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The amazing thing is that, the more we learned about the details of the RNase P RNA structure from both Archaea and Bacteria, the more alike these RNAs seemed. Here are a pair of RNase P RNAs, that of the archaeon Methanothermobacter thermoautotrophicus and the bacterium Ralstonia eutrophus. These RNAs are remarkably alike in structure, the primary differences being the absence of 'P18' in Archaea, and the presence of a conserved internal loop and distal stem in the 'P12' of the archaeal RNA. P19 is absent in a large fraction of bacterial RNase P RNAs, and is apparently a trivial addition where present. The sequences of these RNAs are quite different, but the archaeal RNase P RNAs have the same conserved sequences found in Bacteria, and sequence variation in the two groups is similar.

Given this similarity in the RNA structures and conserved sequences in the archaeal vs bacterial RNase P, we felt it necessary to revisit the apparent complete dependence of the archaeal RNA on protein for catalytic function.