A U.S.-Russian team of scientists has created the first red mutant of the jellyfish green fluorescent protein (GFP), a widely used biological marker (Biochemistry, DOI: 10.1021/bi702130s). Although red fluorescent proteins for cellular labeling are available from other organisms, the ease of expressing GFP in any organism makes a red GFP mutant desirable. The team, led by Vladislav V. Verkhusha of Albert Einstein College of Medicine, in New York City, and Konstantin A. Lukyanov of the Shemiakin-Ovchinnikov Institute of Bioorganic Chemistry, in Moscow, found red GFP mutants after multiple rounds of random mutagenesis of GFP-expressing bacteria and high-throughput screening of the resulting protein variants. The structure of the brightest red fluorescent mutant protein is shown, with the amino acids of the chromophore highlighted. This protein actually emits both red and green light. "This mutant is the first step toward the ideal monomeric red fluorescent protein," Verkhusha says. "We plan to continue our work to make the mutant absolutely red without any green component."