One of the primary ways people find structure and coherence in the world is to identify fundamental characteristics common within and between apparently different classes - plants, humans, atoms, stars, etc. In the case of diverse biological life we know that RNA and/or DNA are common to them all. Thus, a deeper understanding of the architecture and interactions of RNA and DNA will lead to a greater understanding of the commonalities underlying all biological life. The intermediary between DNA and protein is RNA. RNA is the only known macromolecule that can encode genetic information and also act as a biocatalyst. In macromolecules like ribonucleases (RNAses), a protein and an RNA work together to form an enzyme that performs one of the fundamental tasks of constructing the protein-making machinery of the cell. Specifically, Rnase P plays a key role in the activation of tRNA and has a catalytic domain and a specificity (S) domain. The S domain alone can bind pre-tRNA directly with micromolar affinity. tRNA is the direct interface between the amino-acid sequence of a protein and the information in DNA. All tRNA's from all organisms have a similar structure. Indeed, a human tRNA can function in yeast cells. Thus, a greater understanding of the architecture and interactions of the S domain -and hence, tRNA - will lead to a better understanding of the process of transcription of genetic information.

Macromolecular crystallography experiments at SSRL and the APS have enabled researchers at Northwestern University to achieve a 3.15 Å resolution crystal structure of the 154-nucleotide S domain of Bacillus subtilis RNase P. The structure reveals the architecture of the S domain and provides a molecular framework for studying the interactions that must occur between tRNA and the ribozyme during pre-tRNA processing. The structure is consistent with the available biochemical data for bacterial RNase P RNA and extends our understanding of RNase P structure across all taxonomic kingdoms. Furthermore, as an important addition to the still limited number of large RNAs of known structure, it advances our knowledge of the general principles of RNA structure and packing.