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 peroxidase homologous gene gpxh from Chlamydomonas reinhardtii is reported. The gpxh gene consists of five exons and four introns, and encodes a predicted protein (GPXH) of 162 amino acids. GPXH belongs to the family of glutathione peroxidase (GPX)-like proteins and showed high homology with the deduced amino acid sequences of gpx-related genes from yeast (67-78% similarity) and from plants (60-65% similarity). The GPXH from C. reinhardtii differs from the well characterized mammalian cytosolic GPX (GPX1) in that it contains 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 tetramerisation of GPX1 are absent. Northern blot experiments revealed a single 1.3 kb mRNA 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 oxidative stress responding gene rather than a general stress responsive gene. (C) 1999 Elsevier Science Ireland Ltd. All rights reserved.