A TRIPLEX DNA-STRUCTURE OF THE POLYPYRIMIDINE - POLYPURINE STRETCH INTHE 5'-FLANKING REGION OF THE SEA-URCHIN ARYLSULFATASE GENE

Previously we reported that a long (522 bp) polypyrimidine: polypurine stretch in the 5' flanking region of the arylsulfatase gene of the se a urchin, Hemicentrotus pulcherrimus, took an unusual, perhaps tripler , DNA structure, when subjected to an acidic pH (pH 5) (Yamamoto et at , 1994). In the present study we have isolated a polypyrimidine: polyp urine containing fragment from the arylsulfatase gene and surveyed the sensitivities of the polypyrimidine: polypurine stretch to base modif ication by diethylpyrocarbonate and osmium tetroxide under various lev els of negative supercoiling. Based on the sensitivity of highly negat ively supercoiled DNA to these base-modifying reagents, we conclude th at, when highly negatively supercoiled, the polypyrimidine: polypurine stretch can take a tripler DNA structure even at a neutral pH and und er physiological ionic strength in the presence of Mg2+.