Abstract
Many cyanobacteria show phototactic motility by employing pilus structures. Synechocystis sp. PCC 6803 has been a model organism for molecular analysis of genes involved in such photoresponses. Previously, we isolated SyPixJ1 protein that serves as a photoreceptor for positive phototaxis and showed the reversible photoconversion between 435 nm and 535 nm forms (Yoshihara et al. 2004 PCP). However, purification was not sufficient to eliminate any other pigments from the preparations because it is expressed in membranes. Here, we expressed in Synechocystis a chromophore-binding domain of TePixJ from a thermophilic cyanobacterium Thermosynechococcus elongatus strain BP-1. The purified TePixJ_GAF with a His-tag showed the same blue-green reversible photoconversion as SyPixJ1. By contrast, TePixJ_GAF did not show spontaneous dark reversion. These results clearly demonstrated that the unique photoreversible cyanobacteriochrome serves as a photoreceptor for phototactic motility widely in cyanobacteria.
