both eukaryotes and prokaryotes and it cleaves a pre-tRNA to generate the mature 5’ end of the tRNA. RNase MRP is found only in eukaryotes, and is involved in rRNA processing, which is the conversion of preribosomal RNA into mature rRNA through splicing, modifications, and cleavage. The exact mechanism is described above. Evolutionary link These two ribonucleases are most likely evolutionarily related through a common ancestor, since they have common protein subunits and can be folded into very similar secondary structures. There are many conserved regions in these two ribonucleases. Sequences of the CR-I, CR-V, and CR-IV genes in domain 1 of the P4 helical region are conserved, with the consensus sequence in CR-IV being AGNNNNA for RNAse P and AGNNA for RNase MRP. CR-II and CR-III are also conserved in domain 2 of P RNA. The P3 helix is also conserved in both ribonucleases in all eukaryotes, but the function of this helix is not yet clear. These conserved regions are evidence of the close phylogenetic relation between these two important ribonucleoprotein complexes. Diseases associated with RNAse MRP gene Metaphyseal dysplasia without hypotrichosis (MDWH), anauxetic dysplasia (AD), kyphomelic dysplasia (KD), Omenn syndrome (OS) are diseases associated with mutated and (or) dysfunctional RNAse MRP activity, hence, the RMRP gene. Cartilage–hair hypoplasia Mutations in the RNA component of RNase MRP cause cartilage–hair hypoplasia(CHH), a pleiotropic human disease. Two categories of mutations involving RNAse MRP have been identified in patients with CHH. The first type is when an insertion, duplication, or triplication occurs at the promoter of the RNAse MRP gene between the TATA box and the transcription initiation site. This causes the initiation of RNAse MRP to be slow, or to not occur at all. The second category consists of mutations that are in the transcribed RNA made by the RNAse MRP. Patients with CHH have been identified to have over 70 different mutations in the RNA transcript made by RNAse MRP, whereas around 30 distinct mutations have been identified in the promoter region of the RNAse MRP gene. Most CHH patients have a combination of either a promoter mutation in one allele along with a RNAse MRP RNA mutation in the other allele, or a combination of two RNAse MRP RNA mutations in both alleles. The fact that there is not often a mutation in the promoter region in both alleles shows the lethality of not having this RNA present