This invention provides double-stranded polynucleotides having RNA interference and stable to RNase.The double-stranded polynucleotides and slats thereof are composed of polynucleotides of formulae (I) and (II), which are characterized by (a)-(d):5’ -X-(α-β)q-αp-λm-3’ (I)5’ -δs-(α-β)r-Y-υn-3’ (II)(a) α and β are the different DNA or 2’ -OMeRNA; δ and λ are the same or different DNA or 2’ -OMeRNA; υ is any one of the same or different nucleotide selected from DNA, RNA and 2’ -OMeRNA; X and Y are oligonucleotides consisting of nucleotides selected from the same or different DNA, RNA and modified nucleotides(b) p is an integer of 0 or 1 m is 0 when p is 0 m is an integer of 0 to 5 when p is 1 q is an integer of 3 to 9 the sum of nucleotide numbers for (α-β)qand X is 17 to 18 s is an integer of 0 or 1 n is an integer of 0 to 5 r is an integer of 3 to 9 the sum of nucleotide numbers for (α-β)rand Y is 17 to 18(c) the X-(α-β)q-αpin nucleotides of formula (I) is composed of nucleotides sequences equal to the target gene and(d) the nucleotides sequences of X-(α-β)qin nucleotides of formula (I) are complementary to the nucleotides sequences of (α-β)r-Y in nucleotides of formula (II).提供對RNA分解酵素安定之具有RNA干擾作用之雙股多核苷酸等。提供具有由以下(a)至(d)構成之特徵之由式(I)所示之多核苷酸以及式(II)所示之多核苷酸構成之雙股多核苷酸或其鹽等:5’-X-(α-β)q-αp-λm-3’(I)5’-δs-(α-β)r-Y-υn-3’(II)(a)α及β表示不同的DNA或2’-OMeRNA,δ及λ表示相同或不同的DNA或2’-OMeRNA,υ表示相同或不同之選自DNA、RNA及2’-OMeRNA之任一之核苷酸,X及Y表示由選自DNA、RNA及修飾核酸之相同或不同種類之核苷酸構成之寡核苷酸;(b)p表示0或1之整數;p為0時,m為0;p為1時,m表示0~5之任一之整數。q表示3~9之任一之整數;(α-β)q與X的合計核苷酸數為17至18。s表示0或1之整數,n表示0~5之任一之整數。r表示3~9之任一之整數,(α-β)r與Y的合計核苷酸數為17至18;(c)式(I)所示之多核苷酸中,X-(α-β)q-αp是由與標的基因相同之核苷酸序列所構成;(d)式(I)中之X-(α-β)q與式(II)中之(α-β)r-Y是由彼此互補的核苷酸序列所構成。
