Switch-hitter: A new strategy to control gene expression relies on a ligand-dependent, ribozyme-based RNA switch. The key feature of this setup is that the ribozyme liberates the ribosome binding site upon cleavage of the message. The design made it possible to screen in vivo for an inducible aptazyme by attaching an aptamer to stem III of the ribozyme, thus preserving naturally occurring stem I/stem II contacts. Supporting information for this article is available on the WWW under http://www.wiley-vch.de/contents/jc_2002/2008/z703700_s.pdf or from the author. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.