Interactions of hormonal steroids with nucelic acids. I. A specific requirement for guanine.

Under equilibrium conditions testosterone, progesterone, estradiol, and corticosterone bind to denatured but not to native DNA. Among synthetic polynucleotides, steroids bind only to guanine containing polymers:poly dG, poly G, poly UG, poly AG, and "denatured" poly dG:dC; however, they do not bind to rRNA, sRNA, TMV-RNA, poly CG, or native poly dG:dC. These data indicate a preferential affinity for guanine residues and for single-stranded regions of polynucleotides. That different functional groups of the purine are involved in the associations with different steroids is indicated by the observation that only estradiol binds to poly I. Restrictions are also imposed by structural attributes of the steroids: an alpha-substitution at C-17 reduces binding, polyhydroxylated steroids bind poorly or not at all.