Structural and mechanistic basis of RNA processing by protein-only ribonuclease P enzymes

Ribonuclease P (RNase P) enzymes are responsible for the 5 ' processing of tRNA precursors. In addition to the well-characterised ribozyme-based RNase P enzymes, an evolutionarily distinct group of protein-only RNase Ps exists. These proteinaceous RNase Ps (PRORPs) can be found in all three domains of life and can be divided into two structurally different types: eukaryotic and pro-karyotic. Recent structural studies on members of both families reveal a surpris-ing diversity of molecular architectures, but also highlight conceptual and mechanistic similarities. Here, we provide a comparison between the different types of PRORP enzymes and review how the combination of structural, bio-chemical, and biophysical studies has led to a molecular picture of protein -mediated tRNA processing.