Circular Dichroism and Conformation of Natural and Synthetic Polynucleotides***

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Abstract
The relation between conformations of several natural and synthetic polynucleotides and their circular dichroism was studied. It has been revealed that the magnitude of circular dichroic band around 265 μ decrease remarkably when base-stacking of polynucleotides was destroyed. When base pairing between two strands of polynucleotides was ruptured the peak of circular dichroic band was shifted toward a longer wave length side. The content of the ordered structure obtained by the magnitude of circular dichroic band was in good agreement with that obtained by hypochromic effect. Circular dichroism of poly A in neutral solution and at room temperature manifested that poly A was mostly in a single stranded helical conformation while poly U in neutral solution and at room temperature had very small content of helical conformation. Very sharp decrease of circular dichroism was observed when poly (A+U) was heated to61°, which reflected that poly (A+U) was in a double stranded helical structure at lower temperature. Several kinds of RNAs including t-RNA, ribosomal RNA and RDV RNA were characterized on circular dichroism. Among those, RDV RNA was most striking. Very large amplitude in circular dichroic band and quite sharp heat transition observed both on circular dichroism and hypochromism manifested that this RNA was in double stranded helix. Helical content of several RNAs was estimated assuming RDV RNA in 100% helical conformation. The results obtained were in fairly good agreement with those obtained by hypochromicity. DNA had characteristic circular dichroic features in its low magnitude and 243 μ negative band. Circular Dichroism- and Conformation of Polynucleotides The sharp band observed for circular dichroism has manifested its strong advantage in its application on the system which contain both polynucleotides and proteins. Taking this advantage the conformations of t-RNA, ribosomal RNA and DNA were studied when they were complexed with proteins.