We have used an in vitro system to characterize ribonuclease activities present in spinach chloroplasts. We show that 3' end maturation of petD mRNA, which encodes subunit IV of the cytochrome b6/f complex, is affected by a 33-kDa protein that binds to a hairpin structure at the 3' end of the mature mRNA. Binding of the 33-kDa protein to the petD hairpin structure decreases the efficiency of 3'...
