Self-assembly of synthetic phytochrome holoprotein in vitro.

The phytochrome holoprotein of plants requires a covalently bound linear tetrapyrrole (bilin) prosthetic group for its photoreceptor function. Here we show that synthetic phytochrome apoprotein prepared by transcription and translation of an Avena phytochrome cDNA construct combines in vitro with phycocyanobilin, an analog of the natural chromophore, to produce a photoactive holoprotein. These results indicate that holoprotein assembly is an "autocatalytic" process.