Two exoribonucleases act sequentially to process mature 3'-ends of atp9 mRNAs in Arabidopsis mitochondria.

In plant mitochondria, transcription proceeds well beyond the region that will become mature 3' extremities of mRNAs, and the mechanisms of 3' maturation are largely unknown. Here, we show the involvement of two exoribonucleases, AtmtPNPase and AtmtRNaseII, in the 3' processing of atp9 mRNAs in Arabidopsis thaliana mitochondria. Down-regulation of AtmtPNPase results in the accumulation of pretranscripts of several times the size of mature atp9 mRNAs, indicating that 3' processing of these transcripts is performed mainly exonucleolytically by AtmtPNPase.