RNase P from Organelles

Abstract

RNase P is an almost universal enzyme present in Bacteria, Archaea and Eukaryotic nuclei, as well as in mitochondria and chloroplasts. The organellar enzyme shows a great variability in structure and composition. A gene encoding an RNA, homologous to bacterial catalytic RNase P RNA, is found in mitochondria of a diversity of organisms that include fungi, some green algae and jakobid flagellates, but not in mitochondria of higher plants or metazoans. These RNAs are usually highly divergent from their bacterial counterparts, lack one or several of the conserved structural features of bacterial RNase P RNA and are inactive in vitro. The protein moiety of mitochondrial RNase P is largely unknown. When it is known (as in yeast and human mitochondria), it shows no similarity with protein subunits of bacterial or archaeal/eukaryal origin. The human mitochondrial RNase P seems to be a pure protein enzyme composed by three proteins, two of which probably have another additional unrelated function. Much less is known on chloroplast RNase P. Some algal chloroplasts encode in their genome a bacterial-type RNase P RNA, but they are inactive or weakly active in vitro in the absence of protein. Nothing is known on the nature of the protein moiety of these algal chloroplast RNase P. Furthermore, biochemical data suggest that chloroplast RNase P from higher plants might be a protein only enzyme.