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Biomedical subjects

E Hamori

Publications and source records attributed to E Hamori.

At least 19 recordsLinked to original sources
PubMed1989

HYLAS: program for generating H curves (abstract three-dimensional representations of long DNA sequences).

The computer program HYLAS generates from a standard DNA letter sequence a three-dimensional space curve (H curve) which embodies the entire information content of the original nucleotide sequence. The program can display H curves either as two-dimensional (front and side view) projections or as stereo-pair images. The curves can be marked at specific nucleotide locations, annotated, rotated for observation from any viewing angle, and manipulated for convenient side-by-side comparisons. Unlike the cumbersome letter sequences, H curves can be drastically condensed in size without losing their ability to reflect the global nucleotide-distribution pattern of the entire DNA sequence. Often, biologically important loci can be visually identified on the H curves. HYLAS is written in FORTRAN with separate mainframe (IBM-VM/CMS) and microcomputer (MS-DOS) versions. It uses the Tektronix-TCS library of graphic subroutines.

Base Sequence↗
PubMed1988

DNA sequence (H) curves of the human immunodeficiency virus 1 and some related viral genomes.

The complete nucleotide sequences of several human immunodeficiency virus 1 (HIV-1) genomes were converted by computer to respective H curves. These three-dimensional space curves embody all the information contained in the sequence due to their abstract vectorial structure. For one sequence (HIV-1 isolate BRU) special efforts were made to maximize the available resolution (the number of nucleotides visually discernible within a unit length of the curve) when making a hard, master copy of the H curve. Using a computergraphic/photographic hybrid process the 9191 nucleotides of this HIV-1 sequence were condensed into an H curve of only 37.1 cm vertical length. Although each 1-mm segment of this curve represented 25 nucleotide residues, each of the individual nucleotides of the entire sequence was still distinguishable upon direct inspection using a simple magnifying lens. Several functionally important loci of the HIV-1 sequence could be recognized on the H curve owing to characteristic line forms at corresponding locations. Utilizing H curves of lower resolution, the total nucleotide sequences of several different HIV-1 isolates and related viral sequences [Visna, equine infectious anemia (EIAV), Moloney murine leukemia (Mo-MLV), bovine leukemia (BLV), and human T-cell leukemia, type I (HTLV-I)] were visually compared side by side. An interesting similarity was noted between the location of the S3 fragment of the EIAV sequence and that of a relatively G-C rich region on the env portion of the HIV-1 sequences.

Base Sequence↗
PubMed1987

The B-Z conformational transition and aggregation of poly[d(G-C)] induced by moderate concentrations of Mg(CIO4)2.

Mg(ClO4)2 induces the cooperative B-to-Z transition of poly[d(G-C)]; the salt concentration at the midpoint is 0.26 M. A comparison with previous data for NaCl, MgCl2 and NaClO4 (F.M. Pohl and T.M. Jovin, J. Mol. Biol. 67 (1972) 375) indicates that Mg(ClO4)2 is more effective than would be anticipated from the simple additive effects of the Mg2+ and ClO4- ions (the ionic strengths of the respective transition points are: NaCl, 2.4; MgCl2, 2.1; NaClO4, 1.8 and Mg(ClO4)2, 0.78). These results suggest the importance of specific interactions involving ClO4-, particularly in the presence of Mg2+. The B-Z transition of poly[d(G-C)] can be monitored spectroscopically via the large hyperchromic shift at 295 nm and the inversion in the CD spectrum. The reaction is fully reversible and can be fitted by a monoexponential function with half times varying between 8 and 150 min. The observed relaxation times are strongly dependent on the concentration of Mg(ClO4)2 with a distinct maximum at the transition point, in accordance with a concerted mechanism involving only the B and Z states. As the polymer assumes the Z conformation it progressively aggregates into a gel-like precipitate, which, however, redissolves rapidly upon lowering the salt concentration. The natural DNA from Micrococcus lysodeikticus which has a high GC content of 72% is also precipitated by Mg(ClO4)2 but we do not have direct spectroscopic evidence for the involvement of the Z conformation in this phenomenon. Neither calf thymus DNA (41% GC) nor poly[d(A-T)] (0% GC) aggregates under the same conditions.

Chlorates↗
PubMed1983

H curves, a novel method of representation of nucleotide series especially suited for long DNA sequences.

In order to create an alternative to the customary letter-series representation of nucleotide sequences a novel method was developed based on computer graphics. In this new method, the information content of a nucleotide sequence is mapped into a three-dimensional space function (H curve) which can be displayed and manipulated conveniently. Even very long nucleotide sequences can be represented by compact H curves. Such curves are not only characteristic "fingerprints" of complex genetic messages but also embody important parameters concerning the distribution of nucleotides. H curves appear to be particularly suitable for the visual analysis and comprehension of both the local and the global features of long DNA sequences.

Base Sequence↗
PubMed1982

Study of unaided cross-eyed stereopsis.

The learning of the skill of unaided cross-eyed stereopsis was investigated on a group of young adults. Both pictorial and random-dot stereograms were used; small stereograms were viewed at normal reading distance and large projected stereograms were viewed in an auditorium. The results suggest that this direct stereoscopic technique can be learned within a few minutes by almost everyone in the population represented by the test group. The calculated eye-convergence angles for various conditions of cross-eyed stereoscopic viewing indicate that little eye discomfort is caused by this factor when the stereograms are located at a sufficient distance from the viewers. The comments of subjects support this conclusion. The unexpected prevalence of the aptitude for this skill should have practical application in the unaided three-dimensional visualization of computer-generated stereograms.

Accommodation, Ocular↗
PubMed1980

Selection of viable cells with known DNA content.

Cells doubly stained with Hoechst 33342 (H-33342) for DNA content and fluorescein diacetate for viability can be selected on the basis of both criteria using a single UV laser flow sorter. The selection is made possible due to resonance energy transfer occurring between the H-33342 and fluorescein fluorophores. Both a static fluorescence microscope and a dual laser flow sorter were used to demonstrate that energy transfer occurs in the doubly stained cells and that the sensitized emission in conjunction with the DNA emission can be used to select populations of cells with known DNA content and viability. The results indicate that fluorescein liberated by cellular esterases is freely accessible to the nucleus.

Animals↗
PubMed1975

Kinetic investigation of unfolding and partial refolding of a crab satellite (dA-dT)n.

Crab (dA-dT)n was isolated from the testes of Cancer borealis by a procedure involving separation of DNA and segregation of the satellite fraction by Hg2+ binding/Cs2SO4 density gradient ultracentrifugation. The titration of crab (dA-dT)n samples at 10 degrees indicated a sharp absorbance change at pH 11.98 in agreement with the pHm value observed for synthetic poly(dA-dT) under identical conditions. The reversal of the titration, however, resulted only in about 50% recovery of the original absorbance (at 260 nm) in marked contrast to the complete reversibility of the synthetic material. pH-jump experiments were carried out for the purpose of characterizing the rates and mechanisms of conformational transitions brought about by changes in the solution environment. It was found that the disintegration of the putative native structure of crab (dA-dT)n starts with a very fast reaction (occurring within the 6-msec deadtime of the instrument and comprising 65% of the total absorbance change) and it is completed via a slower first-order reaction (k = 66 sec minus 1). It is postulated that the first process is due to the rapid untwisting of end regions and, perhaps, some short hairpin-like helical branches present on the macromolecules. The second reaction is believed to be the end-to-end type unwinding of the double-helical backbone of crab (dA-dT)n. In the presence of low concentration (3 mug/ml) of Hg2+ ions the overall rate of disintegration process decreased drastically. pH jumps from pH values above pHm to values below were used to study the rates of absorbance changes corresponding to the refolding of the strands of denatured crab (DA-dT)n. A concentration independent process consisting of two phases was observed. The first phase was a gradual nonexponential process spanning the first second of the reaction, and the other, a very slow first-order process characterized by the rate constant value of 0.053 sec minus 1. It is proposed that the first part of the process (involving about 24% of nucleotide residues) is an intramolecular formation of helical hairpins (frequently interrupted by mismatching bases) and the second part is a manifestation of some association of the extant unpaired bases during the folding of the branched structure. Refolded crab (dA-dT)n samples when subjected again to pH greater than pHm in the stopped-flow apparatus displayed not the disintegration pattern of the native crab (dA-dT)n but rather that of synthetic poly(dA-dT. The marked facility of crab (dA-dT)n macromolecules for rapid conformational transitions induced by slight changes in the solution environment might be relevant to the biological function of this DNA.

Animals↗