RNA binding-proteins interact specifically with the Arabidopsis chloroplast psbA mRNA 5 ' untranslated region in a redox-dependent manner

The 5 ' untranslated region (5 ' UTR) of the psbA mRNA (pshA encodes the PS II reaction center protein, DI) is a key site for FNA-protein interactions in the post-transcriptional regulation of gene expression. In this study, w e mapped the major pshA mRNA 5 ' -terminus at -77 nt, and two minor termini clusters centered at -48 and -64 nt, upstream from the psbA translational start codon of Arabidopsis thaliana. RNA mobility shift, RNase protection a nd UV-crosslinking assays were used to characterize the interaction of chlo roplast proteins with the RNA 5 ' UTR. RNA-protein interactions depended up on a thermolabile secondary structure and specific sequences in a 35 nt reg ion of the 5 ' UTR, which were 80% conserved with the psbA 5 ' UTRs from fi ve other plants. Major and minor proteins of 43- and 30-kDa, respectively, were detected by UV-crosslinking to RNA. Oxidizing conditions abolished the association of the proteins with the 5 ' UTR, while RNA-binding activity w as recovered upon incubation with a reductant. Based on these findings, we hypothesize that post-transcriptional regulation of psbA gene expression in chloroplasts of vascular plants involves redox-dependent interactions betw een specific sequences in the 5 ' UTR and 43- and 30-kDa RNA-binding protei ns.