Phosphorus NMR of plasmid DNA.

Due to the key position of phosphorus-containing compounds in biology, favour­ able NMR properties of 3 I P nucleus and its 100 % natural abundance, 3 1 P NMR has become a valuable biochemical method. It gives, for example, information about DNA conformation since 3 I P NMR chemical shift is sensitive to the phosphodiester linkage geometry (Gorenstein 1984). 3 1 P NMR reflects base sequence — dependent structural variations in the classical B-DNA double helix (Patel et al. 1982) and it also distinguishes between various types of DNA double helix (Patel et al. 1979; Shindo et al. 1979; Kypr et al. 1981; Vorlíčková et al. 1983). Studies carried out so far have almost been restricted to short DNA fragments of nucleosomal length since resonances of longer fragments were too broad to be measured with a sufficient signal-to-noise ratio (Hanlon et al. 1976; Kypr, Sklenár and Vorlíčková, unpublished results). An extrapolation of results obtained with linear DNA fragments of various lengths has almost excluded obtaining 3 1 P NMR of 5 —10 kilobase phage or plasmid DNAs. Surprisingly, a 3 1 P NMR spectrum of 7 kilobase pins 36 plasmid DNA has recently been reported (Bendel et al. 1982). However, its signal to noise ratio was very low so that the resonance amplitudes could only be determined. No other 3 1 P NMR spectrum of plasmid DNA has since been published. We show here that a signal-to-noise ratio comparable to that obtained with short linear DNA fragments can also be obtained in the 3 , P NMR spectrum of plasmid DNA.