Figure 2. Large ribozymes have defined core architectures that are similar across different organisms.

A) Secondary structure schematic diagram emphasizing the shared functional core between the known ancestral (A-type) and bacillus (B-type) P RNA structures of RNase P [11,32]. The dashed box encompasses elements involved in core formation, whereas grey denotes regions that are variable between the structures. Regions that form junctions and that contain universal (cyan) or bacterially (purple) conserved nucleotides are also shown. All conserved nucleotides are labeled. Crystal structures of the T. maritima and Bacillus stearothermophilus P RNAs are shown for comparison [11,32] (PDB 3OK7 and 2A64). B) Schematic diagram of the shared functional core amongst three group I intron structures from different organisms. Colors and labels are as defined in A) with the green, blue, and purple labels in the variable grey helical region corresponding to the different intron structures from Tetrahymena thermophila, Azoarcus sp. BH72, and phage Twort, respectively [12,49,50] (PDB 1X8W, 1U6B, 1Y0Q) [12,49,50]. Despite the presence of different peripheral domains, all three group I structures exhibit the same core domain architecture. Grey dashed regions represent engineered RNA motifs added to promote crystal formation. The diagram in B) was adapted from [30].