RNASE-P FROM A PHOTOSYNTHETIC ORGANELLE CONTAINS AN RNA HOMOLOGOUS TOTHE CYANOBACTERIAL COUNTERPART

RNase P is a ribonucleoprotein enzyme in all organisms and organelles investigated so far, with the exception of chloroplasts where no enzym e-associated RNA has been detected to date. As an approach to answer t he question whether an RNA component is present in RNase P from photos ynthetic 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 pr oposed secondary structure that closely resembles a bacterial consensu s. The RNA is encoded on the cyanelle genome and copurifies with enzym e activity The RNA is not catalytically active by itself, but the acti vity of the cyanelle RNase P holoenzyme is destroyed by nuclease treat ment, 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 o f an RNA component in RNase P from a photosynthetic organelle might th us be an important step towards an understanding of plastid RNase P st ructure and function. (C) 1996 Academic Press Limited