RMRP is the RNA component of the RNase MRP protein complex. It functions as a RNA and is not translated into a protein.

The RMRP gene is transcribed by the DNA dependent RNA polymerase III. The gene contains typical sequence elements of a RNA Pol III type 3 promoter. The core sequence elements such as the PSE element and a TATA box can be found upstream of the transcription initiation site of the RMRP gene. In addition, transcription factor binding sites like a SP1 binding element and an octamer (recruits the transcription factor Oct-1) sequence could serve as distal sequence elements (DSE) to enhance the transcription of RMRP similar to the DSE element of the human U6 snRNA gene.
Expression RMRP is strongly and ubiquitously expressed in mouse embryos (as an example an E15.5 mouse embryo is shown). In bone Rmrp is more strongly expressed in hypertrophic chondrocytes and pericondrium than in the zone of proliferating chondrocytes. There is also very strong expression in the epiphysis. In humans RMRP shows also a very strong expression in adult tissues. A little weaker expression is observed in skeletal muscle when compared to the GAPDH hybridization control. In Xenopus laevis oocytes RMRP is stronger expressed in developmental stages with a higher content of mitochondria.
Function RMRP has been mostly studied in yeast and multiple functions have been attributed to this ribonucleoprotein complex, called RNase MRP. The yeast orthologues gene is called nme1. Firstly, it plays a role in mitochondrial DNA replication. It cleaves the RNA primer of RNA/DNA hybrid. This hybrid formation initiates the mitochondrial DNA replication. It is also involved in the RNA primer formation. Secondly, RMRP is involved in the progression of the cell cycle at the end of mitosis. Some nme1 mutants arrest in the late cycle of mitosis. These mutants present morphologically as large budded cells with dumbbell-shaped nuclei, and also exhibit extended spindles. This cell cycle arrest might be due to an increased level of CLB2. In wild type yeast strains the 5UTR of CLB2 is cleaved by the RNase MRP complex. This causes a rapid degradation of the CLB2 mRNA, which leads to a cell cycle progression. Thirdly, RMRP also plays a role in the ribosomal RNA processing. In yeast, it cleaves pre-ribosomal RNA at the A3 site thus helps the maturation of the short and active form of the 5.8S rRNA.
Homology RNase P is also a ribonucleoprotein endoribonuclease that is mainly involved in tRNA precursor maturation. RNase P and RNase MRP have eight proteins in common. The protein RPR2p is unique to the RNase P complex. In yeast two RNase MRP specific proteins have been identified; snm1 and rmp1. The loss of function of snm1 leads to a defect in the chromosome segregation during mitosis. But the exact mechanism is not understood yet.

So far 93 different mutations have been identified in CHH patients. These include 24 promoter mutations that are either duplications, triplications or insertions that occur exclusively between the TATA box and the transcription start site. The size of the promoter mutations varies between 6 and 24 bp. In vitro studies have shown that these promoter mutations decrease the level of the RMRP transcript but do not abolish the RNA transcription completely. 69 different mutations in the 267 bp long transcript have been found up to now. 57 of these are single base pair substitutions spread out over the entire transcript. Also 11 small insertions, duplications and deletions have been found. The largest deletion identified so far involves the last 10 bp of the RMRP transcript.
The mutations lead to a significant decrease of the RMRP RNA level in CHH, despite the nature of the mutation. These mutations might influence the secondary structure of the RNA, the binding of the proteins to the RNA or the RNA stability itself.
The most frequently found mutation among CHH patients is a 70 A>G transition mutation with an ancient founder origin established in Finland and is the only mutation found in Amish CHH patients. Patients either carry two mutations in the RMRP transcript or are compound heterozygous for a promoter mutation and a transcript mutation. Interestingly, none of the patients exhibit two promoter mutations.
In addition 11 polymorphisms and 17 rare sequence variants have been observed. This is very remarkable considering the small size of the RMRP gene.
So far no complete deletion of the entire RMRP gene has been observed. This suggests that complete loss of RMRP function might be incompatible with life. This is also supported by the fact that the knock out of the yeast NME1 gene is lethal.