Evolutionary tinkering: birth of a novel chloroplast protein.

The term 'evolutionary tinkering' refers to evolutionary innovation by recombination of functional units, and includes the creation of novel proteins from pre-existing modules. A novel instance of evolutionary tinkering was recently discovered in the flowering plant genus Nicotiana: the conversion of a nuclear transcription factor into the plastid-resident protein WIN4 (wound-induced clone 4) involved in environmental stress responses. In this issue of the Biochemical Journal, Kodama and Sano now show that two steps are necessary for the establishment of the novel plastid protein: the acquisition of an internal translation initiation site and the use of multiple transcription starts to produce short mRNA variants that encode the plastid-targeted protein form.