THE BINDING OF THE ANTITUMOR ANTIBIOTIC CHARTREUSIN TO POLY(dA-dT)•POLY(dA-dT), POLY(dG-dC)•POLY(dG-dC), CALF THYMUS DNA, TRANSFER RNA, AND RIBOSOMAL RNA

Abstract

Chartreusin binds cooperatively to poly(dA-dT)•poly(dA-dT)and poly(Dg-dC)•poly(dG-dC). Both the site-exclusion model and the specific site model yield cooperative binding constants of about 5×105M^-1 and 3×105 M^-1 for the AT and GC polymers, respectively, and the same stoichiometry and intrinsic binding constant for both polymers of 5 nucleotides per binding site and 3.1×104M^-1, The Scatchard plot for calf thymus DNA is curved in the opposite sense from that of cooperative binding. These binding data did not fit the site-exclusion model with the cooperative binding parameter as a variable nor the specific site, negative-cooperative binding model The site-exclusion model with a cooperative binding parameter of unity yielded a binding constant of about 4×104M^-1 and a stoichiometry of about 5 nucleotides per binding site. The same model for transfer and ribosomal RNA yielded binding constants of 5×103 M^-1 and 7×103 M^-1 and stoichiometries of about 13 and 6 nucleotides per binding site, respectively.