| Popis: |
Ribonuclease P (RNase P) is an essential endonuclease that catalyzes the cleavage of the 5′ leader sequence from precursor tRNAs (pre-tRNAs). Most forms of RNase P are ribonucleoproteins and the bacterial enzyme possesses a single catalytic RNA and one small protein. In eukaryotes, the enzyme retains a structurally related, catalytic RNA subunit but has a vastly increased protein composition with at least nine protein subunits in yeast and at least ten in humans. The reasons for this additional protein complexity over the bacterial and archaeal RNase P enzymes are not currently understood and potential roles including the acquisition of additional substrates are discussed. Furthermore, in the eukaryote RNase P has evolved into a distinct but closely related enzyme, RNase MRP. This paralogous enzyme has a structurally related RNA subunit and ten protein subunits in yeast, eight of which are also found in the RNase P enzyme. RNase MRP has distinct substrate specificities, primarily involved in ribosomal RNA biogenesis, but also cleaving mitochondrial RNA and mRNAs involved in cell cycle control. We review current information regarding the nuclear RNase P and RNase MRP enzymes in the eukaryotes, focusing on the relationship between these enzymes by examining their composition, structure and substrates. |
