PubMed Health⌕ Search

Biomedical subjects

A T Ansevin

Publications and source records attributed to A T Ansevin.

At least 19 recordsLinked to original sources
PubMed1990

Evidence for a new Z-type left-handed DNA helix: properties of Z(WC)-DNA.

The structure of Z-DNA, currently accepted as a model for all left-handed DNAs, fails to provide convincing explanations for at least four well established properties of left-handed DNA polymers in solution. However, the major discrepancies between theory and experiment are resolved by the structure presently proposed for Z[WC]-DNA, a new left-handed, zig-zag double helix with Watson-Crick-type backbone directions. Structural features of Z[WC]-DNA include the presence of an additional H-bond between each guanine N2-amino group and an adjacent phosphate oxygen, the capacity to form four-stranded, base-matched complexes that should readily precipitate from solution, and backbone progressions that are the same as B-DNA (opposite to Z-DNA). However, since Z[WC]-DNA and Z-DNA have many parameters in common, they could be difficult to distinguish in a majority of existing experiments. In view of the close relationship of the new helix to B-DNA, which allows a relatively unhindered right-to-left transition in handedness, Z[WC]-DNA is theorized to be the left-handed structure preferentially generated in vivo by the torque available in naturally occurring DNA supercoils.

Base Composition↗
PubMed1989

Specific translocation of tuftsin (Thr-Lys-Pro-Arg), a natural immunomodulating peptide, into the nuclei of human monocytes.

To delineate the mechanism of growth and differentiation activities of tuftsin (Thr-Lys-Pro-Arg), we examined the translocation of tuftsin after internalization by the target cells. We found using two independent techniques, fluorescence microscopy and autoradiography, that while in human polymorphonuclear leukocytes (terminally differentiated cells) the peptide remains in the cytoplasmic compartment, in monocytes it translocates to the nucleus. The ability of tuftsin to directly interact with DNA was documented by a large increase in the melting point of bovine DNA in the presence of tuftsin. It is suggested that the translocation, processing and action of tuftsin may depend on the differentiation state and/or on the type of effector cells. Also, tuftsin has the capacity to interact directly with DNA and, therefore, may have a potential for affecting gene activity.

Autoradiography↗
PubMed1984

An analysis of repeated sequence heterogeneity.

High-resolution thermal denaturation was used to measure the heterogeneity within repeated DNA sequences. An analysis of combined denaturation/redenaturation experiments on mouse satellite DNA suggests the existence of two minor components, one of which does not appear in the prepared EcoRII monomer. The resolving power of the denaturation/redenaturation experiment is estimated and contrasted with that of the reassociation experiment, often used to estimate repeated sequence heterogeneity. A mathematical model of the redenaturation experiment was developed and applied to mouse satellite data; the results suggest that only one-fourth of the mismatched base pairs are energetically significant in the reduction of heteroduplex stability.

Animals↗
PubMed1984

Dual-mode computer processing for high resolution DNA thermal denaturation experiments.

Two modes of data processing are appropriate in conducting high resolution thermal denaturation experiments (thermal increments of 0.05 degrees or closer). In the first mode, a general purpose microcomputer provides on-line services important to the control and monitoring of the initial experiment, including control of the spectrophotometer and heater, the recording of data, and the display of current hyperchromicities and approximate first derivatives. A subsequent microcomputer program then reads the recorded data files and carries out accurate calculations of derivative denaturation profiles and the estimate of the statistical error of the first derivative at each point. The data collection program handles three samples at a time and was designed to provide optimal results in thermal denaturation experiments with a single-beam spectrophotometer.

Computers↗
PubMed1983

Similarity of genetic distance determined from DNA thermal denaturation profiles to standard estimates of bacteriophage relatedness.

High resolution thermal denaturation profiles of a series of potentially related bacteriophages of Bacillus subtilis contain a multitude of distinctive features that permit them to be divided into at least four groups. In addition, the profiles can be used to derive the quantitative parameter, genetic distance, defined by Soumpasis (Soumpasis, D. (1980) J. Theor. Biol. 86, 137-147). Both the quantitative and the qualitative intercomparisons of profiles are in general agreement with the results of standard techniques for estimating genetic relatedness.

Bacillus subtilis↗
PubMed1978

Saltatory thermal denaturation of double-stranded viral RNAs.

The double-stranded RNAs from bacteriophage phi6 and the replicative form of mengovirus denature upon heating in a series of abrupt steps which resemble the subtransitions (thermalites) observed within the high resolution profiles of small, naturally occurring DNA molecules. Such RNA thermalites are approximately an order of magnitude narrower than typical thermal subtransitions of nominally single-stranded RNA. We conclude that the same features of nucleotide sequence that give rise to cooperative denaturation in DNA genomes are to be found also in RNA genomes. Thus, high resolution thermal denaturation profiles are useful for characterizing double-stranded RNA molecules as well as native DNA in the size range of common viruses. A medium containing dimethylsulfoxide was required to lower the Tm of the RNA samples to a satisfactory temperature range. For double-stranded RNA in 50% dimethylsulfoxide, the dependence of Tm on G . C composition was greater than that of DNA in the same medium and also greater than that of double-stranded RNA in an aqueous medium. The fact that RNA thermalites are broader than DNA thermalites and that the melting temperature of double-stranded RNA has a greater dependence on base composition than that of DNA, indicates that at least one of the thermodynamic parameters for double helix formation in RNA is different from that in DNA.

Bacteriophages↗
PubMed1976

High resolution thermal denaturation of DNA: thermalites of bacteriophage DNA.

High resolution thermal denaturation profiles are presented for the DNAs of bacteriophages lambda and T7. It is concluded that the temperature increment in data gathering and the method of calculating results meet the requirements for quantitative recording of the large amount of information found in the thermal transitions of both DNAs. The high resolution derivative denaturation profiles of these bacteriophage DNAs demonstrate that individual subtransitions (thermalites) of natural DNA are Gaussian in form and have narrow transition widths. Curve resolution performed on these profiles indicates that the mean thermalite width (2 sigma) is 0.33 degrees C and that this breadth is relatively invariant. Transition widths are not influenced by the position of thermalites in the profile or by cation concentration in the range from 5 to 30 mM Na+. However, the relative position of thermalites within a denaturation profile is a function of the solution ionic strength. The distribution of lengths of the DNA sequences which these thermalites represent is broad, with a number average length of 900 base pairs. Although we find an approximate similarity between the number of thermalites in the denaturation profile of T7 DNA and the number of looping regions in the electron microscopic partial denaturation map of Gomez and Lang ((1972), J. Mol. Biol. 70, 239-251) we conclude that free solution thermal denaturation experiments can be compared only superficially to the mapping results.

Coliphages↗
PubMed1975

Association of tissue-specific histones with deoxyribonucleic acid. Thermal denaturation of native, partially dehistonized, and reconstituted chromatins.

First derivative thermal denaturation profiles were compared for chromatin samples prepared from chicken erythrocytes, chicken liver, and sea urchin (Strongylocentrotus purpuratus) sperm. Selective dissociation of various histone fractions, including tissue-specific F2c and gamma histones, was manifested in characteristic changes of the thermal denaturation profiles. It was concluded that the binding of individual histone fractions to the DNA can be identified with paricular temperatures of thermal denaturation. This observation was tested by denaturation experiments on hybrid chromatins. Chicken erythrocyte chromatin devoid of F2c histone and reconstituted with isolated liver F1 histone denatured like chicken liver chromatin. Conversely, chicken liver chromatin devoid of F1 histones and reconstituted with isolated F2c fraction exhibited a thermal denaturation profile characteristic of the chicken erythrocyte chromatin. In other words, the thermal denaturation profile of reconstituted chromatin was determined approximately by the sum of contribution histone fractions. The obvious distinctions recognized among the derivative thermal denaturation profiles of compositionally different nucleoproteins suggest that thermal denaturation sensitively detects variations in histone content and therefore is a valuable tool for the routine characterization of chromatin preparations.

Animals↗
PubMed1975

Mechanics of chromatin template activation. Physical evidence for destabilization of nucleoproteins by polyanions.

Thermal denaturation profiles were used to quantitate the destabilizing activity of five classes of polyanions in an effort to explain previously reported differences in activity among apparently similar polymers. This physical assay for polyanion action on chromatin is free of the biochemical complications associated with template assay systems. Most polyanions tested caused a thermal destabilization of the normal nucleohistone complexes of rat thymus chromatin and exposed free or weakly complexed DNA. Polyphosphates dissociated chromatin even when their net charge was as low as 6, and activity per unit of weight increased with chain length only for polymers containing less than about 20 phosphate units; pyrophosphate was inactive. Two polymers which had no influence on chromatin had a low negative charge density. Some, such as polycytidlate and denatured DNA, possessed a high charge but caused only minor changes in the shape of denaturation profiles and exposed little or no free DNA. The highly active nucleic acids, ribosomal RNA and polyguanylate, were distinguishable from inactive nucleic acids by having more secondary structure and potentially less steric hindrance for anionic interaction with chromatin. There was evidence that some polyanions dissociate certain histones before others. Although data obtained show that some histones may be redistributed from chromatin onto added double-stranded DNA in a medium containing urea, this does not appear to interfere significantly with the interpretation of typical thermal denaturation profiles of chromatin.

Animals↗