Crossing the borders: archaeal rhodopsins go bacterial

All-trans-retinal based, light-driven ion pumping and light sensing are no longer an exclusive archaeal enterprise after the exciting discovery of archaeal-type rhodopsins in bacteria and eukarya. Following the discovery of proton-pumping rhodopsins in marine bacteria (proteorhodopsins), an archaetypal system, consisting of a membrane-intrinsic sensory rhodopsin and a soluble interacting transducer, was recently identified in the cyanobacterium Anabaena. The powerful approach that combines genome ‘digging’ and protein expression is rapidly changing our understanding of light responses in lower organisms.