Figure 6.

Model for the involvement of RNase J in the processing of chloroplast mRNA 5′ ends defined by PPR proteins. Maturation of a generic mRNA (ORF) 5′ end is shown here. Precursor transcripts originate from polycistronic (A) and monocistronic (B) transcriptional units, as well as read-through transcripts from upstream genes such as tRNAs (C). Processing is initiated by endonucleolytic cleavages by RNase J or RNase E within unstructured intergenic regions, or in the case of tRNAs by RNase Z. The resultant 5′ ends are subsequently trimmed to their mature forms by the exonuclease activity of RNase J to PPR protein-bound sites.