Structure of a glutathione peroxidase homologous gene involved in the oxidative stress response in Chlamydomonas reinhardtii

The organisation and nucleotide sequence of the single copy glutathione per oxidase homologous gene gpxh from Chlamydomonas reinhardtii is reported. Th e gpxh gene consists of five exons and four introns, and encodes a predicte d protein (GPXH) of 162 amino acids. GPXH belongs to the family of glutathi one peroxidase (GPX)-like proteins and showed high homology with the deduce d amino acid sequences of gpx-related genes from yeast (67-78% similarity) and from plants (60-65% similarity). The GPXH from C. reinhardtii differs f rom the well characterized mammalian cytosolic GPX (GPX1) in that it contai ns a normal cysteine residue instead of a selenocysteine, that the residues responsible for glutathione binding at the reactive center in GPX1 are not present, and that two amino acid stretches important for the tetramerisati on of GPX1 are absent. Northern blot experiments revealed a single 1.3 kb m RNA of which the cellular concentration is elevated strongly upon exposure to chemicals causing oxidative stress. In addition, salt stress did cause a weak increase in mRNA concentration. This indicates that gpxh is an oxidat ive stress responding gene rather than a general stress responsive gene. (C ) 1999 Elsevier Science Ireland Ltd. All rights reserved.