PROBLEM TO BE SOLVED: To provide RNA complexes with one or more hydroxymethyl substituted monomers incorporated into an RNA strand to be used in relation to RNA-guided gene regulation or gene analysis, in particular RNA interference (RNAi).SOLUTION: The present invention relates to an oligomer comprising one or more 2'-3'-seco-RNA monomer, and the oligomer comprising an RNA double-stranded part with first and second RNA strands, wherein the 2'-3'-seco-RNA monomer is expressed by the following formula monomer D, and at least ona part of the oligomer comprises a target sequence and a complementary sequence. [Base is nucleic acid base]【課題】ＲＮＡ誘導遺伝子調節または遺伝子分析、特に、ＲＮＡ干渉（ＲＮＡｉ）に対して使用するためのＲＮＡ鎖に取り込まれた１個又は複数個のヒドロキシメチル置換モノマーを有するＲＮＡ複合体の提供。【解決手段】１個以上の２’－３’－セコ－ＲＮＡモノマーを含むオリゴマーであって、該オリゴマーは第１及び第２のＲＮＡ鎖を有するＲＮＡ二本鎖部分を含み、該２’－３’－セコ－ＲＮＡモノマーが下式のモノマーＤで表され、且つ、該オリゴマーの少なくとも一部が標的配列と相補的な配列を含む、オリゴマー。［塩基は核酸塩基である］【選択図】なし
