Toroid DNA

Serum albumin Ferritin-like a /a toroid DNA/RNA-binding... 

Macromolecules capable of internal local orientational ordering, usually of nematic type, in the globular state, like in toroid DNA case. Macromolecules with other types of symmetry or organization in the globule, up to a crystal. 

Conwell, C.C., Vilfan, I.D., Hud, N.V. Controlling the size of nanoscale toroidal DNA condensates with static curvature and ionic strength. Proc. Natl. Acad. Sci. USA 100,... 

RNA and a TAR RNA dimer in the presence or absence of gold colloids have been described.Various nucleic nanostructures have been observed using AFM, including rectangular tiles, " cubes, circu-lari269,i27o toroidal DNA. The transition of B-DNA to Z-DNA in... 

The native form of chromatin in cells assumes a higher order stmcture called the 30-nm filament, which adopts a solenoidal stmcture where the 10-nm filament is arranged in a left-handed cod (Fig. 5). The negative supercoiling of the DNA is manifested by writhing the hehcal axis around the nucleosomes. Chromatin stmcture is an example of toroidal winding whereas eukaryotic chromosomes are linear, the chromatin stmctures, attached to a nuclear matrix, define separate closed-circular topological domains. 

Negatively supercoiled DNA can arrange into a toroidal state (Figure 12.26). The toroidal state of negatively supercoiled DNA is stabilized by wrapping around proteins which serve as spools for the DNA ribbon. This toroidal con-... 

FIG. 2 Atomic force microscopy of plasmid DNA at different stages of condensation with polycations. (a) Circular plasmid DNA (b) DNA condensed with poly-L-lysine (PLL, mol. wt. 4 kDa) at a DNA phosphate/lysine ratio of 2 1 (c) DNA condensed with PLL (mol. wt. 10 kDa) at a phos-phate/lysine ratio of 1 2 (d) toroid of DNA condensed with PLL-asialo-orosomucoid conjugate at a phosphate/lysine ratio of 1 6. [(a) and (d) from Ref. 80, copyright 1998 Oxford University Press (b) and (c) reprinted with permission from Ref. 66, copyright 1999 American Chemical Society.]... 

Figure 36-19. Supercoiling of DNA. A left-handed toroidal (solenoidal) supercoil, at left, will convert to a right-handed interwound supercoil, at right, when the cylindric core is removed. Such a transition is analogous to that which occurs when nucleosomes are disrupted by the high salt extraction of histones from chromatin.

Fig. 2. Model of a toroid-like complex between plasmid DNA and dendrimers. Dendrimer molecules (spheres) are located both inside and outside the coiled DNA molecules, and more than one plasmid DNA molecule can be present in one toroid-like complex. The left part of the graphic shows the most probable situation the dendrimers on the outside of the complex are not shown in the remainder of the graphic in order to give a better view of the inner part of the complex. The diameter of such a complex is approximately 50 to 100 nm...

Activated PAMAM dendrimers interact with DNA to form a DNA-dendrimer complex with a toroid-like structure (Fig. 2). Such DNA-dendrimer complexes have diameters of 50-100 nm [10],which means that the DNA molecules are highly condensed in these complexes. A 6-kb plasmid alone, for example, has an extended structure several hundred nanometers in diameter. In transfection experiments, typically an 8- to 12-fold excess of positive amino groups over negatively... 

The weakly immunogenic protamine sulfate USP (1) condenses DNA to form a toroid structure of super-coiled DNA about 50 nm in diameter (2). The DNA in this form or in the preformed LPDI complex cannot be displaced from the protamine by polycations such as spermidine and histones or by other nucleic acids like genomic DNA (2). DNA in this toroid structure is transcriptionally inactive and this conformation allows for protection of DNA from enzymatic degradation by nucleases and other environmental assaults such as mechanical stress (1,2). After the liposome surrounds the toroid, the resulting homogenous LPDI nanoparticles are slightly less than... 

Several AFM studies examined the effect of buffer conditions on the formation of motifs with DNA molecules. For instance, it has been foimd that the multivalent cations induce the condensation of DNA molecules into higher ordered structures, including toroids and rods [122], More specifically, Zn and Mg ions induce the formation of DNA kinked and perfect circles, respectively [123] (Fig. 16). Also, higher concentrations of spermidine induce the formation of complex flower-shaped structures with single crossover points [122] and increased concentrations of ethanol lead to complex and looped structures [ 124] (Fig. 17). 

Fig. 21 Image galleries of a toroidal and b rod-like DNA ensembles on chitosan surface [130]. Reprinted with permission...

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