Characterization of RNA-based and protein-only RNases P from bacteria encoding both enzyme types.

A small group of bacteria encode two types of RNase P, the classical ribonucleoprotein (RNP) RNase P as well as the protein-only RNase P HARP (omolog of Nase ). We characterized the dual RNase P activities of five bacteria that belong to three different phyla. All five bacterial species encode functional RNA (gene ) and protein (gene ) subunits of RNP RNase P, but only the HARP of the thermophile (phylum Thermodesulfobacteria) was found to have robust tRNA 5'-end maturation activity in vitro and in vivo in an RNase P depletion strain. These findings suggest that both types of RNase P are able to contribute to the essential tRNA 5'-end maturation activity in , thus resembling the predicted evolutionary transition state in the progenitor of the Aquificaceae before the loss of and genes in this family of bacteria. Remarkably, RNase P RNA is transcribed with a P12 expansion segment that is posttranscriptionally excised in vivo, such that the major fraction of the RNA is fragmented and thereby truncated by ∼70 nt in the native host as well as in the complementation strain. Replacing the native P12 element of RNase P RNA with the short P12 helix of RNase P RNA abolished fragmentation, but simultaneously impaired complementation efficiency in cells, suggesting that intracellular fragmentation and truncation of RNase P RNA may be beneficial to RNA folding and/or enzymatic activity.