Phosphorothioate analogs of 2',5'-oligoadenylate. Activation of 2',5'-oligoadenylate-dependent endoribonuclease by 2',5'-phosphorothioate cores and 5'-monophosphates

The preceding paper in this issue described the synthesis and structural elucidation of the phosphorothioate analogues of 2',5'-oligoadenylate (2-5A) dimer and trimer cores [Karikó, K., Sobol, R. W., Jr., Suhadolnik, L., Li, S. W., Reichenbach, N. L., Suhadolnik, R. J., Charubala, R., & Pfleiderer, W. (1987) Biochemistry (preceding paper in this issue)]. In this report, the binding and activation processes of 2-5A-dependent endoribonuclease (RNase L) have been examined by using four diastereomeric 2',5'-phosphorothioate trimer core analogues and their 5'-monophosphates. These 2',5'-phosphorothioates have revealed a distinct separation of the structural parameters that govern binding vs activation of RNase L. Radiobinding assays have demonstrated that extensive stereochemical modification of the internucleotide linkages of 2-5A is possible without adversely affecting its ability to bind to RNase L. However, a marked difference was observed in the activation of RNase L by the stereochemically modified 2-5A molecules as determined in core--cellulose and rRNA cleavage assays. Three of the four 2',5'-phosphorothioate trimer cores (with RpRp,SpRp, and RpSp internucleotide linkages) are the first 2-5A core molecules able to activate RNase L. For example, the RpRp, SpRp, and RpSp diastereoisomers activate RNase L to hydrolyze poly(U)-3'-[32P]pCp 65%, 20%, and 15%, respectively, at 5 X 10(-5) M. The SpSp diastereomer cannot activate RNase L. The order of RNase L activation was the same for the core analogues and their 5'-monophosphates (RpRp greater than SpRp greater than RpSp).(ABSTRACT TRUNCATED AT 250 WORDS)