Derivation of the three-dimensional architecture of bacterial ribonuclease P RNAs from comparative sequence analysis.

The secondary structure of bacterial RNase P RNA, a ribozyme responsible for the maturation of the 5' end of tRNAs, is well established on the basis of sequence comparison analysis. RNase P RNA secondary structures fall into two types, A and B, which share a common core formed by the assembly of two main folding domains, but differ in their peripheral elements.A revised alignment of 137 available sequences reveals new covariations allowing for the refinement of both types of secondary structures. Phylogenetic evidence is thus provided for the extension of stems P11, P14, P19, P10.1 and P15.1 through further canonical base-pairs or GAellipsisGA mismatches. These refinements led in turn to a new organization of the catalytic core, with coaxial stackings of helices P2 and P19 as well as P1 and P4. New inter-domain tertiary interactions involve loop L9 and helix P1 and loop L8 with helix P4. These features were incorporated into atomic-scale 3D models of RNase P RNA for representatives of each structural type, namely Escherichia coli and Bacillus subtilis. In each model, the juxtaposition of the core helices creates a cradle onto which the pre-tRNA substrate binds with most evolutionarily conserved residues converging towards the cleavage site. The inner cores of both types are stabilized similarly, albeit by different peripheral elements, emphasizing the modular and hierarchical organisation of the architecture of RNase P RNAs. Similarities are thus apparent between the type A modules, P16/P17/P6 and P13/P14, and their type B analogs, P5.1/P15.1 and P10. 1/P10.1a, respectively. Other noteworthy features of these models include compactness and good agreement with published crosslinking data.