The proposed program is a study of the structure and function of the RNA component of ribonuclease P in Archaea (a.k.a. archaebacteria). The unique characteristic of archaeal RNase P enzymes are that their RNA subunits are not by themselves capable of catalysis in vitro despite their resemblance in sequence to their catalytically-proficient bacterial homologs. The thrust of the proposed program is to develop an understanding of the structural differences between archaeal and bacterial RNase P enzymes and how these similarities and differences contribute to the function (or lack thereof) of the ribozyme. The specific elements of this program are: l. The analysis of archaeal RNase P RNA structure (What is the secondary and tertiary structure of archaeal RNase P RNA and how does it compare to it's catalytically-proficient bacterial homolog?). 2. The analysis of the structural basis of the archaeal RNase P RNA's defect (What difference(s) between the bacterial and archaeal RNase P RNAs are responsible for the biochemical defect?). 3. The analysis of the biochemical nature of the archaeal RNase P RNA's defect (What step(s) of the catalytic cycle can and cannot be performed by archaeal RNase P RNA?). 4. The identification and characterization of additional components of the archaeal RNase P holoenzyme (What are the other components of the catalytically-proficient holoenzyme and how do they contribute to structure and/or catalysis?). 5. A preliminary search for novel catalytic RNAs in the ribosomal RNA processing pathway. The proposed program is health-related because it will provide insight into basic aspects of catalysis by RNA, the relationships between structure and function in RNA, and the nature of interactions of RNA with other macromolecules. This knowledge is essential for the understanding of pathologies mediated by RNAs, such as RNA virus infection and oncogene expression. RNA-based agents, especially catalytic RNAs such as RNase P, will clearly be an important facet of gene-therapy treatments for a variety of diseases. Archaeal RNase P's, because of the dependence of their RNAs on other additional factors for function, provide an important system for the examination of essential elements of RNase P RNA structure and function.