RNA-BINDING PROTEINS OF 37 38-KDA BIND SPECIFICALLY TO THE BARLEY CHLOROPLAST PSBA 3'-END UNTRANSLATED RNA/

The stability of the psbA mRNA increases during barley chloroplast dev elopment eventually reaching a half-life of over 40 h. Translation of psbA mRNA is also regulated in a complex way. Sequence-specific RNA bi nding proteins may modulate the translation or stability of the psbA m RNA during chloroplast development. UV cross-linking assays revealed t hat chloroplast proteins of 37 and 38 kDa bind specifically to the 3' end of psbA transcripts and not to the 5' end of psbA or rbcL transcri pts. The two RNA-binding proteins were partially purified by ammonium sulfate precipitation followed by heparin agarose chromatography. Dele tion and site-directed mutation analysis demonstrated that the 37/38RN Ps bind in a 30 nucleotide region immediately downstream from the tran slation termination codon and upstream of sequences capable of forming a stem-loop structure in the 3' end of psbA transcripts. Single-base changes that diminish the binding of the 37RNP also reduce binding of the 38RNP suggesting that these proteins may bind as a heterodimer. Th e 37/38RNPs that bind within the 3' end of psbA transcripts could modu late transcription termination, translation or mRNA stability.