Structural elements in the archaeal homolog of Pop5 (A) and in the protein component of bacterial RNase P (B) have distinct connectivities, but adopt similar overall mutual orientations (C). (A) Crystal structure of an archaeal homolog of Pop5 (PDB ID 2CZV) shown in red; N and C termini are indicated. (B) Crystal structure of T. maritima RNase P protein (PDB ID 3OKB) shown in blue; N and C termini are indicated. Secondary structure elements (H: α-helices, E: β-strands) are marked according to the designation in Figure 8 and Supplemental Figure S1. (C) Archaeal homolog of Pop5 (PDB ID 2CZV, shown in red) superposed on the protein component of bacterial RNase P (PDB ID 3OKB, shown in blue). (D) An archaeal aPop5/aRpp1 heterodimer (PDB ID 2CZV; aPop5 is in red, aRpp1 is in gold) is shown superposed on the crystal structure of T. maritima RNase P (PDB ID 3OKB; the protein component is in blue, the RNA component is in green).