Single-stranded nucleic acid molecule having delivery function and gene expression regulating ability

A single-stranded nucleic acid molecule for inhibiting expression of a target gene, which consists of a region (X), a linker region (Lx) and a region (Xc), wherein

• said region (X) is complementary to said region (Xc),
• at least one of said region (X) and said region (Xc) comprises an expression inhibitory sequence that inhibits expression of the target gene,
• said linker region (Lx) comprises formula (I-4):
• wherein n is an integer from 0 to 30, and m is an integer from 0 to 30,
• a bio-related substance having a delivery function is bonded to formula (I-4) in said linker region (Lx) of the single-stranded nucleic acid molecule for inhibiting expression of a target gene,
• said bio-related substance is a lipid,
• said region (Xc) is perfectly complementary to the entire region or part of the said region (X),
• said region (X) consists of any of the following residues (1) to (3):
• (1) an unmodified nucleotide residue(s), (2) a modified nucleotide residue(s), and (3) an unmodified nucleotide residue(s) and a modified nucleotide residue(s), and
• the base number (X) of said region (X) and the base number (Xc) of said region (Xc) satisfy the formula:
• X-Xc=1 or 2.