lysodeikticus DNA (72% G + C) than for calf thymus DNA (48% G + C). Increasing G-C content thus appears to favor the intermediate non-intercalated complex of proflavine with DNA. Methylation of M. lysodeikticus DNA with dimethyl sulfate, preferentially yielding N7 methyl guanine as the modified base, again leads to an apparent two step mechanism, with the value of KI unchanged with respect to untreated DNA, while the affinity of proflavine for the intercalated complex measured by the value of KII increases for methylated DNA.

Acridines↗
PubMed1989

Spectrofluorometry of dyes with DNAs of different base composition and conformation.

The increase in fluorescence, upon interaction with several fluorescent dyes was found to depend on the base composition of DNA. 4',6-Diamidino-2-phenylindole-2 HCl and Hoechst 33258 which bind to AT base pairs show a logarithmic relation. This relation is linear when DNAs interact with mithramycin, chromomycin A3, and olivomycin, which bind to GC base pairs. Deviations from these relationships were observed for T2 DNA, containing hydroxymethylcytosine, and for 2C DNA, containing hydroxymethyluracil. On the basis of these data, a simple technique is proposed for determination of base composition. The presence of abnormal bases can be monitored by the use of given fluorophores. Fluorescence intensities were not modified upon linearization of covalently closed circular plasmid pBR322. Denaturation of lambda DNA was accompanied by a decrease of fluorescence, when complexed with the five dyes tested.

Base Sequence↗
PubMed1978

Ribosomal genes in Physarum polycephalum: transcribed and non-transcribed sequences have similar base compositions.

The transcribed and non-transcribed sequences in Physarum polycephalum ribosomal DNA (rDNA) were separated by restriction nuclease digestion of pure rDNA and the products fractionated by zone sedimentation in sucrose gradients. The base compositions of the fragments were determined by analytical centrifugation in CsCl or in CsCl with netropsin. All the fragments had dA + dT contents in the range 44-48%. From the known sequence arrangement and transcription pattern of Physarum rDNA it was concluded that coding sequences, transcribed but non-coding sequences, and non-transcribed sequences all possess similar base compositions, contrary to the situation in many other systems. The thermal denaturation profile of Physarum rDNA is reported. It suggests the rDNA sequence is complex and supports the above conclusion of limited heterogeneity of base composition.

DNA↗
PubMed1987

Circular dichroism of sanguinarine-DNA complexes: effect of base composition, pH and ionic strength.

The interaction of sanguinarine with various naturally occurring and synthetic deoxyribonucleic acids of different base composition and sequence has been studied from the measurement of circular dichroism spectroscopy in buffer of various ionic strengths and pH values where physico-chemical properties of DNA remain unchanged. Binding of sanguinarine to DNA causes a change in the circular dichroism spectrum of DNA itself by showing the increase of both positive and negative bands and appearance of a broad positive band with peak at 340 nm. All systems studied exhibit extrinsic positive band that is independent of DNA base composition and sequence. Calf thymus DNA-sanguinarine complexes in different salt concentrations show that, at saturation, the magnitude of molar ellipticity at 340 nm increases with decreasing sodium ions concentration. Sanguinarine-DNA complexes in buffer of various pH values also show that the molar ellipticity at 340 nm is greater in acidic pH and lower in alkaline pH. It is concluded that the alterations of secondary structure of DNA upon binding of sanguinarine is maximum in buffer of low ionic strength and acidic pH and the number of bound alkaloid molecules per base pair, at saturation, is more in G-C rich DNA than in A-T rich DNA.

Alkaloids↗
PubMed1984

The relationship between base composition and codon usage in bacterial genes and its use for the simple and reliable identification of protein-coding sequences.

Bacterial genes that code for proteins appear to possess a codon usage characteristic of their overall base composition. This results in different but predictable non-random distributions of nucleotides within codons, permitting the recognition of protein-coding sequences in a wide range of bacterial species. The nature of this distribution depends on the base composition of the coding sequence. The position-specific differences are especially conspicuous in genes of extreme G + C content, allowing the particularly reliable prediction of the reading frame and coding strand of experimentally determined DNA sequences. This finding has been exploited to identify the coding sequence of the viomycin phosphotransferase (vph) gene of Streptomyces vinaceus. An easily applied computer program ("Frame") has been written to carry out and display such analyses.

Bacterial Proteins↗
PubMed1978

Spectral analysis of high resolution direct-derivative melting curves of DNA for instantaneous and total base composition.

Derivative melting profiles of DNA have been obtained directly by recording the difference in absorbance between two identical solutions maintained at a small constant temperature differential. This deltaA is monitored continuously with increasing temperature in a ratio recording spectrophotometer. Resolution of complex hyperfine structure in the profiles of small homogeneous viral DNAs appears to be significantly better than has been produced by various numerical methods of differentiation. In addition, a spectral method has been modified that permits easy analysis for DNA base composition from the ratio of derivative melting curves obtained at 282 and 260 nm. Eight bacterial and three vertebrate DNAs have been analyzed for total base composition from the product of the instantaneous base composition at small temperature intervals (0.05 degrees C) throughout the entire melting region and the integrated area of the 282 nm profile. The results are in excellent agreement with values determined by traditional methods.

Bacillus subtilis↗
PubMed1984

Deoxyribonucleic acid base composition and taxonomy of Moniliella and allied genera.

DNA base compositions of representative (type) strains of Moniliella, Trichosporonoides and Hyalodendron were determined. Within Trichosporonoides over 16% variance was found. Most species separated well, but M. suaveolens showed considerable heterogeneity. The standard 2% G + C differences for species distinction is probably not applicable to these yeasts. The new combination M. pollinis is proposed for M. tomentosa var. pollinis on the basis of slight ecological, morphological and physiological differences, supported by a marked difference in % G + C.

Base Composition↗
PubMed1990

DNA base composition determines the specificity of UvrABC endonuclease incision of a psoralen cross-link.

The sequences flanking a psoralen interstrand cross-link may determine how it is repaired. Our comparison of the Escherichia coli UvrABC endonuclease incision of a variety of specific cross-link sequences in a single natural DNA fragment showed that DNA base composition determines which of two cross-linked DNA strands will be incised. G/C enrichment of the region 6-12 bases 5' of the modified T on the furan-side strand results in preferential incision of the furan-side strand. When the G/C-rich region is on the 3' side, or on neither side, incisions occur on either strand. These effects of DNA base composition suggest that UvrAB can bind in two ways to a psoralen cross-link.

Base Composition↗
PubMed1973

Variation of type-B DNA x-ray fiber diagrams with base composition.

Eight natural DNAs of widely differing base composition have been studied by x-ray diffraction in fibers at high relative humidity. The resulting type B diffraction diagrams showed that all of the DNAs had a 34-A pitch and 3.4-A interbase pair separation. However, the intensity distribution on the inner three layer lines was a strong function of the base content. In diffraction diagrams of very AT-rich DNA, the intensity of the first and third layer line was 2- or 3-times stronger than in the patterns of GC-rich DNA. These high humidity diffraction patterns agree with x-ray scattering from solutions of DNA. The results are interpreted to imply that each AT base pair may have a different cross section than a GC pair. If this is so, it would appreciably alter the currently held ideas concerning DNA recognition.

Animals↗