Observation of arginyl-deoxyoligonucleotide interactions in TaqI endonuclease by detection of specific ¹H NMR signals from 140kD [Nη1, Nη2, ¹⁵N Arg]TaqI/oligomer complexes

Proton and nitrogen signals of the guanidinium amines in [Nη1, Nη2 ¹⁵N Arg]TaqI endonuclease were observed using isotope filtered experiments and proton detected ¹H{¹⁵N} heterocorrelated two dimensional NMR spectroscopy. These rapidly exchanging protons could be detected in the free enzyme only at pH 4.5; at pH 8.5, no signals were measured after extensive signal averaging. Addition of deoxyribonucleotide oligomers resulted in the appearance of two groups of signals at about 6.8 and 7.5 ppm. Since these signals are independent of the presence of cognate sequence or Mg²⁺, it is assumed they represent nonspecific arginyl-DNA interactions. This labeling/NMR approach provides a new method for investigating the role of arginine in protein-DNA interactions.