Plastome mutation affecting the chloroplast ATP synthase involves a post-transcriptional defect

In a plastid genome (plastome) mutation of Oenothera hookeri, at least two of the plastome-coded polypeptides (the beta and epsilon subunits) of the chloroplast ATP synthase are directly affected. As in other plastid chromosomes, the genes for the beta and epsilon subunits are located next to each other on the Oenothera ptDNA molecule and are cotranscribed. Immunoanalysis and peptide mapping of in vivo products suggests that a fusion of the two genes may have occurred in the plastome mutant. In contrast to the in vivo data, in vitro translation of the RNA using a heterologous system results in polypeptides which cannot be distinguished from those of wild-type. In addition, neither the mRNA sizes nor plastid DNA restriction fragment patterns differ from wild-type. To reconcile the paradox of these results, it is suggested that either a defect in a translational signal or some other post-transcriptional event is responsible for the mutant phenotype.