The site-specific DNA endonuclease encoded by a group I intron in the Chlamydomonas pallidostigmatica chloroplast small subunit rRNA gene introduces a single-strand break at low concentrations of Mg2+. - Monique Turmel; Jean-Patrick Mercier; Vincent Côté; Christian Otis; Claude Lemieux (Nucleic Acids Res., 1995)