Chloroplast mRNA 3′-end processing by a high molecular weight protein complex is regulated by nuclear encoded RNA binding proteins

Abstract

In the absence of efficient transcription termination correct 3′-end processing is an essential step in the synthesis of stable chloroplast mRNAs in higher plants. We show here that 3′-end processing in vitro involves endonucleolytic cleavage downstream from the mature terminus, followed by exonucleolytic processing to a stem-loop within the 3′-untranslated region. These processing steps require a high molecular weight complex that contains both endoribonucleases and an exoribonuclease. In the presence of ancillary RNA binding proteins the complex correctly processes the 3′-end of precursor RNA. In the absence of these ancillary proteins 3′-end maturation is prevented and plastid mRNAs are degraded. Based on these results we propose a novel mechanism for the regulation of mRNA 3′-end processing and stability in chloroplasts.