DNA, light

Fig. 18. Metaphase image of a mouse/human hybrid bearing multiple human chromosomes, probed with FITC-biotinylated human DNA (light gray) and counterstained with propidium iodide (dark gray). The human chromosomes show up in light gray as a result ofacombined signal of FITC and PI. (Sample courtesy of Dr. Roger A. Schultz, University of Maryland School of Medicine, Baltimore, MD.)...

The ability of the dinuclear Ru (tpphz) species (tpphz = tetrapyr-idophenazine) to play as DNA light-switch is quite well known. But only recently it has been demonstrated that the 2P-PLIM based imaging of DNA at lifetimes of more than 160 ns is made possible by these complexes, totally removing any possibility of crosstalk from endogenous fluorophores. ... 

Interactions with DNA Light-Switch Effect and Phototherapy... 

Fig. 86. Structure of nucleohistone shown as a section cut perpendicularly to the long axis of the particles. Darkly shaded circles denote DNA, lightly shaded circles regions containing histone, a) Isotropic solutions, structure of one multistranded particle 4 DNA molecules are located in the center of the micelle b, c) other types of possible structures (Luzzati and Nicolaieff, 1963).

Chemiluminescence has been studied extensively (2) for several reasons (/) chemiexcitation relates to fundamental molecular interactions and transformations and its study provides access to basic elements of reaction mechanisms and molecular properties (2) efficient chemiluminescence can provide an emergency or portable light source (J) chemiluminescence provides means to detect and measure trace elements and pollutants for environmental control, or clinically important substances (eg, metaboHtes, specific proteins, cancer markers, hormones, DNA) and (4) classification of the hioluminescent relationship between different organisms defines their biological relationship and pattern of evolution. 

Modified oligonucleotides can be used to cross-link DNA sequences via a reactive group tethered to an oligonucleotide. When irradiated with uv light, psoralens (31) reacts with thymine bases, and the reaction yields a cross-link if the thymine residues are adjacent to each other on opposite strands. Psoralen linked to oligonucleotides have been shown to induce site-specific cross-links in vitro (51). 

Figure 7.2 Three helical forms of DNA, each containing 22 nucleotide pairs, shown in both side and top views. The sugar-phosphate backbone is dark the paired nucleotide bases are light, (a) B-DNA, which is the most common form in cells, (b) A-DNA, which is obtained under dehydrated nonphysiological conditions. Notice the hole along the helical axis in this form, (c) Z-DNA, which can be formed by certain DNA sequences under special circumstances. (Courtesy of Richard Feldmann.)...

Certain strains of Escherichia coli can be stimulated by irradiation with a moderate dose of ultraviolet (UV) light to stop normal growth and start producing bacteriophages that eventually lyse the bacterium. Bacteria of these so-called lysogenic strains carry the DNA of the phage integrated into their own... 

Figure 9.13 The DNA-binding region of the protein Oct-1, the POU region (green), comprises two domains, the POU-specific domain (dark green) and the POU homeodomain (light green) joined by a linker region (blue). These two domains bind to DNA in a tandem arrangement.

By examining some of the over one thousand tumor-causing point mutations of p53 in the light of its structure, we can identify features of p53 that are necessary for tumor suppression. The amino acids most frequently changed in cancer cells are at or near the protein-DNA interface residues that are infrequently mutated, if at all, are in general far from the DNA-binding site. 

Avery s studies shed light on the function of DNA. Chargaff s touched on structure in that knowing the distribution of A, T, G, and C in DNA is analogous to knowing the fflnino acid composition of a protein, but not its sequence or three-dimensional shape. 

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