Phosphorylation is required for high-affinity binding of DBP, a yeast mitochondrial site-specific RNA binding protein

All yeast mitochondrial mRNAs terminate at their 3' ends with a conserved dodecamer sequence, a site for high-affinity binding by DBP (dodecamer binding protein). Using purified DBP, we show that binding requires an intact dodecamer site and is enhanced by the presence in an oligonucleotide of the immediate 4-5 upstream nucleotides. Binding affinity varied from 0.25 to 0.85 nM towards a set of RNA oligonucleotides containing messenger specific upstream sequences in addition to the dodecamer site. Furthermore, we show that phosphatase treatment of DBP abolishes its specific binding, indicating the involvement of reversible phosphorylation in the regulation of its binding activities. This finding will further our understanding of the mechanism of DBP in the regulation of RNA metabolism in yeast mitochondria.