Open AccessA Small‐Angle X‐Ray Scattering Study on Poly[d(A‐T) · d(A‐T)], Poly[d(A‐s 4 T) · d(A‐s 4 T)] and Poly[d(A‐s 4 U) · d(A‐s 4 U)]
Author(s) -
Zipper Peter
Publication year - 1973
Publication title -
european journal of biochemistry
Language(s) - English
Resource type - Journals
eISSN - 1432-1033
pISSN - 0014-2956
DOI - 10.1111/j.1432-1033.1973.tb03148.x
Subject(s) - radius of gyration , scattering , crystallography , small angle scattering , physics , radius , scattering length , analytical chemistry (journal) , chemistry , materials science , polymer , nuclear magnetic resonance , optics , computer security , chromatography , computer science
A small‐angle X‐ray scattering study was performed with solutions of the alternating polydeoxynucleotide poly[d(A‐T) · d(A‐T)] and its analogs poly[d(A‐s 4 T) · d(A‐s 4 T)] and poly[d(A‐s 4 U) · d(A‐s 4 U)]. At low concentration of NaCl and neutral pH almost identical results were obtained for these polydeoxynucleotides. At small scattering angles the same cross section radius of gyration R c = 0.92 ± 0.03 nm for all three polydeoxynucleotides was derived from the scattering curves. At larger scattering angles a second cross‐section radius of gyration R c2 could be determined which amounts to 0.855 ± 0.02 nm for poly[d(A‐T) · d(A‐T)], 0.86 ± 0.01 nm for poly‐[d(A‐s 4 T) · d(A‐s 4 T)] and 0.82 ± 0.01 nm for poly[d(A‐s 4 U) · d(A‐s 4 U)], respectively. The length per nucleotide pair, 0.33 ± 0.03 nm, was found to be the same for all three polydeoxynucleotides. These results are similar to those for natural DNA. The above results for poly[d(A‐s 4 T) · d(A‐s 4 T)] and poly[d(A‐s 4 U) · d(A‐s 4 U)] refer to the modification of these polydeoxynucleotides which prevails at low concentrations of 1:1 electrolytes and was designated as helix I. The length per nucleotide pair obtained in this study appears to be consistent with the presence of strong 0 0 8 and 0 0 16 reflections in the high‐humidity X‐ray fibre diffraction patterns for the sodium salt of poy[d(A‐s 4 T) · d(A‐s 4 T)]. The values for the cross‐section radii of gyration, on the other hand, seem to be inconsistent with the reversed Hoogsteen base‐pairing scheme proposed for poly[d(A‐s 4 T) · d(A‐s 4 T)] and poly[d(A‐s 4 U) · d(A‐s 4 U)], because the similarity of these values to those for poly[d(A‐T) · d(A‐T)] and natural DNA is contrary to the results of theoretical calculations on models built up from reversed Hoogsteen base‐pairs. According to these calculations, the cross‐section radius of gyration of poly‐[d(A‐s 4 T) · d(A‐s 4 T)] ought to be smaller than that of natural DNA by about 0.16–0.2 nm if this polydeoxynucleotide really were of the reversed Hoogsteen type.