Genetic engineering of phytochrome biosynthesis in bacteria

The bilin prosthetic groups of the phytochrome photoreceptors and the light -harvesting phycobiliprotein antennae arise from the oxygen-dependent ring opening of heme. Two ferredoxin-dependent enzymes contribute to this conver sion: a heme oxygenase and a bilin reductase with discrete double-bond spec ificity. Using a dual plasmid system, one expressing a truncated cyanobacte rial apophytochrome 1, Cph1(N514), and the other expressing a two-gene oper on consisting of a heme oxygenase and a bilin reductase, these studies esta blish the feasibility of producing photoactive phytochromes in any heme-con taining cell. Heterologous expression systems for phytochromes not only wil l facilitate genetic analysis of their assembly, spectrophotometric activit y, and biological function, but also might afford the means to regulate gen e expression by light in nonplant cells.