Abstract: An object is to provide a technique that can enhance the binding properties of a single-stranded polynucleotide comprising a palindromic structure comprising an acyclic polynucleotide structural unit to target polynucleotides, such as miRNA, while suppressing self-duplex formation of the single-stranded polynucleotide. This object is achieved by a single-stranded polynucleotide comprising a palindromic structure comprising an acyclic polynucleotide structural unit, wherein adenine in the palindromic structure is replaced by diaminopurine, and thymine at a position complementary to the adenine is replaced by a thiouracil derivative.

Abstract: An agent for inhibiting the action of a target RNA based on RNA interference and ASO with a passenger strand and a guide strand for a target RNA, wherein both ends of double-stranded RNA formed pairing of the passenger strand and the guide strand are blunt ends, and one or two or more selected from the group consisting of the units represented by formula (1) and formula (2) below at the following positions (a) and (b): (a) 5? end side and 3? end side of the passenger strand, (b) 3? end side of the guide strand (in which X represents an oxygen atom or sulfur atom), (in which X represents an oxygen atom or sulfur atom).