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1993 (1)
1988 (1)
1Author    CherlaP. Murthy, DavidJ. Deeble, Clemens Von SonntagRequires cookie*
 Title    The Formation of Phosphate End Groups in the Radiolysis of Polynucleotides in Aqueous Solution  
 Abstract    The polynucleotides poly(U), poly(C), poly(A) and poly(G) have been y-irradiated in N20-and N20/02 (4:l)-saturated aqueous solutions. Hydroxyl radicals from the radiolysis of water react with the polynucleotides thereby producing among other lesions strand breaks. Strand break-age is connected with the formation of phosphomonoester end groups. Such end groups have been determined by measuring inorganic phosphate after a three hour incubation at 37 °C with acid or alkaline phosphatase. In the absence of oxygen G(phosphomonoester end groups) (in units of i^mol J' 1) are 0.47 (poly(U)), 0.17 (poly(C)) and < 0.04 (poly(A) and poly(G)). In the case of poly(U) and poly(C) on heating the sample for one hour at 95 °C prior to incubation with phosphatases the above values increased by 0.14 and 0.07 jxmol J" 1 , resp., whereas such treatment of the purine poly-nucleotides still did not produce a measurable yield of phosphomonoester end groups. Comparing these values with G values for strand breakage taken from the literature, about two phospho-monoester end groups are formed per strand break in poly(U) while for poly(C) this ratio is about unity. The purine polynucleotides show very low yields of strand breakage in agreement with the negligible phosphomonoester yields. In the presence of oxygen G(phosphomonoester end groups) are 0.46 (poly(U)), 0.21 (poly(C)), and < 0.04 (poly(A) and poly(G)). On heating, these values increase, most markedly for poly(U) and poly(C). This is possibly linked to the decomposition of unstable hydroperoxides which are formed in high yields in poly(U) and poly(C) (G = 0.7 and 0.19 nmol J resp.). It is known that at least in the case of poly(U), base radicals attack a sugar moiety and are the main precursors of these lesions. G(phosphomonoester end groups) are considerably lower in the case of the purine polynucleotides. Whether this is due to an inability of the base radicals to attack a sugar moiety or has other reasons must remain an open question. 
  Reference    Z. Naturforsch. 43c, 572—576 (1988); received March 14 1988 
  Published    1988 
  Keywords    Polynucleotides, Strand Break, Phosphomonoester End Group, Oxygen Effect 
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 TEI-XML for    default:Reihe_C/43/ZNC-1988-43c-0572.pdf 
 Identifier    ZNC-1988-43c-0572 
 Volume    43 
2Author    SeungR. Yong, D. Ieter, W. G. Ruenw EdelRequires cookie*
 Title    Differential Effect of Hg(II) on [d(A)n * d(T)n] and [d(A-T)n * d(A-T)n] Sequences: Circular Dichroism (CD) Measurements and Endonuclease Digestion Studies Using Poly|d(A) * d(T)] and Poly[d(A-T) * d(A-T)] as Substrates  
 Abstract    The long-wavelength positive CD bands o f poly[d(A) • d(T)] and poly[d(A-T)-d(A-T)] be­ come inverted upon the addition of Hg(C104)2. Poly[d(A)-d(T)] requires higher levels of mer­ cury to undergo inversion than poly[d(A-T)-d(A-T)]\ Mercurated poly[d(A) d(T)] is digested more rapidly than the control by DNase I or staphylococcal nuclease at low levels of Hg(C104)2. Let r = [Hg(C104)2]added/[DNA-P]. A 4-to 5-fold rate increase occurs with DNase I at r = 0.25; a 2-fold increase with staphylococcal nuclease at r = 0.2. By contrast, digestion of poly[d(A-T) d(A-T)] decreases immediately with increasing r. The noted rate increases appear to be due to a modification of poly[d(A)-d(T)] helix structure prior to the chiroptical conver­ sion. The modification is interpreted as a widening of the minor groove, permitting, thus, a better binding of DNase I to its substrate. The overall changes in CD as well as enzymatic digestion rates are taken to signal mercury-induced alterations in helix screwness from right-to-left. They are totally reversible subsequent to the removal o f mercury. 
  Reference    Z. Naturforsch. 48c, 488—494 (1993); received September 18 1992/February 2 1993 
  Published    1993 
  Keywords    Circular Dichroism, Endonucleases, Polynucleotides, Mercury Complexes, Right«-*Left Inversions 
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 TEI-XML for    default:Reihe_C/48/ZNC-1993-48c-0488.pdf 
 Identifier    ZNC-1993-48c-0488 
 Volume    48