Poly biological role

Short segments of poly(dG—dC) incorporated within plasmids, or citcular DNA, adopt the Z-conformation under negative superhehcal stress. This left-handed DNA may be important in genetic control. On the other hand, the stmctural alteration of the helix requited in a B-to-Z transition within a plasmid is radical, and would involve either a multistep mechanism or the complete melting and reformation of helix. The improbability of such transitions has led to questions concerning the feasibility of a biological role for Z-DNA. 

Much of the current interest in poly terpenoids is concerned with their biological role. The C55 prenol (68 n = 3, m = 8) from Staphylococcus aureus was shown ... 

NAD+ does not only play a biological role as a coenzyme in oxidoreductases but also as a substrate with its nicotinamide moiety acting as a leaving group in enzymes, as poly(ADP-ribose) polymerase and sirtuins (23). This leads to an amplification of potential enzyme targets, well beyond oxidoreductases, and, thus, to a potential more general application of NAD(P)+ chemogenomics. 

Thus, any model designed to explain the biological role of poly(ADPR) has to consider that both structural constituents like histone H2B as well as DNA-binding enzymes like topoisomerase I and poly(ADPR) synthase are modified by poly(ADPR). Assuming that poly(ADPR) synthase remains attached to the chromatin when activated by a DNA break, I favor the idea that poly(ADP-ribosyl)ation of the isolated acceptors is primarily a function of their accessibility to the synthase. The acceptor proteins may merely function as matrix to permit the accumulation of relatively large amounts of poly(ADPR) at distinct sites of the chromatin adjacent to the stimulating event. Thus, poly(ADPR), probably in the form of a three-dimensional network, may represent a specific tool to introduce changes into the chromatin structure. 

Eukaryotic poly(A) polymerases have been the subjea of intensive studies on the mechanism and biological roles of polyadenylation. 

In biological systems, a macromolecular chain effectively selects a complementary one to form an intermacromolecular complex. In this way, very specific functionalities become effective. Synthetic polymers can also form intermacromolecular complexes, but the ability of a synthetic polymer to select only one objective polymer as in biological systems has not yet been realized, except for several specific systems of pairs of polymers which include one of the complementary base pairs of nucleic add individually, e.g. po y(A)-poly(U) and poly(I)-poly(C) (see Sect. 3.3). The intermacromolecular complex formation of synthetic polymers is controlled by many factors such as interaction forces, solvent, ionic strength, temperature, pH, etc. Moreover, the cooperative and concerted interactions of each active site play an important role in complex formation. These phenomena suggest that the selective intermacromolecular complexation can be realized under suitable conditions. 

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