RNase P from a photosynthetic organelle contains an RNA homologous to the cyanobacterial counterpart.

RNase P is a ribonucleoprotein enzyme in all organisms and organelles investigated so far, with the exception of chloroplasts where no enzyme-associated RNA has been detected to date. As an approach to answer the question whether an RNA component is present in RNase P from photosynthetic organelles, we have used a phylogenetically oriented strategy and searched for RNase P RNA in a postulated intermediate in plastid evolution, the cyanelle of Cyanophora paradoxa. We have detected a 351 nucleotide long RNA similar to cyanobacterial RNase P RNAs, with a proposed secondary structure that closely resembles a bacterial consensus. The RNA is encoded on the cyanelle genome and copurifies with enzyme activity. The RNA is not catalytically active by itself, but the activity of the cyanelle RNase P holoenzyme is destroyed by nuclease treatment, indicating an essential role of the RNA. Hence cyanelle RNase P, combining properties of bacterial and eukaryotic enzymes, occupies an intermediate position in RNA enzyme evolution. The first description of an RNA component in RNase P from a photosynthetic organelle might thus be an important step towards an understanding of plastid RNase P structure and function.