Ribonuclease P (Rnp) is a ubiquitous ribozyme that catalyzes a Mg2 -dependent hydrolysis to remove the 5'-leader sequence of precursor tRNA (pre-tRNA) in all three domains of life []. In bacteria, the catalytic RNA (typically ~120kDa) is aided by a small protein cofactor (~14kDa) []. Archaeal and eukaryote RNase P consist of a single RNA and archaeal RNase P has four or five proteins, while eukaryotic RNase P consists of 9 or 10 proteins. Eukaryotic and archaeal RNase P RNAs cooperatively function with protein subunits in catalysis [].Eukaryotic nuclear RNase P shares most of its protein components with another essential RNP enzyme, nucleolar RNase MRP []. RNase MRP (mitochondrial RNA processing) is an rRNA processing enzyme that cleaves various RNAs, including ribosomal, messenger, and mitochondrial RNAs. It can cleave a specific site within precursor rRNA to generate the mature 5'-end of 5.8S rRNA []. Despite its name, the vast majority of RNase MRP is localized in the nucleolus []. RNase MRP has been shown to cleave primers for mitochondrial DNA replication and CLB2 mRNA. In yeast, RNase MRP possesses one putatively catalytic RNA and at least 9 protein subunits (Pop1, Pop3-Pop8, Rpp1, Snm1 and Rmp1) []. Human RNase MRP complex consists of 267 nucleotides and supports the interaction with and among at least seven protein components: hPop1, hPop5, Rpp20, Rpp25, Rpp30, Rpp38, and Rpp40) and three additional proteins, hPop4, Rpp21 and Rpp14, have been reported to be associated with at least a subset of RNase MRP complexes [].This entry includes animal Rpp38, which is a component of the Rnp and the MRP ribonuclease complexes [].
This family of fungal proteins form a subunit of RNase P, the ribonucleoprotein enzyme that cleaves the leader sequence of precursor tRNAs to generate mature tRNAs. The structure of Pop3 has been assigned the L7Ae/L30e fold []. This RNA-binding fold is also present in human RNase P subunit Rpp38, raising the possibility that Pop3p and Rpp38 are functional homologues.
