Double stranded, conformation

Hilleman and his co-workers have demonstrated interferon production following the administration of reovirus RNA or the replicative form of RNA isolated from E. coli infected with MS2 coliphage. These BNAs are effective in inducing resistance to virus infection m vitro and vivo. The induction of interferon and the broad-spectrum protection against viral infection conferred by double-stranded RNA suggested the use of synthetic polynucleotides, including polyriboinosinic-polyribocytidilic acid, which possess a double-stranded conformation. Chemically modified RNA may also induce the production of interferon. ... 

The anti-poly I poly C antibodies react not only with RNA of reovirus but also, though to a lesser degree, with RNA extracted from mammalian cells (Fig. 4). Comparison of the efficiency of inhibition of the cross-reaction with mammahan RNA by RNA of reovirus, by double-helical complexes of synthetic polynucleotides and by single-stranded polynucleotides, has shown that the antibodies anti-poly I poly C react especially with double-stranded conformational determinants of the RNA. None of the single-stranded polynucleotides is capable of totally inhibiting the reaction with RNA whatever... 

We can conclude that the precipitation of the DNA-cationic surfactant systems does depend on whether the DN A is in the single- or double-stranded conformation. 

The conformational transitions in the presented model take place accord-itig to the all-or-nothing law, i.e. they occur at the certain r.h. value. The same behaviour has been observed, for example, for the helix-coil transition of the model double-stranded structure A(pA)i7-U(pU)i7 [24]. It is worth noting that this structure is homogeneous, the same is supposed in our model. 

The other important feature of the primary stmcture of RNA is the presence of the 2 -hydroxyl group in ribose. Although this hydroxyl group is never involved in phosphodiester linkages, it does impose restrictions on the heHcal conformations accessible to double-stranded RNA. 

The specific protein-DNA interactions described in this book are all with DNA in its regular B-form, or, in some cases with distorted B-DNA. In biological systems DNA appears not to adopt the A conformation, although double-stranded RNA does preferentially adopt this conformation in vivo. Whether or not Z-DNA occurs in nature is a matter of controversy. However, the formation of A-DNA and Z-DNA in vitro does illustrate the large structural changes that DNA can be forced to undergo. 

X-ray diffraction studies indicate the existence of a novel double-stranded DNA helical conformation in which AZ (the rise per base pair) = 0.32 nm and P (the pitch) = 3.36 nm. What are the other parameters of this novel helix (a) the number of base pairs per turn, (b) Abase pair), and (c) c (the true repeat) ... 

Identification of proteins that bind to Z-DNA added one further step to the establishment of the presence of Z-DNA in vivo and its possible biological role. Herbert and Rich [22] demonstrated an in vitro assay system where one type of double-stranded RNA adenosine deaminase, called DRAD-binding Z-DNA. There are evidences that topoisomerase II from Drosophila, hiunan and calf thymus recognizes a number of DNA shapes, including Z-DNA [34,35]. Bloomfield and coworkers [36] have found that the condensation of plasmids is enhanced by Z-DNA conformation in d(CG)n repeats. The information related to B-Z transition [31], the effect of ligands on it [28,29] and X-ray crystal structure data [37,38] appear to suggest that the possible biological role of this polymorphic form of DNA will be soon established. 

The reaction of the cyclic P3-ligand l,3,5-triphospha-2,4,6-trisilacyclohexane with AgOTf results in the synthesis of complex (101) with a cyclic P6 ligand.794 Optically pure (S,5)-(+)-(PPh2CH2CH2)2(PPhCH2CH2PPh) spontaneously self-assembles into left-handed double-stranded D2-double helix (102) and C2-side-by-side helix conformers of the disilver(I) cation.795... 

Xanthan is reported to undergo a chiroptically detected temperature or salt-driven conformational change from an ordered conformation at high salt and low temperature to a disordered conformation either associated with lowering the salt concentration, or with increasing the temperature (2-5). The primary structure of xanthan has been known for about a decade (6,7), but different structures have been suggested both for the ordered and disordered conformation. Some workers (8-13) conclude that the ordered conformation is double-stranded or double-helix, whereas others (14-17) claim that a single stranded description can account for the observed data under... 

Disordered conformation. Figure 5 shows electron micrographs of xanthan D and F obtained from xanthan vacuum-dried from solutions yielding the disordered conformation. The various molecular assemblies are assigned as follow I = single -stranded, II = perfectly matched double stranded, III = branched from double - to single stranded. This assignment will be discussed below. 

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