title: Highly selective chemical modification of cruciform loops by diethyl pyrocarbonate.
abstract: Diethyl pyrocarbonate reacts with the single-stranded loops of cruciform structures with great selectivity. Adenine bases are carbethoxylated, as a result of which the backbone may be cleaved with piperidine, and the level of chemical modification at each base may be determined. We have studied the ColE1 and (A-T)34 cruciforms of pColIR315 and pXG540. In each case we observe maximal modification at the most central adenosine of the loop, and an overall pattern of modification corresponding to a total loop size of about six bases. The results may be interpreted in terms of a model in which the loop has a defined tertiary structure. No modification was detected at either cruciform four-way junction, suggesting that this region is fully base-paired.
mesh_terms: D001483:Base Sequence; D004247:DNA / Q000032:analysis*; D004262:DNA Restriction Enzymes / Q000378:metabolism; D004269:DNA, Bacterial / Q000032:analysis; D004277:DNA, Single-Stranded / Q000032:analysis; D004278:DNA, Superhelical / Q000032:analysis; D015245:Deoxyribonuclease BamHI; D015246:Deoxyribonuclease EcoRI; D004047:Diethyl Pyrocarbonate; D004587:Electrophoresis, Agar Gel; D004926:Escherichia coli / Q000235:genetics; D005561:Formates; D009690:Nucleic Acid Conformation
chemical_list: D004269:DNA, Bacterial; D004277:DNA, Single-Stranded; D004278:DNA, Superhelical; D005561:Formates; D004247:DNA; D004262:DNA Restriction Enzymes; D015245:Deoxyribonuclease BamHI; D015246:Deoxyribonuclease EcoRI; D004047:Diethyl Pyrocarbonate