The protein‐only RNase Ps, endonucleases that cleave pre‐tRNA: Biological relevance, molecular architectures, substrate recognition and specificity, and protein interactomes

Protein‐only RNase P (PRORP) is an essential enzyme responsible for the 5′ maturation of precursor tRNAs (pre‐tRNAs). PRORPs are classified into three categories with unique molecular architectures, although all three classes of PRORPs share a mechanism and have similar active sites. Single subunit PRORPs, like those found in plants, have multiple isoforms with different localizations, substrate specificities, and temperature sensitivities. Most recently, Arabidopsis thaliana PRORP2 was shown to interact with TRM1A and B, highlighting a new potential role between these enzymes. Work with At PRORPs led to the development of a ribonuclease that is being used to protect against plant viruses. The mitochondrial RNase P complex, found in metazoans, consists of PRORP, TRMT10C, and SDR5C1, and has also been shown to have substrate specificity, although the cause is unknown. Mutations in mitochondrial tRNA and mitochondrial RNase P have been linked to human disease, highlighting the need to continue understanding this complex. The last class of PRORPs, homologs of Aquifex RNase P (HARPs), is found in thermophilic archaea and bacteria. This most recently discovered type of PRORP forms a large homo‐oligomer complex. Although numerous structures of HARPs have been published, it is still unclear how HARPs bind pre‐tRNAs and in what ratio. There is also little investigation into the substrate specificity and ideal conditions for HARPs. Moving forward, further work is required to fully characterize each of the three classes of PRORP, the pre‐tRNA binding recognition mechanism, the rules of substrate specificity, and how these three distinct classes of PRORP evolved. This article is categorized under: RNA Structure and Dynamics > RNA Structure, Dynamics and Chemistry RNA Structure and Dynamics > Influence of RNA Structure in Biological Systems Three distinct classes of PRORP evolved to cleave the 5′ leader sequence from pre‐tRNA. Beyond available structure, kinetic, and thermodynamic data, there is more to learn about the protein‐interaction network, substrate specificity, and disease‐linked mutations related to PRORP.