A 500-MHz 'H-NMR study on a double-stranded non-self-complementary DNA undecamer comprising a portion of the specific target site for the cyclic AMP receptor protein in thegal operon is presented. Using pre-steadystate nuclear Overhauser effect (NOE) measurements, all exchangeable imino, non-exchangeable base, methyl, and HI', H2' and H2" sugar proton resonances are assigned in a sequential manner. In addition, some of the H3' sugar proton resonances are also assigned and some of the exchangeable amino proton resonances identified. The relative magnitudes of the intranucleotide and internucleotide NOES are indicative of a right-handed B-type conformation for the duplex undecamer in solution.The CAMP receptor protein (CRP) regulates the transcription of at least 20genes in Escherichia coli, including all catabolite-repressible operons, by binding to specific DNA sites in the presence of CAMP [l-41. In some cases this interaction stimulates transcription, as in the case of the lac [5] and ara [6] operons; in other cases it inhibits transcription as in the case of the CRP structural gene [7] and the ornpA gene [S]. In the case of the gal operon binding of the CAMP. CRP complex to a single site exerts opposing effects on the P, and P, promotors, stimulating transcription from the former and inhibiting transcription from the latter [9]. The mechanisms whereby the CAMP. CKP complex exerts these effects are unknown although numerous hypotheses have been put forward [lo-141.From the structural view point, circular dichroic studies have shown that the binding of the CAMP. CRP complex to short oligonucleotides comprising portions of the specific target sites in the gal and lac operons induces a B to C transition in the structure of the DNA, leaving the handedness of the helix, namely right-handed, unchanged [I 5,161. These findings on small oligonucleotides are completely consistent with the observation that the supercoil unwinding of plasmid DNA achieved by the specific DNA binding of the CAMP. CRP complex is less than 0.5 turn [17]. These results are also consistent with those of DNA melting studies on a 301-basepair fragment containing the lac control region which demonstrated that the binding of the CAMP. CRP complex specifically stabilizes a region of about 36-base-pairs [18].A deeper understanding of the structural aspects of CRP . DNA interactions can potentially be achieved by two Abbreviations. CRP, CAMP receptor protein of Escherichia coli (also known as catabolite activator protein or CAP); NOE, nuclear Overhauser effect; 1 1 mer, undecamer ; HPLC, high-pressure liquid chromatography.complementary techniques, namely X-ray crystallography and NMR spectroscopy. To date, the crystal structure of the CAMP. CRP complex has been solved at 0.29-nm resolution [12,19] and NMR studies on CRP and its N-terminal core aCRP, as well as on their interaction with cyclic nucleotides, have been carried out [20 -221. In the present paper we extend the solution NMR studies to the synthetic DNA undecamer (I Imer) :