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

Summary

In a plastid genome (plastome) mutation of Oenothera hookeri, at least two of the plastome-coded polypeptides (the β and ε subunits) of the chloroplast ATP synthase are directly affected. As in other plastid chromosomes, the genes for the β and ε 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.