Aptamer regulated nucleic acids and uses thereof

A nucleic acid comprising:

• (i) an aptamer comprising a 5′-end switching aptamer stem sequence;
• and
• (ii) a 3′-end priming sequence;
• wherein:
• (1) in a first conformation, the 3′-end priming sequence forms a hairpin structure, and the 5′-end switching aptamer stem sequence is single-stranded;
• and,
• (2) in a second conformation, the 5′-end switching aptamer stem sequence hybridizes to a complementary region of the nucleic acid, and the 3′-end priming sequence is available for hybridization to a target template to form a primer:template pair;
• wherein binding to a ligand by the aptamer induces a conformational change of the nucleic acid to shift between the first conformation and the second conformation, or between the second conformation and the first conformation.