The vacuum UV CD bands of repeating DNA sequences are dependent on sequence and conformation.
CD spectra were obtained for eight synthetic double-stranded DNA polymers down to at least 175 nm in the vacuum uv. Three sets of sequence isomers were studied: (a) poly[d(A-C).d(G-T)] and poly[d(A-G).d(C-T)], (b) poly[d(A-C-C).d(G-G-T)] and poly[d(A-C-G).d(C-G-T)], and (c) poly[d(A).d(T)], poly[d(A-T).d(A-T)], poly[d(A-A-T).d(A-T-T)], and poly[d(A-A-T-T).d(A-A-T-T)]. There were significant differences in the CD spectra at short wavelengths among each set of sequence isomers. The (G.C)-containing sequences had the largest vacuum uv bands, which were positive and in the wavelength range of 180-191 nm. There were no large negative bands at longer wavelengths, consistent with the polymers all being in right-handed conformations. Among the set of sequences containing only A.T base pairs, poly[d(A).d(T)] had the largest vacuum uv CD band, which was at 190 nm. This CD band was not present in the spectra of the other (A.T)-rich polymers and was absent from two first-neighbor estimations of the poly[d(A).d(T)] spectrum obtained from the other three sequences. We concluded that the sequence dependence of the vacuum uv spectra of the (A.T)-rich polymers was due in part to the fact that poly[d(A).d(T)] exists in a noncanonical B conformation.
Gray
D M
DM
Program in Molecular and Cell Biology, University of Texas, Dallas 75083-0688.
Johnson
K H
KH
Vaughan
M R
MR
Morris
P A
PA
Sutherland
J C
JC
Ratliff
R L
RL
D001482:Base Composition; D001483:Base Sequence; D002942:Circular Dichroism; D004247:DNA; D008969:Molecular Sequence Data; D009690:Nucleic Acid Conformation; D011119:Polynucleotides; D013056:Spectrophotometry, Ultraviolet
D011119:Polynucleotides; D004247:DNA