DNA supercoiling

FIGURE 11.23 A diagram of the histone octamer. Nucleosomes consist of two turns of DNA supercoiled about a histone core octamer. 

Recent advances of the Seeman group led to the construction of a nanomechanical device from DNA [89]. In this molecular apparatus, the ion-dependent transition of B-DNA into the Z-conformation is used to alter the distance between two DNA DX domains attached to the switchable double helix. Atomic displacements of about 2-6 nm were attained. Ionic switching of nanoparticles by means of DNA supercoiling has also been reported [53]. Additional advances regarding the use of DNA is nanomechanical devices have been reported by Fritz et al., who showed that an array of cantilevers can be used to... 

The condensin complex has been identified in the same scaffold fraction (Maeshima and Laemmli, 2003) and shown to be essential for the mitotic chromosome condensation (Hirano et al, 1997). The frog condensin complex exhibits ATP-dependent DNA-supercoiling activity (Kimura and Hirano, 1997). It consists of a heterodimer of SMC and a trimer of non-SMC proteins (Hirano et al, 1997). The SMC complex has a globular head domain and a coiled-coil tail region (Anderson et al., 2002 Melby et al, 1998 Yoshimura et al., 2002). In vertebrates, two types of condensin complex, condensin I and condensin II, exist they are composed of the same SMC subunits but with different non-SMC subunits (Ono et al, 2003). 

Opel ML, Arfin SM, Hatfield GW (2001) The effects of DNA supercoiling on the expression of operons of the ilv regulon of Escherichia coli suggest a physiological rationale for divergently transcribed operons. Mol Microbiol 39 1109-1115... 

The idea that chromatin possessed some kind of repetitive particulate structure, rather than existing as a uniform, histone-coated DNA supercoil, emerged from a number of laboratories in the early 1970s (see Refs. [2-6]). At any event, by 1978, the basic concept of the nucleosomal core particle, as currently envisioned, was well established. The histone octamer, involving strong H3 H4 and H2A H2B... 

Duband-Goulet, I., Carol, V., Ulyanov, A.V., Douc-Rasy, S., and Prunell, A. (1992) Chromatin reconstitution on small DNA rings. IV. DNA supercoiling and nucleosome sequence preference. J. Mol. Biol. 224, 981-1001. 

Stros, M. and Muselikova, E. (2000) A role of basic residues and the putative intercalating phenylalanine of the HMGBl-box B in DNA supercoiling and binding to four-way DNA junctions. J. Biol. Chem. 275, 35699-35707. 

Crothers, D.M. (1993) Architectural elements in nucleoprotein structures. Curr. Biol. 3, 675-676. Stros, M. (2001) Two mutations of basic residues within the N-terminus of HMG-1 B domain with different effects on DNA supercoiling and binding to bent DNA. Biochemistry 40, 4769-4779. 

Chirico, G. and Langowski, J. (1994) Kinetics of DNA supercoiling studied by Brownian dynamics simulation. Biopolymers 34, 415-433. 

FIGURE 24-10 Supercoils. A typical phone cord is coiled like a DNA helix, and the coiled cord can itself coil in a supercoil. The illustration is especially appropriate because an examination of phone cords helped lead Jerome Vinograd and his colleagues to the insight that many properties of small circular DNAs can be explained by super-coiling. They first detected DNA supercoiling, in small circular viral DNAs, in 1965. 

DNA supercoiling is a precisely regulated process that influences many aspects of DNA metabolism. Every cell has enzymes with the sole function of underwinding and/or relaxing DNA. The enzymes that increase or decrease the extent of DNA underwinding are topoisomerases the property of DNA that they change is the linking number. These enzymes play an especially im-... 

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