Relationship between two tandemly arranged and light-induced glutathione S-transferase genes from the ciliated protozoa Blepharisma japonicum

Abstract

Recently we reported a light-induced cDNA encoding glutathione S-transferase (GST) from the ciliated protozoa Blepharisma japonicum, which possessed photosensitive pigments. In this study, a novel cDNA encoding GST was further isolated, and the two GSTs (BjGST1 and BjGST2) showed high sequence identity of 86%. Phylogenetic trees indicated that the BjGSTs were distantly related to known classes of GSTs, and they could form a protozoa-specific class. The recombinant proteins also existed as homo- or heterodimers that exhibited different enzyme activities, appreciating the functional differentiation. Furthermore, the transcription levels of BjGST genes were coordinately regulated in response to light stimulation. In addition, the genomic structure analysis revealed that the two genes were tandemly arranged through an approximately 500-bp spacer region of unusual DNA structure containing cis-acting elements related to oxidative stress response. These results demonstrate that the two BjGSTs are expressed simultaneously and act cooperatively against photooxidative stress.