INFRARED SPECTRUM OF A DNA-RNA HYBRID

The infrared absorption spectrum in the 4000–400 cm− region of an oriented film of a DNA–RNA hybrid in its undeuterated and deuterated states was observed with the polarized radiation. Most of the stronger bands found in the double‐helical DNA's and double‐helical RNA's are identified in the spectrum of the hybrid. The absorption band at 1225 cm−1 shows a perpendicular dichroism and that at 1085 cm−1 shows almost no dichroism. These facts indicate that the orientation of the group with respect to the helix axis in the hybrid structure is not entirely the same as that in the double‐helical Na DNA at, 75% RH., although the x‐ray diffraction pattern of the hybrid is quite similar to that of the DNA A form. The PO2− orientation is not the same as that in the double‐helical RNA either. The observed dichroism is explained, however, by considering that the PO2− group in the RNA moiety takes nearly the same orientation as that in the double‐helical RNA, and the PO2− group in the DNA moiety takes nearly the same as that in the double‐helical DNA. Copyright © 1969 John Wiley & Sons, Inc.