Uridine analogs of 2′,5′-oligoadenylates: On the biological role of the middle base of 2-5A trimer

Abstract

In order to further delineate the role of the second nucleotide residue of 2-5A in its interaction with the 2-5A-dependent endonuclease, RNase L, a series of uridine-substituted sequence-specific analogs were synthesized and evaluated for their ability to bind to and activate the nuclease. Substitution of only the 5′-terminal adenosine by uridine caused up to a 100-fold loss in binding and activation of RNase L. Replacement of the middle adenosine residue of 2-5A trimer by uridine also resulted in some loss of binding and activation ability. When the 2′-terminal adenosine was replaced by uridine, a dramatic decrease in activation ability was observed. The results reinforced earlier conclusions that elements of the adenine base of the 5′-nucleotide are involved in binding to the 2-5A-dependent endonuclease, whereas activation is dependent upon structural determinants in the adenine moiety of the third adenosine nucleotide residue of 2-5A. These results also implicated some as yet undefined structural or conformational feature associated with the second nucleotide unit of 2-5A that may be involved in binding to or activation of RNase L.