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PhoPop5 and PhoRpp30 in the hyperthermophilic archaeon Pyrococcus horikoshii, homologues of human ribonuclease P (RNase P) proteins hPop5 and Rpp30, respectively, fold into a heterotetramer [PhoRpp 30(PhoPop5) 2 PhoRpp30], which plays a crucial role in the activation of RNase P RNA (PhopRNA). Here, we examined the functional implication of PhoPop5 and PhoRpp30 in the tetramer. Surface plasmon resonance (SPR) analysis revealed that the tetramer strongly interacts with an oligonucleotide including the nucleotide sequence of a stem-loop SL3 in PhopRNA. In contrast, PhoPop5 had markedly reduced affinity to SL3, whereas PhoRpp30 had little affinity to SL3. SPR studies of PhoPop5 mutants further revealed that the C-terminal helix (a4) in PhoPop5 functions as a molecular recognition element for SL3. Moreover, gel filtration indicated that PhoRpp30 exists as a monomer, whereas PhoPop5 is an oligomer in solution, suggesting that PhoRpp30 assists PhoPop5 in attaining a functionally active conformation by shielding hydrophobic surfaces of PhoPop5. These results, together with available data, allow us to generate a structural and mechanistic model for the PhopRNA activation by PhoPop5 and PhoRpp30, in which the two Cterminal helices (a4) of PhoPop5 in the tetramer whose formation is assisted by PhoRpp30 act as binding elements and bridge SL3 and SL16 in PhopRNA.Keywords: archaea/proteinRNA interaction/ Pyrococcus horikoshii/ribonuclease P/surface plasmon resonance.Abbreviations: 3-D, three-dimensional; PhopRNA, ribonuclease P RNA from P. horikoshii; pre-tRNA, precursor tRNA; RNase P, ribonuclease P; RNP, ribonucleoprotein; RRM, RNA recognition motif; SL3, stem-loop containing P3 helix; SL16, stem-loop containing P16 helix; SPR, surface plasmon resonance.Ribonuclease P (RNase P) is a ubiquitous trans-acting ribozyme that catalyses the processing of 5 0 leader sequences from tRNA precursors (pre-tRNA) and other noncoding RNAs in all living cells (1, 2). In contrast to eubacterial RNase P RNAs, the RNA components in archaea and eukaryotes alone have little catalytic activity in vitro and function in cooperation with protein subunits in substrate recognition and catalysis (3). Hence, archaeal and eukaryotic RNase Ps may serve as a model ribonucleoprotein (RNP) for studying how a functional RNA can be activated by protein cofactors and how the RNP enzymes catalyse biological processes.We earlier found that RNase P RNA (PhopRNA) and five proteins in the hyperthermophilic archaeon Pyrococcus horikoshii OT3 reconstituted RNase P activity that exhibits enzymatic properties like those of the authentic enzyme (4, 5). The P. horikoshii RNase P proteins were designated PhoPop5, PhoRpp21, PhoRpp29, PhoRpp30 and PhoRpp38, according to their sequence homology with the human RNase P proteins hPop5, Rpp21, Rpp29, Rpp30 and Rpp38, respectively (6). Biochemical and structural studies revealed that PhoPop5 and PhoRpp21 form a complex with PhoRpp30 and PhoRpp29, and the resulting complexes, PhoPop5PhoRpp30 and Pho Rpp21PhoRpp29, are involved i...

We analyzed modes of action of ribonuclease P (RNase P) proteins, C5 in Escherichia coli and Rpr2 in Saccharomyces cerevisiae, using a pair of complementary fluorescence-labeled oligoribonucleotides. Fluorescence resonance energy transfer-based assays revealed that RNA annealing and strand displacement activities found in archaeal RNase P proteins are prevalent in eubacterial (C5) and eukaryotic (Rpr2) RNase P proteins.