Physical Studies of N-Acetoxy-N-2-Acetylaminofluorene-Modified Deoxyribonucleic Acid

Denatured T4 phage DNA was reacted with N-acetoxy-N-2-acetylaminofluorene. The rate of reaction war determined using the change in the melting temperature of renatured DNA as an indicator of the percentage of modification. The renaturation rates of a series of modified DNAs were investigated. This rate is reduced by a factor of 2 when the melting temperature is lowered 15°. The absorption at 305 nm, the negative circular dichroism band around 300 nm, the melting temperature change, and the buoyant density shift due to modification were investigated. From these data, we conclude that the melting temperature change due to 1 % modified base pairs is 0.9°. Electric dichroism of modified DNA was studied in an alternating field. From the dichroism, we calculate the angle between the aminoacetylfluorene residue 305-nm transition moment and the DNA helix axis to be 60 ± 4° under conditions where the 305-nm band is optically active. The aminoacetylfluorene residue must be located in an asymmetric potential field outside of the DNA helix.