X-ray diffraction from the side-by-side model of DNA

Publisher Website
Google Scholar
Abstract
An intriguing topological problem posed by the double-helical Watson–Crick1 model of DNA is that of unwinding the intertwined strands during replication. Several workers have recently proposed novel side-by-side (SBS) structures for DNA2–6. In all these models the two strands are joined by complementary Watson–Crick base pairs and the antiparallel polynucleotide strands alternate between short segments of right- and left-handed helix, thus both reducing the amount of intertwining and alleviating the unwinding problem. We show here that there are unacceptable discrepancies between the observed diffraction pattern of B-DNA7 and that calculated for the original SBS structure2. We also describe a simple modification of this model which resolves some of the more serious discrepancies. However, the agreement is still markedly inferior to that obtained for a Watson–Crick model of DNA.