Deoxyribonucleic acid looping

Closed circuit voltage, 3 410 Closed-circular DNA, 27 611. See also Deoxyribonucleic acid (DNA) Closed-closed tubular reactors, 25 288 Closed-loop bioremediation defined, 3 759t... 

Figure 7.5 Example of a chimeric oligonucleic acid and its modification. Chimeric RNA-DNA hybrids are used for correction of point mutations in target genes. One strand of this oligonucleic acid is composed of O-methyl-RNA (outline) with an interruption of 5 bases of deoxyribonucleic acid. X and Y are target residues for correction. In the complementary strand, there is a DNA nick, and T residues loop both ends. 3 -exonuclease and FEN-1 may act on the nick, PARP-1 possibly binds to and is activated by the nick, resulting in activation of damage response pathways. In the modified version, the 3 end is replaced by ribonucleic acids. The 5 end is extended, and the flipped back RNA tail is added. Thus, the nick is expected to be resistant to 3 -exonuclease and FEN-1. In addition, PARP-1 may not be activated by such a nick.

It is of interest to note that many natural forms of deoxyribonucleic acid (DNA) have been shown to be circular macromolecules [29]. Furthermore, a detailed knowledge of the properties and molecular conformations of cyclic polymers should lead to a better understanding of the behaviour of linear polymers, as well as giving new insights into the properties of rubbers, gels and other systems where closed loops are known to exist. 

The Helical Nature of Nucleic Acids. The double helix of nucleic acids has a diameter of 20 A. Dimensions such as these can be made visible in modern electron microscopes. In the photograph of a deoxyribonucleic acid preparation of bacteriophages (Fig. 28), even the twisted structure of the DNA can be distinguished. The entire, multiply looped thread is 500,000 A (= 50 /u) long, which corresponds to a molecular weight of 130 million. 

---