Plant mitochondrial genes can be expressed from mRNAs lacking stop codons

The mRNAs of the nad6 and ccmC genes of Arabidopsis and cauliflower were found to be processed upstream of the inframe stop codons. This result was confirmed by northern hybridization and by RT-PCR. There is no evidence that an alternative stop codon is created post-transcriptionally, either by RNA editing or by polyadenylation. The non-stop mRNAs are found in the high molecular weight polysomal fractions, suggesting that they are translated. Using antibodies directed against CcmC, the corresponding protein was detected in Arabidopsis mitochondrial extracts. These observations raise the question of how the plant mitochondrial translation system deals with non-stop mRNAs.