ATP synthase 5' untranslated regions are specifically bound by chloroplast polypeptides

Expression of the large ATP synthase gene cluster in spinach (Spinacia oleracea) chloroplasts is regulated at the post-transcriptional level. RNA stability and the translational efficiency of some chloroplast transcripts have been shown to be regulated through RNA-protein interactions in the 5' untranslated region (5' UTR). In this report we show that spinach chloroplast extracts contain polypeptides that specifically interact with the 5' UTRs of three of the four genes in the large ATP synthase gene cluster. A subset of binding polypeptides may be gene-specific, although at least one appears to be a more general chloroplast RNA-binding protein. We hypothesize that these RNA-protein interactions may affect the expression of this gene cluster from two perspectives. The first would be at a gene-specific level, which could serve to control the stoichiometry of ATP synthase subunits. The second would be a more global effect, which may adjust the abundance of the entire ATP synthase complex in response to environmental or developmental cues.