Crystal structures of type T archaeal ribonuclease P Rpp30, Rpp30/Pop5, and L7Ae provide insights into a reduced RNase P.

RNase P is primarily responsible for processing the 5' end of precursor transfer RNA (tRNA). Although there are protein-only RNase P enzymes, the most widely distributed RNase Ps form ribonucleoprotein complexes where the number of protein components varies across evolutionary domains. Ribonucleoprotein RNase P enzymes universally contain a single RNA component. Pyrobaculum, a genus of archaeal hyperthermophiles, possess a minimal RNase P composed of a small RNA subunit and four small proteins. To understand the structure of this minimal RNase P, high-resolution structures of three protein components from Pyrobaculum were determined. These structures reveal that the proteins closely resemble their larger homologs, although entire secondary structure elements are absent in some instances. Modeling of the RNA subunit suggests a structure closely related to the RNA components of other RNase P complexes, but with a minimal S-domain containing only a single T-loop. The modeling further supports the formation of an RNase P complex that retains all the elements needed for tRNA recognition and processing. Finally, RNA composition analysis by size exclusion chromatography indicates that the L7Ae protein component may assist in the folding and structural stabilization of the RNA subunit.