Ultraviolet circular dichroism spectra have been measured for 12 synthetic DNA polymers of defined, simple sequences. This library of spectra has been used to obtain first-neighbor frequency distributions for 6 natural complex DNAs and 14 natural satellite DNAs by computer analysis. Only 3 of the 12 synthetic polymer spectra have not been measured in our own laboratory, and our preliminary work indicates that significant improvement on the published spectra of these polymers is possible. Therefore, as a final stage in achieving the most accurate CD analysis currently possible for double-stranded DNAs, we plan to study the spectra of these polymers (poly(d(A-A-C).d(G-T-T)), poly(d(A-T-C).d(G-A-T)), and poly(d(A-C-T).d(A-G-T)) in detail. In addition, we propose to study the ethanol-condensed forms of double-stranded RNAs and DNAs. DNA can form tertiary supercoils when condensed by ethanol on carbon-coated grids used for electron microscopy (D. Lang, 1974, J. Mol. Biol. approximately 89, 783), and under similar conditions DNA suspensions give a CD spectrum different from the well-known psi-DNA spectrum (Gray and Long, unpublished). We hope to characterize the secondary conformations of DNAs and RNAs in such condensates by electron microscopy, circular dicroism, and other physical techniques. BIBLIOGRAPHIC REFERENCES: Gray, D. M. and Ratliff, R. L. "Circular Dichroism Evidence for G.U an G.T Base Pairing in Poly(r(G-U)) and Poly(d(G-T))" Biopolymers, 1977, in press. Gray, D.M., Hamilton, F. D., and Vaughan, M. R. "The Analysis of Circular Dichroism Spectra of Natural DNA's Using Spectral Components from Synthetic DNA's". Biopolymers, 1977, in press.
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