1H NMR studies of lac-operator DNA fragments.

The hydrogen-bonded imino protons of a 14 base pair double-stranded DNA fragment comprising one half of the lac operator of E. coli were investigated by 360 MHz H NMR. From combined melting studies of this synthetic 14 b.p. fragment and its two constituent 7 b.p. fragments a nearly complete assignment for the low-field proton resonances was obtained. The experimental spectra are compared with calculated spectra and with the spectrum of a 51 b.p. DNA restriction fragment from E. coli containing the complete lac operator. Structural information on these oligonucleotides is presented. This study is a prerequisite for future 1H NMR investigations of the interaction of the lac operator with the lac repressor.