Enzymatic sequence-specific spin labeling of a DNA fragment containing the recognition sequence of EcoRI endonuclease.

Deoxyuridine analogs spin labeled in position 5 have been enzymatically incorporated sequence specifically into an oligodeoxyribonucleotide to form a spin-labeled 26-mer. The 26-mer contains the EcoRI-binding site and two labels which are located symmetrically close to the binding site. The labels are separated from one another far beyond the Heisenberg spin-exchange distance. The local base motion as determined by ESR spectroscopy is of the order of 4 ns in the oligonucleotide duplex. This is the same value as reported earlier for local T motions in polynucleotide duplexes, thereby providing direct experimental evidence that the ESR line shape of spin levels covalently attached to nucleic acids depends primarily on the local dynamics of the nucleic acid building blocks.