It may not have eyes, but the saltwater Natronobacterium pharaonis has a primitive form of vision that uses blue-light-absorbing sensory rhodopsin II proteins (SRII) embedded in its membrane bilayer. When activated, SRII sends signals that are "translated into flagellar motion," says Harmut "Hudel" Luecke, professor of molecular biology and biochemistry, University of California, Irvine. SRII's signaling enables bacteria to swim away from harsh sunlit areas where blue light would otherwise cause significant damage. Until recently, scientists have understood little about how SRII functions, or even what it looks like. Last month, Luecke and his UC-Irvine colleagues and others at the University of Texas Medical School reported the first high-resolution crystal structure of SRII (Science Express: SRII's peculiar aspect, says Luecke, is that even though its chromophore--a vitamin A derivative--is chemically identical to that of other rhodopins, the latter absorb green-orange light at 570 to 590 nm,...

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